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307 LIBRARY “—
Michigan State

‘nu vlf‘il'Ch
VUqu

This is to certify that the
thesis entitled

THE INFLUENCE OF WATER CONTENT IN
HYDRATED SUPERABSORBENT POLYMER ON
DIELECTRIC PROPERTIES, ANTENNA RADIATED
POWER, AND RF ID TAG READABILITY

presented by
Xuebing Zhang

has been accepted towards fulﬁllment
of the requirements for the

degree' In Packaging

”ﬂow/“M

Major Proanature
73/91 f/ 0 é

Date

 

 

MSU is an Afﬁrmative Action/Equal Opportunity Institution

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PLACE IN RETURN BOX to remove this checkout from your record.
TO AVOID FINES return on or before date due.
MAY BE RECALLED with earlier due date if requested.

 

DATE DUE DATE DUE DATE DUE

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

5/08 K‘IProlecc&Pres/CIRCiDateDue indd

 

THE INFLUENCE OF WATER CONTENT IN HYDRATED
SUPERABSORBENT POLYMER ON DIELECTRIC PROPERTIES, ANTENNA
RADIATED POWER, AND RFID TAG READABILITY
By

Xuebing Zhang

A THESIS
Submitted to
Michigan State University
in partial fulﬁllment of the requirements
for the degree of
MASTER OF SCIENCE
School of Packaging

2006

ABSTRACT

THE INFLUENCE OF WATER CONTENT IN HYDRATED
SUPERABSORBENT POLYMER ON DIELECTRIC PROPERTIES, ANTENNA
RADIATED POWER AND RFID TAG READABILITY

By Xuebing Zhang
The performance and stability of RF ID systems in a supply chain relies on the readability of
passive RFID transponders. This thesis presents research on correlation and inﬂuence of
readability on passive RFID transponders and water content in products simulated by hydrated

superabsorbent polymer (SAP).

High water absorbable SAP provided a wide range of simulation options, from 45% to 95%
water. The dielectric property in terms of permittivity of the hydrated SAP samples was
characterized and differentiated by S-parameter measurement using a HP8510C network analyzer
with a WR340 waveguide. Moreover, radiated power measurement and a readability survey using
Alien® 915 MHz squiggle RFID tags with the same SAP specimens were performed with an

R&S® NRP-ZZZ power sensor with LabVIEW® program and Alien® RF ID Gateway software.

The research results showed that the weight percent of water content in saturated SAP affected
permittivity. The dielectric constant, Re( 8 r ) and water content have a nearly linear relationship.
The loss factor, Im( 8r ) showed complicated fluctuations and sudden declines in some frequency
ranges. High water concentration in the SAP mixtures indicated high power loss and low
readability. More than 75% water content in the samples usually attained near 0% readability.
Reader antenna style, position and transponder orientation showed diﬁemnt inﬂuence on
readability and power loss with the same saturated samples. This research shows that product
content and packaging operations are challenges to successful implementation of RFID system in

supply chain.

 

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ACKNOWLEDGEMENTS

I am indebted to Dr Robert Clarke, my major advisor and committee chair, for all his
guidance and support during the thesis preparation and all throughout my masters
program in the School of Packaging, MSU. Dr Clarke has generously given his time to
discuss with me and to provide his knowledge and patience, which have been invaluable

to this research and my life.

I would like to thank Dr. Leo Kempel and Dr. Ed Rothwell for their contribution at
material characterization in this research as well. Without their participation and guidance,

all measurements of material characterization are impossible.

I would like to thank Mr. Andrew Eric Bogle and Mr. Steve Cossmann, who contributed

their time, experience, work and patient and cooperation in this research.

Thanks to Dr. Bruce Harte as a committer member providing advices and guiding for this

research and preparation of the thesis.

Thanks to Mr. Bill Lindsay at Grain Processing Corporation who provided

superabsorbent polymer for this research.

Especially, I want to thank my son Yifan Andrew Zhang, My parents Zhongde, Huinong,
My brother Xuefei, their love and support is always the source of power which I am get
exhausted. In addition, I would like to thank to Dr. Weijuan Ni, who provided many help

in my master program.

iii

 

 

L

TABLE OF CONTENTS

 

 

 

 

 

 

 

 

 

 

 

 

 

 

LIST OF TABLES VIII
LIST OF FIGURES IX
KEY TO ABBREVIATIONS XV
LIST OF PRINCIPAL LETTER SYMBOLS XVIII
CHAPTER 1 INTRODUCTION 1
1.] OVERVIEW ............................................................................. -1
1.2 RFID PUZZLES ............................................................ . - 2
1.3 RESEARCH ASPECTS .............................................................................................................................. 3

I .4 RESEARCH GOALS ................................................................. - . 4
1.5 THESIS SUMMARY ............................................................................. . _ ..5
CHAPTER 2 LITERATURE REVIEW 6
2.] AUTOMATIC IDENTIFICATION TECHNOLOGIES .................................................... 6
2.2 BRIEFLY HISTORY OF RFID ................................................................................................................... 6
2.3 RF ID SYSTEM COMPONENTS ........................................................................... 7
2.3.1 Transponder .................................................................................................................................. 7

2. 3.2 lnterrogator ................................................................................................................................... 9

2. 3. 3 Computer and Backbone Software .............................................................................................. 10

2.4 BASIC PRINCIPLES ................................................................................................................................ IO

2. 4. 1 Frequency Allocation .................................................................................................................. 10
2.4.2 Near Field and F or Field ............................................................................................................ 11

2. 4.3 Read Range and Power Assumption ............................................................................................ 13

2. 4.4 Modulation ................................................................................................................................... l 4

2.5 ELECTROMAGNETIC PROPERTIES ................................. - . ........................................ I 5

2. 5. I Dipole Moment and Molecular Polarity ...................................................................................... 15

2. 5.2 Dielectric Permittivity ................................................................................................................. l 6
2.5.3 Loss Tangent ................................................................................................................................ l8

2. 5. 4 Dielectric Absorption ................................................................................................................... l 8

2.6 WATER CONTENT IN FOODS ................................................................................................................. I9

2. 6. 1 Water Activity .................................. . ........................................................................................... l 9

2. 6.2 Water Forms ................................................................................................................................ 20

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

2. 6.3 Dielectric Properties ................................................................................................................... 21

2. 6. 4 Gel Structure and Food Biopolymers .......................................................................................... 22
2.7 SUPERABSORBENT POLYMER ............................................................................................................... 23
2. 7.1 History of Superabsorbent ........................................................................................................... 23

2. 7.2 Structure and Properties .............................................................................................................. 24

2. 7.3 Mechanism of Water Absorption ................................................................................................. 25
2.8 PREVIOUS RESEARCH ............................................................................ ....25
2. 8. 1 RFID Application ........................................................................................................................ 25

2. 8.2 Material Characterization ........................................................................................................... 2 7

2. 8. 3 Material ....................................................................................................................................... 2 7
2.9 RELEVANCY ............................................................................................................. 27
CHAPTER 3 METHODLOGY 29
3.1 INTRODUCTION ..................................................................................................... 29
3.2 PRODUCT SIMULATION ............................................... 31
3.3 MEASUREMENT DESCRIPTION ................................. ...32
3.4 SUPERABSORBENT SPECIFICATIONS ................................. 33
3.5 SPECIMEN PREPARATION ......................................................................... 33
3.6 DETERMINATION OF WATER CONTENT ................................................................................................ 34
3.7 S-PARAMETER MEASUREMENT ..................................................................... .35
3.8 POWER MEASUREMENT ....................................................................................................................... 36
3.9 READABILITY SURVEY .............. 36
CHAPTER 4 MATERIAL CHARACTERIZATION 18
4.] MATERIAL CHARACTERIZATION ....................................................................... ‘38
4.2 MEASUREMENT EQUIPMENT ....................................................... .39
4. 2. 1 Vector Network Analyzer ............................................................................................................. 39
4.2.2 Waveguide ................................................................................................................................... 39
4.3 EXPERIMENTAL SETUP ....................................................................................... 40
4.4 CALIBRATION PROCESSING ............................................................................ 41
4.5 MEASUREMENT CALIBRATION ....................................................................... 42
4.6 CALIBRATION OF NETWORK ANALYZER ............................................................... 43
4. 6.] One-path 2-Port Calibration ....................................................................................................... 43
4.6.2 Full 2-port and TRL Calibrations ................................................................................................ 44
4.6.3 Full 2-Port Calibration ................................................................................................................ 44
4.6.4 TRL Calibration ........................................................................................................................... 44

4. 6.5 TRL Calibration Procedure ......................................................................................................... 45

4.7 S-PARAMETERS MEASUREMENT PROCEDURE ....................................................... 46

 

 

 

 

 

 

 

 

 

 

 

 

 

4.8 VALIDATION OF MEASUREMENTS ........................................................................................................ 47
4.9 EXTRACTION PROCESS ....... . -- - .................................... 48
CHAPTER 5 POWER MEASUREMENT AND READABILITY SURVEY <1
5.1 INTRODUCTION .................................................................................................................................... 5 I
5.2 EXPERIMENTAL EQUIPMENT ........................................ .. 52
5. 2.1 Power Sensor ............................................................................................................................... 52
5.2.2 Calibration .................................................................................................................................. 53
5.2.3 2- Wire Folded Dipole Antenna .................................................................................................... 55
5.2.4 RFID Equipment .......................................................................................................................... 55
5.2.5 Virtual Power Meter C onﬁguration ............................................................................................ 56
5.2.6 Lab VIEW Programming .............................................................................................................. 5 7
5.3 RECEIVING ANTENNA PLACEMENT ..................................................... - ...................... 58
5.4 ALUMINUM SHIELDING ........................................................................................................................ 59
5.5 MEASUREMENT DEVIATION ................................................................................................................. 60
5.6 POWER MEASUREMENT PROCEDURE ................................................................................................... 63
5.7 READABILITY SURVEY ........................................................................... 64
5.8 ANTENNA ORIENTATION. - - -- ............................................... 65
CHAPTER 6 RESULTS AND DISCUSSION 67
6.1 S-PARAMETERS ........................................................................................................ 67
6.2 VALIDATION ................................................................................... -- ............................. 80
6.3 PERMITTIVITY ...................................................................................................................................... 85
6.4 LOSS FACTOR ....................................................................................................................................... 93
6.5 LOSS TANOENT .................................................................................................................................... 95
6.6 POWER MEASUREMENT ....................................................................................................................... 99
6. 6. 1 Antenna Style ............................................................................................................................. l 00
6.6.2 Shielding .................................................................................................................................... l 02

6. 6. 3 Circular Antenna ....................................................................................................................... 103

6. 6. 4 Linear Antenna .......................................................................................................................... 106
6.7 CRITICAL POWER ............................................................................................................................... 108
6.8 READABILITY SURVEY .................................................................................... 109
6. 8. 1 Readability Decaying Model in Open-air .................................................................................. 109
6.8.2 Tag Orientation ......................................................................................................................... 110

6. 8. 3 Water Content ............................................................................................................................ I l 1

vi

CHAPTER 7 CONCLUSIONS

 

7.] MATERIAL CHARACTERIZATION ........................................................................................................

7.2 RECEIVED RADIATED POWER ............................................................................................................

7.3 READABILITY .....................................................................................................................................

7.4 LIMITATIONS OF THIS RESEARCH .......................................................................................................

7.5 FUTURE RESEARCH ...........................
7.6 SUMMARY CONCLUSION ...................

APPENDIX A S-PARAMETERS IN SATURATED SAP (90%)

APPENDIX B EXPERIMENTAL PERMITTIVITY AND PERMEABILITY

APPENDIX C GLOSSARY

oooooooooooooooooooo

 

 

 

 

 

 

REFERENCES

 

Vii

116

116
117
117
118
119
120

122

125

126

128

IKE- _.‘ ‘~'

 

 

 

Tabl

Tab

Tab
and

Tat

Tal

Tal

Ta

Ta

T2

LIST OF TABLES

Table 2.1 EPC tags classes .................................................................................................. 9
Table 2.2 Near ﬁeld and far ﬁeld regions ......................................................................... 12
Table 2.3 Dielectric properties of foodstuffs and other packaging materials at 2.4SGHz

and 68°F ............................................................................................................................ 22
Table 4.1 WR340 waveguide characteristics .................................................................... 40
Table 5.1 Power measurement range ................................................................................ 53
Table 5.2 Descriptive statistics of measurement deviation ............................................... 61
Table 6.] Correlations of water concentration and sample relative permittivity .............. 90
Table 6.2 Average shielding power loss (dB) ................................................................. 102
Table 6.3 Half decaying rate of readability and least power in free space ..................... 108

viii

LIST OF FIGURES

Figure 2.1 UHF 915 MHz RF ID transponder, reader, and antenna .................................... 8
Figure 2.2 RF ID signal propagation and backscattering .................................................... 9
Figure 2.3 Attenuation of magnetic strength vs. distance in near ﬁeld region ................. 11
Figure 2.4 FSK and PSK digital signal modulation .......................................................... 15
Figure 2.5 Orientation of atoms and direction of the electric dipole relative in H20 ....... 16
Figure 2.6 Complex permittivity and loss tangent ........................................................... 18

Figure 2.7 Hydrated superabsorbent polymer sample, with more than ten times of its

weight of water absorbed by the SAP particles .......................................... _. ..................... 23
Figure 2.8 Crosslinking structure in a superabsorbent polymer ....................................... 24
Figure 3.1 Dimension of 2-wire folded dipole antenna ................................................... 30
Figure 3.2 Hydrated SAP mixtures in the sample window ............................................... 32
Figure 4.1 HP-8510C Network Analyzer and panel block .............................................. 39
Figure 4.2 WR340 waveguide components and cross section ......................................... 40
Figure 4.3 VNA and WR340 waveguide set-up ............................................................... 42
Figure 4.4 Waveguide sample holder ............................................................................... 43
Figure 4.5 WR340 standard calibration line section ......................................................... 45
Figure 4.6 SAP specimens in the wrap ............................................................................. 46

Figure 4.7 Transmission and reﬂection of signals: Side view of waveguide with specimen
layer ................................................................................................................................... 47

Figure 4.8 FORTRAN extractor: input the initial values and extract permittivity and

permeability ...................................................................................................................... 48
Figure 5.1 Default data acquisition interface for power sensor ........................................ 52
Figure 5.2 Average power measurement .......................................................................... 54
Figure 5.3 Two-wire folded half-wavelength dipole antenna of power sensor ................ 55
Figure 5.4 Alien Squiggle ALL-9338 RFID tag .............................................................. 56

Figure 5.5 Program interface of virtual power meter for R&S® NRP-Z22 power sensor57

Figure 5.6 LabVIEW diagram of virtual power meter ..................................................... 58
Figure 5.7 Experimental setup of power measurement and readability survey ................ 59
Figure 5.8 Periodical ﬂuctuation of discrete average power reading ............................... 60
Figure 5.9 Stable average power in measurement ............................................................ 61
Figure 5.10 Continuous decline or incline deviation in power measurement ................... 62
Figure 5.11 Undulation in power measurement ................................................................ 62
Figure 5.12 Comparison of measurement accuracy .......................................................... 63

Figure 5.13 Hydrated SAP specimen, dipole antenna connected with power meter and
reader antenna in the other side of sample window .......................................................... 64

Figure 5.14 Power sensor and receiving antenna in one Side, mobile reader antenna in the

other side ........................................................................................................................... 65
Figure 5.15 Alien RFID Gateway for readability survey ................................................. 65
Figure 5.16 Polarization losses in a linear reader antenna ................................................ 66

Figure 6.1 The diagram of incident waves (a1, a2), reﬂected waves (b1, b2) and S-
parameters in a typical two-port network ........................................................................ 68

Figure 6.2Comparison of 811 in SAP specimen with 70% water content ....................... 70

Figure 6.3 Comparison of 822 in SAP specimen with 55% water content ...................... 70
Figure 6.4 Comparison of $21 in SAP Specimen with 80% water content ...................... 71
Figure 6.5 Comparison of 812 in SAP specimen with 60% water content ...................... 72
Figure 6.6 Comparison of experimental 811 (real) in SAP mixtures (12 mm) ................ 72
Figure 6.7 Comparison Of experimental 811 (real) in SAP mixtures (7 mm) .................. 73
Figure 6.8 Comparison Of experimental Sll (img) in SAP mixtures (12 mm) ................ 73
Figure 6.9 Comparison of experimental Sll (img) in SAP mixtures (7 mm) .................. 74
Figure 6.10 Comparison of experimental 822 (real) in SAP mixtures (12 mm) .............. 74
Figure 6.11 Comparison of experimental S22 (real) in SAP mixtures (7 mm) ................ 75
Figure 6.12 Comparison of experimental $22 (img) in SAP mixtures (12 mm) .............. 75
Figure 6.13 Comparison of experimental 822 (img) in SAP mixtures (7 mm) ............... 76
Figure 6.14 Comparison of experimental 812 (real) in SAP mixtures (12 mm) .............. 76
Figure 6.15 Comparison of experimental S 12 (real) in SAP mixtures (7 mm) ................ 77
Figure 6.16 Comparison of experimental 812 (img) in SAP mixtures (12 mm) .............. 77
Figure 6.17 Comparison of experimental S 12 (img) in SAP mixtures (7 mm) ................ 78
Figure 6.18 Comparison of experimental 821 (real) in SAP mixtures (12 mm) .............. 78
Figure 6.19 Comparison of experimental 821 (real) in SAP mixtures (7 mm) ................ 79
Figure 6.20 Comparison of experimental S21 (img) in SAP mixtures (12 mm) .............. 79
Figure 6.21 Comparison of experimental $21 (img) in SAP mixtures (7 mm) ................ 80

xi

Figure 6.22 Comparison of loss factors in SAP samples (55%) ....................................... 81

Figure 6.23 Comparison of loss factors in SAP samples (60%) ....................................... 82
Figure 6.24 Comparison of loss factors in SAP samples (65%) ....................................... 82
Figure 6.25 Comparison of loss factors in SAP samples (70%) ....................................... 82
Figure 6.26 Comparison of loss factors in SAP samples (75%) ....................................... 83
Figure 6.27 Comparison of loss factors in SAP samples (80%) ....................................... 83
Figure 6.28 Comparison of loss factors in SAP samples (85%) ....................................... 84
Figure 6.29 Comparison of loss factors in SAP samples (90%) ....................................... 84
Figure 6.30 Comparison of loss factors in SAP samples (95%) ....................................... 85

Figure 6.31 Comparison of experimental permittivity (EPR) and permeability (MUR).. 86
Figure 6.32 Comparison of permittivity in SAP with different water content (12 mm) .. 88
Figure 6.33 Comparison of permittivity in SAP with different water content (7 mm) 88
Figure 6.34 Comparison of permittivity in SAP with different water content (12 mm) .. 89
Figure 6.35 Comparison of permittivity in SAP with different water content (7 mm) 89
Figure 6.36 Correlation of relative permittivity in different Sample thickness ................. 90

Figure 6.37 Pennittivity vs. water concentration at 2.45GHz in different sample thickness
........................................................................................................................................... 91

Figure 6.38 Standard deviation of relative permittivity in different sample thickness ..... 92
Figure 6.39 Estimated permittivity of 100% water ........................................................... 92

Figure 6.40 Comparison of loss factor in SAP with different water content (12 mm) ..... 94

xii

Figure 6.4] Comparison of loss factor in SAP with different water content (7 mm) ....... 94

Figure 6.42 Loss factor of different samples ................................................................... 95
Figure 6.43 Standard deviation of loss factor in different thickness ................................ 95
Figure 6.44 Loss tangent in 12 mm SAP samples ............................................................ 96
Figure 6.45 Loss tangent in 7 mm SAP samples .............................................................. 97
Figure 6.46 Comparison of loss tangent at 2.45 GHz in 7 mm samples ........................... 97
Figure 6.47 Comparison of average loss tangent in SAP samples ................................... 98
Figure 6.48 Comparison of loss tangent of SAP Mixtures (65%) .................................... 99
Figure 6.49 Antenna received power between reader antenna and tag ........................... 100
Figure 6.50 Power decaying in Open-air with circular antenna ...................................... 101
Figure 6.51 Power decaying in Open-air with linear antenna ........................................ 101
Figure 6.52 Tag orientation loss in different antennas ................................................... 102
Figure 6.53 Power with Shielding .................................................................................. 103
Figure 6.54 Power attenuation of circular antenna (H) ................................................... 104
Figure 6.55 Power attenuation of circular antenna (V) ................................................... 104
Figure 6.56 Power loss in 50% and 75% SAP ................................................................ 105
Figure 6.57 Inﬂuence of water content on power loss .................................................... 105
Figure 6.58 Average power loss in 70% SAP specimen .............................................. 106
Figure 6.59 Comparison of power attenuation with saturated SAP samples .................. 106
Figure 6.60 Comparison of power attenuation with saturated SAP samples .................. 107

xiii

 

FIE
F12
F12

Fig

Figure 6.61 Comparison of power attenuation with 50% and 75% water content ......... 107

Figure 6.62 Comparison of received power with circular and linear antenna ................ 108
Figure 6.63 Readability decaying in free space .............................................................. 110
Figure 6.64 Comparison of readability: tag orientation .................................................. 11 1
Figure 6.65 Readability fading ....................................................................................... 112
Figure 6.66 Comparison of readability (I) ...................................................................... l 12
Figure 6.67 Comparison ofreadability(11) ...................................................................... 1 13
Figure 6.68 Comparison ofreadability(111) .................................................................... 113
Figure 6.69 Comparison of readability(IV) .................................................................... 114
Figure 6.70 Comparison of readability(V) ...................................................................... 1 14
Figure 6.71 Comparison Ofreadability(V1) .................................................................... 115

xiv

 

 

 

 

 

Fl

Fll

AIDC

ANI

ASK

BW

CPG

CW

dB

dBm

DBi

DOD

EAS

EIRP

EMI

EPC

ERP

FCC

FDA

FIFO

KEY TO ABBREVIATIONS

Automatic Identiﬁcation and Data Capture
Automatic Number Identiﬁcation
Amplitude Shift Keying
Bandwidth

Consumer Packaged Goods
Continuous Wave

Decibel

Decibels referenced to 1 milliwatt
Decibels referenced to isotropic
Department of Defense

Electronic Article Surveillance
Effective Isotropically Radiated Power
Electromagnetic Interference
Electronic Product Code

Effective Radiated Power

Federal Communications Commission
Federal Drug Administration

First In First Out

XV

FSK

GHz

IFF

IFRB

ISM

ITU

JIT

MHz

MUT

mW

NIST

NRW

OATS

OCR

PSK

Reader

RF

RFID

RMS

Frequency Shift Keying

Gigahertz

Identiﬁcation of Friends of Foe
International Frequency Registration Board
Industrial Scientiﬁc Medical

[ntemational Telecommunication Union
Just in Time

Megahertz

Material under Test

Milliwatt
National Institute of Standard & Technology
Nicholson-Ross-Weir technique

Open Area Test Site

Optical Character Recognition

Phase Shiﬁ Keying

Interrogator

Radio Frequency

Radio Frequency Identiﬁcation

Root Mean Square

xvi

RO

Rx

SAP

SHF

SRD

Tag

TRL

Tx

UHF

UPC

VHF

VNA

WR

Read only

Receiver

Superabsorbent Polymer
Super High Frequency
Short Range Device
Transponder
THRU-REFLECT-LINE Calibration
Transmitter

Ultra High Frequency
Universal Product Code
Very High Frequency
Vector Network Analyzer

Waveguide Rectangular

xvii

i,j

8,8r,£‘0

LIST OF PRINCIPAL LETTER SYMBOLS

Deﬁnition

Distance ﬁ'om transmitter to receiver

Electric ﬁeld strength, in V/m

Magnetic ﬁeld strength, in A/m

Power, in W

Frequency, in Hz

= —1 , imaginary part of complex number

Skin depth

Permittivity, relative permittivity, permittivity in free space
Radiation power conversion efficiency, in percent

Wavelength

Loss tangent ( p = tan (9)

Angular frequency (a) = 2n f ), in rad/S

xviii

 

 

\\

CC

Chapter 1
INTRODUCTION

1.1 Overview

In recent years, the very exciting revolution throughout the supply chain is the adoption
of radio frequency identiﬁcation (RFID) technology. Real time tracking and tracing of
goods and assets in the manufacturing and distribution processes along with other
technologies have been considered as a potential management tool to enhance efﬁciency
of corporate operations and to eliminate counterfeiting. Large retailer chains, government
agencies, manufacturers and research institutes are the main stakeholders in the arena.
Wal-mart, the largest retailer in the world, mandated its biggest 100 suppliers to adhere
RFID tags to cases and pallets delivered to certain distribution centers after January 2005
[1]. Urged by the extremely time-sensitive necessity from retailers and agencies, large
consumer packaged goods (CPG) companies launched into many efforts to implement
RFID system in the supply chain and had their products tagged before the door closed.
Why RFID? Because an RFID- system can give real time, end-to-end visibility and
control of inventory throughout the supply chain. RF ID technology as a inventory
management tool integrates a tangible, physical item actually kept within the facility with
an intangible item existing within the company's record into together without any delay
[2, 3]. In comparison with other Automatic Identiﬁcation (Auto-ID) technologies like the
bar code, RFID is a wireless technology that acquires remote object information often
without line-of—light, which enables efﬁciency, visibility and security of automating data

collection process for both manufacturers and retailers. Products and assets with RFID

technology can be monitored at any time as long as items with tags pass through the
RFID portal systems. Simultaneously, a central database updates the latest status

throughout the company via their computer network.

Anti-counterfeiting is another concern for RFID application. According to an FDA report,
there were 30 counterfeit drug cases initiated in 2003 and this jumped to 58 counterfeit
drug cases initiated in 2004. More counterfeiting drug cases were initiated in 2005.
Therefore, the FDA launched an anti—counterfeiting project advocating item level
tracking to retail packaging of drugs with RFID technology in the US [4]. Philips
Semiconductors and Texas Instruments (TI) Inc. reported in 2004 that up to 7% of all
drugs in the international supply chain may be counterfeit [5]. Hence more manufacturers
have started to enable RFID tags in pallets and box packaging to comply with mandates

from retailers and agencies.

1.2 RFID Puzzles

RFID embraces signiﬁcant potential for the supply chain. However, the implementation
of an RFID system involves many aspects such as infrastructure, interoperability,
frequency, industrial standards and security issue, etc. Many companies impetuously
launched RFID projects and pilot tests to overtake the deadline, even though not quite
comprehending what RFID technology may bring to them. There were numerous reports
and papers regarding RFID application, solution and analysis on various disciplines and
business aspects, for instance, business strategy, the application environment, security
and privacy, etc [6, 7]. Nonetheless, the potential negative effect of packaging and

product contents to RFID performance and stability was addressed as it should be. Even

it was mentioned, optimistic opinions overwhelmed the unsubstantial noise [1, 8, 9]. No
peer-reviewed research was found directly concerned on the effect on RF ID performance
and stability from water content and material dielectric properties. Some RFID system
providers had done a few studies on these issues; however, the research results have not
been based on Design of Experiments (DOE) and peer-reviewed. It is often hard to avoid
bias and misleading statements [10]. From a long term standpoint, low performance and
stability of deployed RF ID systems certainly restrict its fast pace. Impressive research on
the effect of package content, pallet conﬁgurations and temperature to RF ID performance
and stability have been performed in the School of Packaging, MSU [IO-14]. Based on
the previous MSU research, further studies on dielectric properties and power ﬂuctuation

would enhance recognition of intrinsic relations [10].

1.3 Research Aspects

Though robust RF 1D systems work very well in various environments and conditions, the
low power and short range RF lD signal are easily interfered with, absorbed, and/or
reﬂected by surrounding electronic devices, dielectric materials, large amount of metallic
content and even the human body. Thereafter, system performance and stability may be
impacted. In a real environment, the RF ID interrogator (reader) through an antenna
transmits RFID signals that penetrate multiple media, such as wood (pallet), paperboard
(box), and various kinds of packaging material and product content. Further, the RFID
transponder (tag) backscatters the modulated RF signal to the interrogator along the same

path.

With water content from 0% to 100% and water ingredients such as salt, the different
materials Show variable dielectric properties when electromagnetic ﬁelds are applied. To
differentiate the inﬂuence of the amount of water content in any product, a special water
absorbable polymer was used to Simulate a wide range of water concentrations. By
measuring the RF ID power dissipation and dispersion in the path of the RF signal along
with the water concentration, the inﬂuence of water in the product with respect to RFID
performance and stability may be learned. Through measurement of the dielectric
properties of the same samples, the inﬂuence of dielectric properties to RFID

performance and stability may be also proﬁled.

1.4 Research Goals

The preliminary goal of this research is to determine the inﬂuence of water content in a
sample upon RFID signals through measurement of the scattering parameters of the
samples, power loss through the sample and the diversiﬁcation of RFID tag readability
with samples associated with the factor analysis method. A correlation and regression
model interpreted the intrinsic relationship of the RFID system, product content and
packaging Operations. With the restricted statistical analysis, the model of readability and
the results of this research allow industry to predict the feasibility of an RFID system and
optimize the implementation of RFID solutions using speciﬁc products. Recognition of
the inﬂuence of water content in products to RFID performance and stability can help
industry recognize multiple factors associated with successful RFID implementation and

eliminate the negative factors for real RFID implementation.

1.5 Thesis Summary

Chapter 2, Literature Review, presents the RFID primer, electromagnetic principles and
material characterization relative to this research. In addition, the relationship among
water content, superabsorbent and real food products is speciﬁed. Moreover, previous
research relative to this research is reviewed as well. Chapter 3, Methodology, provides
the basic methodology of this research and experimental procedures. Chapter 4, Material
Characterization, particularly describes the experimental method and the computational
process applied to determine the dielectric properties in term of permittivity (e) of
hydrated superabsorbent polymer (SAP) specimens by a vector network analyzer (VNA)
and waveguide at UHF frequencies range from 2.26Hz to 3.0 GHz. Multiple hydrated
SAP samples were measured with water concentration between 45% to 95%, which
Simulated various products with nearly similar dielectric properties and inﬂuence of tag

responses.

Chapter 5, Power Measurement and Readability Survey, shows the experimental
procedure of power measurement and a readability survey in the laboratory. Chapter 6,
Results and Discussion, presents the correlation and the inﬂuence among dielectric
properties, RFID performance and the ﬂuctuation of water content in the SAP samples
according to experiments. Furthermore, the relationship between RF power, attenuation,
tag orientation, antennas style and tag readability are depicted. Chapter 7, Conclusions,
summarizes the new learned results and potential application and proposes future

research and the limitation of this work.

Chapter 2

LITERATURE REVIEW

2.1 Automatic Identiﬁcation Technologies

Auto Identiﬁcation and Data Capture (AIDC) refers to the automatic recognition of data
technologies by barcode scanning, optical character recognition, biometric identiﬁcation
(such as voice, ﬁngerprint and retina), smart card (magnetic stripe and microchip), RFID
etc. AIDC can accelerate the throughput process and eliminate human errors,
consequently. AIDC technologies have been prevalent identiﬁcation solutions in
requiring access control and security applications. Furthermore, AIDC technologies will

make automated inventory control and integrated supply chain management possible [15].

2.2 Brieﬂy History of RFID

Vast and expeditious entity movements in the business world make convenient object
identiﬁcation a necessity. Since the barcode fulﬁlled the identiﬁcation requirement of the
grocery industry in 1970's, squeezing proﬁts from the supply chain became the common
goal. Wireless object identiﬁcation as a potential replacement of barcodes provides a

faster and more accurate identiﬁcation, without line-of-sight.

RFID, which stands for Radio Frequency Identiﬁcation, is a continuously developing
object identiﬁcation technology that began a signiﬁcant growth in the 1980's. The ﬁrst
application of RFID can be identiﬁed as "Identiﬁcation of Friends of Foe" (IFF) for

aircraft to prevent "friendly ﬁre" accidents from dogﬁghts in 1940's [8]. Harry Stockman

ﬁrst introduced the concept of a passive transmitter in his paper "Communication by
Means of Reﬂected Power" [16]. Modern electromagnetic theory related to RFID
application was developed by R. F. Harrington. Subsequently, Kriofsky and Kaplan ﬁled
a patent on primordial RFID, "inductively coupled transmitter-responder arrangement" in
1972 [8]. In 1985, RFID technology was declassiﬁed and came into more common
industry use. In 2003, EPCglobal, a nonproﬁt organization for RF ID technology, released
a recommended RFID standard [9]. In the latest RFID milestone, Wal-mart and the
Department of Defense (DOD) mandated their suppliers rollout RFID technology in early

2005, thereby indicating that RFID was coming into use.

2.3 RFID System Components

A typical backscatter RFID system consists of three main components: transponder,

interrogator and supported software with computer network [17, 18].

2.3.1 Transponder

A microchip based transponder (RF ID tag, see Figure 2.1 left) which generally is a thin,
ﬂexible adhesive label with RFID inlay that can be attached to packaging. An RFID
transponder linked to a conductive coil (tag antenna) receives radiated RF power from the
RF ID interrogator (reader) antenna and simultaneous reﬂects the modulated wireless RF

signal to the interrogator.

 

 

   

Figure 2.1 UHF 915 MHz RFID transponder, reader, and antenna

There are two kinds of transponders, passive transponder without battery and active
transponder with battery. The passive RFID tag is powered by the incident RF signal
exclusively that limits the distance of tag response. Because of this, the price of passive
transponders is much cheaper than that of an active transponder. The price range of
passive RFID transponder is about from $0.15 to $1.00 per item according to
manufacturers and business reviews in the intemet. The price remains fairly expensive
while the read range is shorter than active system. For cost reasons, the passive RFID
solution dominates supply chain applications. Price may continue to decline with the
global RF ID market expanding. If the price would reach a couple of cents per item, RF ID
would be more preferable for corporate use. Besides the price, another limit to RFID

application is that there is no universal industrial frequency or standard.

Depending on the RFID application, information can be written and erased on the
microchips more than one time. Read only (RO) tags have been written so that they have
a unique identiﬁer placed on them in the manufacturing process. The identiﬁer in the
transponder cannot be erased and rewritten at any time which provides unique
identiﬁcation, tamper-evidence and high-level security. Table 2.1 shows the tag classes

classiﬁed by Auto-ID Center, MIT [19].

 

 

 

 

 

 

 

Classes Features Tags Characteristics

Class 0 Article surveillance Passive tags, "Read-only"
Class 1 Identiﬁcation only Passive tags, write once
Class [I Data logging Passive, high security and memory
Class III Environments sensors Semi-passive RFID tags
Class IV Ad hoc networking Active tags

Class V Reader Power class I, II, 111 tags

 

 

 

 

 

Table 2.1 EPC tags classes (Source: Auto-ID Center, MIT) [19]
2.3.2 Interrogator

A RF ID interrogator (reader) transmits a radio frequency signal, providing RF energy to
passive transponders and communicates with each other. The interrogator, through the
antenna, transmits modulated radio frequency waves to the transponders in a speciﬁc
bandwidth [17]. The powered transponders backscatter the demodulated RF signal to the
reader antenna (See Figure 2.2). A computer collects and processes the data via the
network from the reader. A RFID reader can hook-up to multiple antennas to optimize

and maximum coverage [20].

Incident Signal Reﬂected

    

Reader Medium Tag

Figure 2.2 RF ID signal propagation and backscattering

2.3.3 Computer and Backbone Software

The computer software system runs on a computer and/or network, which collects,
processes and stores information in real time. The application software and network are

considered as a part of ERP system in a supply chain [7].

2.4 Basic Principles

2.4.1 Frequency Allocation

RFID systems generally operate in several frequency ranges from LF (125 kHz) to SHF
(5.8 GHz). Different frequencies have various advantages and disadvantages for RFID
operation. High frequencies have longer read range while low frequencies have less
interference from water content and the human body, shorter read ranges and slower data
transfer rates. The radio frequency resources are regulated by the government of a given
country and managed by some international organizations, such as Federal
Communications Commission (FCC) and lntemational Frequency Registration Board of
lntemational Telecommunication Union (lFRB/ITU), respectively. The speciﬁc
frequency within a range such as UHF may run at different frequencies for different
regions due to frequency availability and regulation. RFID systems operating in UHF
(860~96O MHz) are more popular and preferable due to the read range they exhibit (see

Table 2.2). The general RF ID frequency allocation within each ﬁeld is as follow:

0 LF 125~134kHz
0 HF 13.56MHz
O UHF 400~96O MHz

0 UHF 2.45 GHz (S band)

10

O SHF 5.8 GHz (C band)

2.4.2 Near Field and Far Field
In LF and HF, the RF ID system is mainly based on mutual inductance coupling in which

the magnetic ﬁeld produced by the loop antenna coils rapidly drops off with distance

(1/ 1" 3 ) in free Space (see Figure 2.3). R is the distance for the path of the signal. The

attenuation of a magnetic ﬁeld limits the read range for all passive RFID devices [21].

y
r

Magnetic Strength (8)

 

A

Datum (r) T

Figure 2.3 Attenuation of magnetic strength vs. distance in near ﬁeld region

At UHF, the RF ID transponder and interrogator communicate in both the near ﬁeld and
far ﬁeld, which allows broader read ranges and a faster data transfer rate (see Table 2.3)
[17]. Near ﬁeld refers to a region generally in close proximity to the radiation source
where the electric and magnetic ﬁelds do not indicate a completely plane wave
characteristic, but alternates considerably from point to point [22]. The near ﬁeld is
ﬁirther split into the reactive near ﬁeld region which is the nearest to the radiation source
and accommodates most or nearly all of the stored energy, and the radiating near ﬁeld
region where the radiation predominates over the reactive ﬁeld but lacks substantial

plane-wave character [22]. In the near ﬁeld, both the electric ﬁeld (E) and the magnetic

ﬁeld (H) are relatively static, without propagation. Maxwell had proved that beyond the
quasi-static near ﬁeld, both the electric ﬁeld and the magnetic ﬁeld, at a certain distance,
detached themselves from the conductor and propagated into free space as a combined

wave at light speed with a constant ratio of: E / H =1207r = 3770 [22].

The critical point at which separation happens is called the far ﬁeld. This ﬁeld has a
predominantly plane-wave characteristic. Electric ﬁeld strength and magnetic ﬁeld
strength are represented in transverse planes normal relative to the path of propagation
are separated distributions. In far ﬁeld, the transmission power of the propagation RF

signal attenuates as the inverse square of distance.

S = Pl (Equation 2.1)

47172

 

where, S is signal strength at a distance r from the source and Pt is transmission power.
The farther the RFID transponder is from the interrogator, the less RF power could be
received from the interrogator. 1f the distance is less than 1/20th of a wavelength, it is in
the near ﬁeld; if the distance is longer than 5 wavelengths, it is generally in the far ﬁeld
(see Table 2.3). Therefore, at UHF, transponders operate both the far ﬁeld and transition

ﬁeld (between the far ﬁeld and near ﬁeld) [17, 23].

 

 

 

 

 

Name Frequency range Near ﬁeld region Far ﬁeld region
LF 30K-3OOK <120m >12km
HF 3M-3OM <1m >110m
UHF 300M-3G <1 .65 cm >1 .65m
SHF 3G-30G <0.25 cm >0.25 cm

 

 

 

 

 

 

Table 2.2 Near ﬁeld and far ﬁeld regions

2.4.3 Read Range and Power Assumption

Read range is the maximum distance that the RFID interrogator and transponder can
communicate with each other [18]. Read range is an important speciﬁcation and
characteristic of an RFID system. Active RFID transponders have longer read ranges
compared to that of passive RFID transponders that are completely powered by the
received RF energy. The actual read range depends on the ﬁ'equency, both antenna
designs and the effective isotropically radiated power (EIRP) [15, 21]. Within this read
range, the RFID transponders receive enough RF energy and power up the integrated
circuit to backscatter the modulated signal to the reader (see Figure 2.2) [24]. LF and HF
RFID systems are based on inductive coupling, such as the TI-RFID running at 13.56
MHz. The read range of this kind of RFID system is no more than a few inches. Read
ranges of ultra high frequency RFID systems, for instance 915MHz, are more than
several feet, which is based on electromagnetic backscatter coupling. This system is also

called a long range system vs. the forward Short range system [17].

There are two ways to increase the read range. One is to increase the transmission power
and the other is to decrease the minimal threshold operating power required by the
transponder or increasing the power conversion efﬁciency [24]. Recently, technology has
dropped down the minimal required operating power to the range of 0.5-1 mW, and even

lower [25]. The power conversion efﬁciency nis about 20%, therefore, the minimum

required power for the tag Integrated Circuit (IC) is about 0.1~0.2 mW. The antenna can
radiate energy up to 4 watts EIRP in the UHF range, see US FCC Part 15-45 [26].
Theoretical read range is longer than real read range. Read range can be calculated using

the Friis free-space formula, notice it is assumed that the read range is in free space.

13

 

2
_ 2 PthGr(l—|s| )
ax _ 47: Pth

where, xi. is the wavelength, Pt is the power transmitted by reader, Gt is the transmitting

 

 

r m (Equation 2.2)

antenna gain, Gr is the tag antenna gain, Pth is the minimum threshold power to power

up the tag, and |S|2 is power reﬂection coefficient at the tag resonant frequency. Pth is

the EIRP [27]. Power or current gain can be expressed as a decibel (dB) value. The dB

value is calculated by taking the log of the ratio of the measured power with respect to a

 

reference power multiplied by 10 (dB = 10mg10 £3144, dBm = 10 log 5,02% ).

In

2.4.4 Modulation

Radio frequency communication transmits and receives data through modulating a carrier
wave. There are three digital modulations: Amplitude Shift Keying (ASK), Frequency
Shift Keying (F SK) and Phase Shift Keying (PSK). Each of them has different power
consumption, bandwidth and reliability (see Figure 2.4). In time domain, the carrier,

Sinusoidal signal can be expressed as:
v(t) = Acos(a)t + 45) , a) = 27: f (Equation 2.3)

Each of the three variables, amplitude A , angular frequencyw , and phase ¢can be

applied to different modulation techniques [28].

I4

HFSK mode

ll]

     

4.44-1-

 

 

Figure 2.4 F SK and PSK digital signal modulation

In passive RFID systems, power reﬂected from the tags is neglectable in comparison
with the power radiated from the reader. Consequently, the reader might not able to pick
up the coupled response from the tags. A low frequency subcarrier modulated within the
RFID system can avoid this from occurring. For an RFID system with a carrier frequency
of 13.56 MHz, the subcarrier frequency could adopt 847 KHz (1/16), 424 KHz (1/32) or
212 KHz (1/64). This depends on the data transfer rate required in the application, and

standards for the system. [17]

2.5 Electromagnetic Properties

2.5.1 Dipole Moment and Molecular Polarity

According to molecular polarity, molecules can be classiﬁed as polar and nonpolar. The
polar molecules possess an electric dipole moment in lowest energy-level in comparison
with nonpolar molecules [29]. Chemical bonds, van der Waals attraction, and repulsion
forces are considered distinguished interaction forces over short ranges, while dipolar

interaction forces have a very long range. Polar molecules examples are HC1 and CO and
whereas non-polar molecules examples are H2 and 02. The easy way to recognize each

type is whether the molecules have a point of symmetry. Triatomic molecules, for

instance H20 (see Figure 2.5 ), are polar unless three atoms lie on a straight line with a

direct line from O to the 2 H atoms [29].

Figure 2.5 Orientation of atoms and direction of the electric dipole relative in H20

Molecular dipole moments in gaseous state and in liquid state are different. In a liquid
state, the dipole moment is considered as consisting of a continuous medium with
dielectric. In liquids, the average energy of a single dipole is the same in all direction
because a liquid does not possess any preferential direction and the neighboring
molecules do not form an orientation. In a solid, the average potential energy of a
molecule is contributed to crystalline ﬁeld acting on the dipoles normally depends on
temperature. The direction of dipole relative to the crystal axes in a crystalline solid
determines the average potential energy of a polar molecule. When the average energy of
molecules doesn't reach a relative minimum, the molecules can't rotate freely until the

average energy breaks the equilibrium [30].

2.5.2 Dielectric Permittivity

Permittivity (e) of a dielectric substance describes quantitative characteristic of any
electric ﬁeld affected by the dielectric substance, which presents the polarized ability of
the substance to an applied electric ﬁeld. In comparison with electrical conductivity (0'),

it relates to charge in isolation rather than current. When a voltage is applied to dielectric

l6

substance, if there are no free charge carriers, such as electrons and ions, the substance
tends to pass current; the voltage source provides the energy to move charge. The charge
that displaced is restricted by the polarity of molecules in the substance. Permittivity is a
complex, frequency-dependant quantity with the real part and imaginary part, expressed

as,
g = g] i 132 (Equatron 2.4)

the real part, Re( 8) presents the propagation characteristics of the energy. The imaginary
part, Im(E ) referred to as loss factor represents energy loss in the substance due to
polarization of molecules [22]. The Sign of the imaginary part is dependant on the

numeric Sign conversion. The dielectric permittivity of free space 50 is 8.85x10'12 F/m.

Permittivity is usually given as the ratio of that of free space, known as relative

permittivity or dielectric constant (er) which is frequency dependent in parts of

frequency range and dimensionless. Relative permittivity of free Space is deﬁned as 1,
relative permittivity of air is about 1.0005 and relative permittivity of water is
approximately 80. Higher permittivity of substances stores greater charges with the same
applied electric ﬁeld. As a result, the substance has higher capacitance. For most
materials, dielectric constant depends on temperature, frequency, atomic structure, and

salinity of the material [29].

17

A

Figure 2.6 Complex permittivity and loss tangent (tan 5 = 52 / 31 )

2.5.3 Loss Tangent

The loss tangent (p) deﬁned as the ratio of dielectric loss factor (52) to dielectric

permittivity (6]) (tan 5 = 82 / 81 ) and, is roughly, wavelength independent. Loss factor

is a product of the dielectric constant and loss tangent (see Figure 2.6). High or low
values of loss tangent of the substance impacts the penetration of radio wave with the
substance, and the radio absorption length. When a radio frequency wave penetrates into

the dielectric substance, the wave ﬁeld strength attenuates exponentially with depth. For

example the distance where the ﬁeld strength decreases to e'1 is the skin depth 5 .

5 = 2/(0/100' (Equation 2.5)

2.5.4 Dielectric Absorption

Dielectric absorption indicates the conversion of electromagnetic energy into heat energy.
Dielectric absorption has a few mechanisms: relaxation effects associated with permanent
and induced molecular dipoles and resonance effects occurred in the rotations or

Vibrations of atoms, ions, or electrons [31]. Dielectric relaxation occurs in insulating

l8

materials with negligible or small electrical conductivity. Polarization relaxation occurs
in the high dielectric constant substances. Absorption of the ﬁeld's energy leads to energy
dissipation. The mechanism of dipoles relaxing is called dielectric relaxation and, for
ideal dipoles without dampening, is described by classic Debye relaxation [31]. As
mentioned in section 2.5.1, polarity of a molecular structure and ionized molecules solicit
energy dissipation to change the moments of polar molecules in applied electromagnetic
ﬁelds. The traits of RF absorption in dielectric substance represents the electromagnetic
properties. Dielectric permittivity and loss factor generally represent the material’s
electromagnetic properties. Radio frequency waves propagate in a straight line in free
space. They may be reﬂected, transmitted or absorbed by dielectric substances in the path.
Products, such as foods or drugs with water content, absorb RF energy and transform it
into heat. A typical example that describes this process is a microwave oven in the

kitchen.

2.6 Water Content in Foods

2.6.1 Water Activity

Foodstuffs and medication materials contain water. As a polar molecule, water can be
partly aligned by an applied electric ﬁeld; however, there are forces in water preventing
its molecules from moving freely. Thus, the energy counteracting this resistance is
transferred to the ions and then to neighboring atoms or molecules. Food products or any
material containing such charged ions are able to interact with any electric ﬁelds. Water

absorbs radio frequency energy and turns it into heat [32].

19

Water content is a very important factor in determining food quality, shelf stability and
textural properties. Natural moisture content in produce offers freshness and quality. The
crisp, fragile biscuit or one in a limp state are determined by the water content and its
distribution within the biscuit. To maintain the special textures and ﬂavors in a food
product, the food ingredients strictly limit the water content and distribution within the
food product. Controlling the water activity and reactivity with unbound water content in
food product will really help to attain food stability. In spite of the microstructure, local
viscosity and associated molecular mobility are very important to food stability.
Nevertheless, moisture content is the one of key factors to determine these parameters of
a food matrix [33]. To extend the shelf life, adjusting the water content is a common
approach. Sublimation or evaporation is often used to remove liquid water to enhance the

product stability [34].

2.6.2 Water Forms

The water molecules in foods appear in different forms depending on surrounding
molecular environments, generally in forms that have different physiochemical properties

as follow:

1. Free water. Water in this form that is enveloped by other water molecules only.

The physicochemical properties are the same as these of pure water.

2. Capillary water or trapped water. Water in this form is enveloped by a physical
barrier or retained by tiny channels. The physicochemical properties are the same

as those of free water due to normal water-water bonding in this form.

20

3. Bound water. Water in this form is partly enclosed by other food components in
molecular contact, which leads to a signiﬁcant difference in physiochemical

properties compared to free water.

Due to different bonding existing in foods, they are considered as heterogeneous mixtures
from the standpoint of chemistry, though the macrostructure of the food material may be

homogeneous [35, 36]

2.6.3 Dielectric Properties

The state of water in a food substance lies in the degree of interaction between water
molecules and the glassy solid pertaining to hydrogen bonding. Lechuga-Ballesteros et al
found that the proportion of high mobility water molecules at 1 GHz increased for
hydration levels above the hydration limit [37]. Thus, more water molecules are relatively
free to respond to applied electric ﬁled and showed a dipole moment near to gaseous
water molecules due to hydration-induced conformational changes. The dielectric

parameter increases is proportional to the increasing of water concentration in the foods

[37].

The amount of water content in a material greatly affects its electromagnetic properties
[38]. Water has a high dielectric constant at room temperature (see Table 2.3). Dry
materials have low dielectric constants often less than 10. Therefore the percentage of
water content in the substance is indicative of the dielectric properties. A high water
percentage usually shows proportional increases of the loss factor of the substance and a
high dielectric constant. The dielectric constant of a mixed substance commonly is based

on its components and stands between the medial of its components. Dielectric loss has a

21

complicated transaction mechanism. For example, it may increase 20~30% with raising

the water content percentage of the substance, and then decrease rapidly [3 8].

 

 

 

 

 

 

 

 

Substance Dielectric constant Loss factor Loss tangent
Water 80 12.5 0.16
Mashed potato 65 22.1 0.34
Cooked ham 45 25.2 0.56
Peas 63 15.8 0.25
Most Plastics 2~4.5 0.002~0.09 0.001~0.02
Woods l.2~5 0.0l~0.5 0.0 1~0.1
Papers 3~4 0.15~0.4 0.05~0.l

 

 

 

 

 

 

Table 2.3 Dielectric properties of foodstuffs and other packaging materials at 2.45GHz
and 68°F (Source: Sacharow, et al: Microwave Packaging [38])

2.6.4 Gel Structure and Food Biopolymers

Gel structure refers to the crosslinking of long polymer chains to shape continuous three
dimensional networks that retain ﬂuid. Many food biopolymers form gels. Such networks
and structures consist of carbohydrates, protein and lipids. Retained water within the
networks and structure is not permanent, and depends on environment conditions such as
temperature, shear and maintained by the bonds within the structure [33]. The mechanism
of retaining water in a food biopolymer and the superabsorbent polymer that will be
described in later sections are similar. Hydrated superabsorbent polymers can be used to

simulate the water behavior and properties as found in food biopolymers.

22

2.7 Superabsorbent Polymer

2.7.1 History of Superabsorbent

Superabsorbent polymers (SAPS) are hard, dry, granular powders with a white or slight
yellowish color. Generally, I g of dry, ﬂuffed, cellulose pulp ﬁbers will take up to 12 g of
water, whereas 1 g of SAP may retain up to 1,000 g of water (see Figure 2.7) [39]. In
1970, Weaver developed the ﬁrst uncrosslinked starch graft polymer at the Northern
Regional Laboratory of the US Department of Agriculture. Japan was ﬁrst to
commercially manufacture a superabsorbent polymer in 1978. SAP was used in infant

diapers in Europe in 1980 [39].

Polyacrylic acid is the primary polymer for superabsorbent polymers today. The swollen
gel holds the ﬂuid in a solid, rubbery state and locks the ﬂuid from leaking out of the

polymer.

 

Figure 2.7 Hydrated superabsorbent polymer sample, with more than ten times of its
weight of water absorbed by the SAP particles

23

2.7.2 Structure and Properties

Water-swellable superabsorbent polymers are synthesized by free radical crosslinking
polymerizations of hydrophilic acrylate monomers in suspension of the aqueous solution
in a hydrocarbon [40]. The swelling capacity and gel modulus of SAP are controlled by
the crosslinkers. The new gel like polymerized product is dehydrated in a continuous
oven, and then milled to the desired particle sizes to form free-ﬂowing powder or a
granule polymer. SAP is widely used in absorbing and retaining water and body ﬂuid in
personal hygiene product, droughty planting and moistureproof products, such as infant
diapers, agriculture mulches and biosorbents in preparative chromatography. SAP
particles tend to swell quickly when they osculate with water or ﬂuid, whereas saturation
or equilibrium swelling comes much later [40]. Swelling capacity is related to the
properties of the network. By increasing the crosslink density of the gel particles, ﬂuid
retention may be enhanced under shear. It is more rigid in the swollen status; however, it
does not condense the equilibrium swelling capacity. The chemical structure of
polyacrylic acids is shown in Figure 2.8, where there is an ionizable group on each repeat
unit (-COOH). Crosslinking occurs at the —OH bonds in the polymer chains. Minor
crosslinkers act in a primary role for attaining the preferable swelling property of
superabsorbent polymer in addition to modifying the swelling and mechanical properties

[39, 40].

-[-CH2- 5““
OOH

Figure 2.8 Crosslinking structure in a superabsorbent polymer

24

2.7.3 Mechanism of Water Absorption

Binding water in the SAP is not a chemical reaction. The hydrated superabsorbent
polymer is rather a mixture instead of a new chemical. Retention of water in SAP is
similar to cotton. Water diffuses on the long chain molecules that are like the long cotton
ﬁbers, while cotton ﬁbers suck up water by convection. These ﬂexible polymer networks
carrying dissociated ionic hydrogen groups are the most efficient water absorbers. When
water diffuses into the SAP particles, SAP inﬂates to accommodate the additional water
molecules. Crosslinked networks in SAP molecules prevent it from dissolving in the
absorbing ﬂuid. The hydrated superabsorbent mixture in equilibrium is considered an
isotropic, homogeneous (ideally) dielectric material. The dielectric properties and water
activity may comply with the rules as mentioned in this chapter. There are a few of
literature sources on superabsorbent polymers which related mechanism of swelling,
swelling capacity, cross-linking in SAPS, application, and manufacture etc, please see

[3941].

2.8 Previous Research

2.8.1 RFID Application

Clarke and Tazelaar (2005) found that tag orientation and product type had a signiﬁcant
effect on tag readability based on his research on a pallet load having Matrics 915 MHz
Class 0 RFID tags. Moreover, the tier, column and row of tagged cases also had an effect
on tag readability [7, 10, 18]. Jonson (2005) presented a RFID tag failure mode with class
0 RFID transponders using ASTM Vibration and impact procedures to evaluate the

robustness of the RFID tags in simulated transportation status. The results showed shock

25

and drop impact damaged the transponders. Nonetheless, Vibration did not affect the
ﬁinction of tags. However, tag placement was another inﬂuential issue in the failure
mode. Transponders adhered perpendicular to the corrugated ﬂuting have a signiﬁcant
failure level compared with those adhered parallel to the box ﬂuting [13]. Ryan (2002)
described a model for implementation of a RF ID system into a warehouse environment
that offers companies an unbiased method in the form of decision trees which are based
on how packaging is tracked through the warehouse [12]. Onderko (2004) found that a
HF RFID system running at 13.56 MHz had higher stability for data transmitted through
a package of ﬁ'ozen beef. However, those systems operating at 915 MHz encountered a
loss of data when transmitting in the same situation [1 1]. Clarke and Vorst (2002) found
that RFID tags might affect the quality and consumer acceptance of beef products [42,
43]. Ramakrishnan (2005) provided a set of benchmarks for comparing the performance
of UHF passive transponders, which revealed the current state of commercial RF ID tags
[44]. Ramchandran, A R (2004) described a type of plant scanner with a handheld PDA
(personal digital assistant) using RFID tags for child Visitors to the Michigan 4-H
Children's Garden. The visitors can instantly receive the plant background knowledge
from remote server where they approach a plant in the garden [45]. Weis (2003)
identiﬁed several potential threats to security and privacy and proposed several efﬁcient
security mechanisms in his research [19]. Hardgrave et al, at the University of Arkansas
suggested that RFID reduced the out of stocks through investigation of 24 Wal—mart store

in a study [46].

26

2.8.2 Material Characterization

Janezic (2003) presented nondestructive relative permittivity and loss tangent
measurements for several dielectric materials using a split-cylinder resonator, which were
in good agreement with other methods [47]. Bogle (2004) developed a material
characterization measurement technique for highly reﬂective or lossy material using a
partially ﬁlled rectangular waveguide [48]. Meeusen (2004) discussed the identiﬁcation
of errors in the extraction of the electromagnetic properties of a material using an X-band
waveguide system. In addition, the results showed the factors with respect to the
uncertainty of the dielectric properties in terms of permittivity relies on the
electromagnetic properties of the material sample [49]. Killips (2004) presented classical
mixing approaches to determine effective electromagnetic properties of a two-phase
mixture. The same formulations were calculated in relative permittivity with the
measured data. However, there were some differences between these parameters due to

the interaction between particles that was evident in magnetism [50].

2.8.3 Material

Hoepfner (2001) presented the inﬂuence of dielectric permittivity to the microstructure of
material, the relative dielectric permittivity and Q factor of the material had a signiﬁcant

variety with different relative density [51].

2.9 Relevancy

Previous research and literature information discussed in this chapter provide valuable
hints and relevant measurement procedures for the research conducted in this thesis. It

succeeds to the methodology of material characterization and RFID tag readability survey

27

speciﬁed in this chapter. However, due to the different research goals in those research,
creative procedures are speciﬁed for our purpose in this thesis which describe in Chapter

3 Methodology and other chapters.

28

Chapter 3
METHODLOGY

3.1 Introduction

This chapter describes experimental and numerical techniques to extract constitutive
dielectric parameters of homogeneous hydrated superabsorbent polymer (SAP) samples
placed in a WR340 waveguide using HP8510C vector network analyzer. Furthermore,
data acquisition technique was applied to measure power gain near the RFID
transponders and RFID tag readability with distinct reader antenna styles and
conﬁgurations. The hydrated SAP sample was placed in sample window with the
thickness 20 mm. The RFID transponder and antenna of power sensor were placed

behind the sample.

Testing and measurement procedures, experimental setup, sample preparation, calibration,
extraction processing will be explained in the next chapter. The following sections
presented the principles of performing the dielectric properties measurement, RFID
power measurement and tags readability survey. The results and analysis for hydrated
superabsorbent polymer with water content from 55% up to 95% will be reported in the

chapter 5 and chapter 6.

There are typically several steps to measure the complex constitutive dielectric

parameters:

1. The linear, homogenous and isotropic sample is prepared and placed in the testing

equipment.

29

 

2. Vector network analyzer (VNA) measures the scattering parameter (S-parameter)

with the connection to the testing devices through transmission/reﬂection technique

[52-54].

3. The complex dielectric constitutive parameters in term of permittivity and
permeability are able to be extracted from the experimental scattering parameters
using an extractor with an iterative complex Newton's root-searching algorithm or

the Nicholson-Ross-Weir (NRW) method [48].

In comparing with material characterization, the power measurement and readability
survey were pretty straightforward. The sample was placed in a sample window between
the interrogator and transponder, with data acquisition program, power sensor and
Alien® RFID Gateway. The average power can be acquired from a 2-wire folded dipole
antenna (see Figure 3.1) connected to a power sensor, from which was placed in the same
location and orientation with RFID transponder behind the sample and saved into a data
ﬁle by LABVIEW program. Meanwhile, the readability of RF ID transponders placed in
the same position will be recorded into data ﬁle through Alien® RFID Gateway software.

Tests were repeated and recorded with different tag orientations, antenna style and

FHA/2:163 cm—g

ll

Figure 3.1 Dimension of 2-wire folded dipole antenna [17]

distance.

 

30

Experimental scattering parameters measurement using NRW technique can rigorously
characterize dielectric properties in comparing with these theoretical values [48]. The
result of power measurement and instantaneous RFID tag readability on same SAP
sample associated with dielectric properties in term of permittivity provide coincident
correlation among intrinsic dielectric properties of the substance, average antenna

receiving power, RFID tag performance and stability.

3.2 Product Simulation

The dissipation and dispersion of radio frequency energy in material are affected by
multiple factors, such as molecular structure, loss tangent and signal frequency. Suppose
that linear, physically homogenous isotropic samples in which water concentration is the
exclusively variational factor that determines the pattern of component proportion of the
sample were existed, meanwhile, the other component in the sample has enough
ﬂexibility and network to lodge water content that normal water-water hydrogen bonds
were dissociated to form new bonds between water and the other component. If that is the
case, whatever water concentration were diversiﬁed, the water is free water. Thereby
physicochemical properties and electromagnetic absorption spectra of water in the
samples are similar to these of free water. That differentiation of dielectric properties in
these samples is depending on the water concentration. Obviously, with controlling the
hydration process of samples, we would be able to perform measurements of material
characterization and differentiate impact by the water content exclusively besides the
potential minor effect factors, such as density, hydration time etc. Water in hydrated

superabsorbent polymer (SAP) presented these characteristics.

31

Thereafter, a wide range of products with one independent variable — water content using
unique SAP particles can be simulated. The dielectric properties of the new SAP-water
mixtures would be similar or near to the food products with which have the same water

concentration.

3.3 Measurement Description

The experimental specimens in this thesis were hydrated SAP mixtures. The SAP
exhibits large capacity of water absorbency. Due to its crosslinked network structure,
SAP is easily mixed with aqueous ﬂuid to puff up long chain structures to lodge the water
molecules. Water absorbed by this polymer keeps its physiochemical properties and
electromagnetic absorption spectra [40]. Based on these properties, the superabsorbent
polymer is low cost and practical material to simulate real products with certain amount

of water content.

 

Figure 3.2 Hydrated SAP mixtures in the sample window

The SAP mixtures with holding 45% to 95% by weight water content were measured,
four different trials were performed. The dielectric properties of the mixtures with 55%,

60%, 65%, 70%, 75%, 80%, 85%, 90%, 95% water content respectively were reported in

32

this thesis. The thicknesses of the samples ﬁlled in the waveguide were 12mm and 7mm
respectively. (See Figure 4.5) The sample thickness in power measurement was 20mm.
the width and length of sample window in power measurement is 170mm*l70mm.

Figure 3.2 showed the measurement window and sample in the measurement.

Since the dry SAP has a low dielectric constant, very little loss and no magnetic
properties. Water is a high dielectric constant material, it was expected while water
concentration increasing, the measured permittivity would increase as well. The result is

listed in Chapter 6.

3.4 Superabsorbent Speciﬁcations

Corn starch/Acrylamide/ Sodium Acrylate Copolymer are classiﬁed as starch graft
polymer (2-propenamide-co-2-propenoic acid, sodium salt). The commercial name is
Water Lock A-100, was packaged in 20 kg multiwall paper bag with polyethylene liner
stored in a low humidity conditioning room. Water lock A-100 superabsorbent polymers
are tan, free ﬂowing powders can absorb and/or immobilize large quantities of aqueous
ﬂuid, at neutral or alkaline pH. More than 98% particle size of the polymer is less than 20
meshes. l g of the polymer can lock as much as 175 ml distilled water and 60 ml 1%
NaCl solution. The polymer absorbs water and becomes very slippery when wet. The

manufacturer is Grain Processing Corporation, Muscatine, Iowa 52761 [55].

3.5 Specimen Preparation

Isotropic and homogenous properties are the basic requirement for the measurement to

determine the electromagnetic characteristics. The hydration of SAP particles is the

33

critical process to form consilient samples. SAP particles tend to puff up rapidly when the
surrounding environment is aquatic whereas saturation swelling comes much later [40].
On the other hand, big capacity of water absorption and deﬁciency of water is a pair of
contradictions in making samples in low water concentration. Well-blended sample,
uniform density and glabrous surfaces of samples are the major treatment to eliminate the
potential sources of error and measurement deviation in the measurement procedures.
Particle blender and well-proportioned water supply can make the uniform water and
particles distribution. When SAP samples are stored in containers, it is common practice
to wrap up the samples and containers to prevent the evaporation of water. Calculation of

water concentration in the sample is discussed in the next section.

3.6 Determination of Water Content

When determining the water content in the sample it is important to prevent any loss or
gain of water or particles in blending. For this purpose, excessive water supply
ﬂuctuations should be avoided. The water content of superabsorbent polymer is

determined by the following equation:

 

m
Wt% = W X100 (Equation 3.1)

mtotal

 

Wt% = mtotal - minitial X100

m (Equation 3.2)

total

Where, mw is the mass of the water, mmml is the mass of hydrated superabsorbent

polymer mixture. The water content of superabsorbent polymer can be determined

34

accurately by measuring mass of water molecules present in a known mass of sample.
According to the above equations, practically, by measuring the total weight of SAP
sample after absorption equilibrium and measuring the total weight of water absorbed,
the weight percentage can be calculated, versus versa, the weight percentage can be
calculated by measuring the total weight of SAP sample after absorption equilibrium and
measuring the initial weight of SAP particles. It assumed that no new bonds formed
between water molecules and SAP molecules while water infused in SAP and water is

free water in the mixture.

3.7 S-Parameter Measurement

A vector network analyzer (VNA) model HP 8710C operating in the transmission/
reﬂection mode connecting with a WR340 waveguide was used for the measurement of
scattering parameters, S11, S22 and 812 ,S21 over ﬁ'equency range from 2.2 GHz to 3.0
GHz with resolution of 4 MHz which covered the frequency allocation of 2.45GHz (S-
band) RF ID application. A total 201 points were swept over the frequency range. The
data were saved in a ﬂoppy disk and then transfer to PC. Figure 4.1 to Figure 4.8 showed
the VNA, waveguide, calibration set, sample holder, sample ﬁlled in holder and signal
transmission and reﬂection diagrams. The experimental results showed the frequency
responses VS.S11 ,S22 and S12 ,SZI respectively in Chapter 5. These ﬁgures presented
that water concentration is a suitable parameter for SAP dielectric characterization in
term of permittivity, since the responses are well deﬁned and visibly apart for SAP
samples with 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90% and 95% of water content

from 2.2GHz to 3 GHz in the measurement.

35

3.8 Power Measurement

The objective of power measurement was to determine the effect of highly lossy water on
the RFID readability. A 2-wire dipole antenna connected to a power sensor and placed on
the backside of the sample window captures the RF signal radiated from the RFID reader
that was placed on the other side of the sample window. Besides the sample widow, the
two Sides were separated by the Aluminum shield template. Presumably, the only path for
RF ID signal radiating was the sample window. The power level comparison of the

shielded area and unshielded area is listed in chapter 6.

Alien® circular and linear reader antennas were in measurement. Fourteen locations were
measured at the distance of 1cm, 5cm, 10cm, 15cm, 20cm, 25cm, 30cm, 350m, 40cm,
45cm, 500m, 550m, 60cm and 65cm respectively. Two kind of tag orientation, horizontal
to reader antenna and vertical to reader antenna were measured. The results are listed in

chapter 6.

3.9 Readability Survey

The Alien squiggle UHF RFID tags were place in the same location with the antenna of
power sensor. Theoretical, the transponder in that location and the receiving antenna of
the power meter were radiated the same level of RF power from the reader antenna that
located in the other side of the sample window. Two antennas have different radiation

power conversion efﬁciencyn [l 7]. However, normalized power reads from power sensor

were equivalent to the received power of the transponder antenna at the same location,
incurred in the same time and with the same orientation. Under the circumstance, the

readability of the RFID tag with corresponding conﬁguration and the power reads

36

showed some correlation and intrinsic relationship. Therefore, a consistency model could

be proﬁled by linking these measurements.

37

Chapter 4
MATERIAL CHARACTERIZATION

4.1 Material Characterization

Network analysis technique involves the measurement of incident, reﬂected and
transmitted electromagnetic waves that pass through the transmission medium. For fully
characterization of a linear network, it is necessary to measure both magnitude and phase

of components.

Vector network analyzer (VNA) system measures the magnitude and phase characteristic
of network and of components. VNA and a closed waveguide, which measure S-
parameter are commonly used instruments for the measurement of dielectric properties
and material characterization [56]. The S-parameters are measured with constitutive
parameters may be determined using the NRW experimental technique. According to
Nicholson-Ross-Weir (NRW) technique, the sample under the measurement should be
linear, isotropic homogenous samples with parallel ﬁont and back surfaces [48]. In this
thesis, the SAP specimens infused with variable water content measured in the frequency
range of 2.2GHz~3.0GHz using a WR340 waveguide were subject to the restriction. In
the measurement, scrupulous preparation process and stringent physical treatment method

were taken to improve the accuracy of measurement.

38

4.2 Measurement Equipment

4.2.1 Vector Network Analyzer

Network analyzer measures the magnitude and phase characteristic of material under
testing (MUT). The basic principle of network analyzer is simple. Signal source
controlled by the network analyzer generates an incident Signal and applies to the test
network and component. The network analyzer contrasts the reﬂected signal from the

MUT or the transmitted signal through the MUT.

 

 

 

 

 

 

 

 

 

 

 

Figure 4.1 HP-8510C Network Analyzer and panel block (Courtesy of Agilent Corp.)

4.2.2 Waveguide

The WR340 waveguide (where WR Stands for “waveguide rectangular” and 340 refer to
the inner waveguide dimension 3.4 inches) has low attenuation, good operational
bandwidth for single-mode propagation and good mode stability [57]. Below the
designated frequency range and cutoff frequency, attenuation of waveguide augments
quickly tending to inﬁnity. Waveguide material is aluminum or brass (copper alloy). The

detail Speciﬁcation is listed in Table 4.].

The cutoff frequency of the waveguide is given by:

39

Lower: fa,

c _ 2.9979 x10'0cm/s

”17 = 2a _ 2x2.54x3.4cm

z 1.736GHz, Upper: 2x ﬂ 1M, z3.47GHz

where, a is the length of cross section (see Figure 4.2 right) and c is the light speed.

 

 

Designation Freq. Cutoff Guide Inside Wall
Range Freq. Wavelength Dimension Thickness
WR340 2.2-3.3 GHz 1.736 GHz 6.83 in 3.40‘1.70 in 0.08 in

 

 

 

 

 

 

 

 

Table 4.1 WR340 waveguide characteristics [23]

 

 

Figure 4.2 WR340 waveguide components and cross section (Courtesy of Penn
Engineering Components)

4.3 Experimental Setup

The instruments and experimental setup of electromagnetic characterization of the
hydrated SAP sample were shown in Figure 4.1~Figure 4.4. A WR340 waveguide was
connected to an HP 8510C Vector Network Analyzer via coaxial cables (See Figure 4.3).
The brass waveguide sample holder used to measure the S-parameters is shown in Figure
4.4. The thickness of sample holder is 1.0 inch. The sample holder is connected to the
waveguide WR340 with eight precision alignment screws to minimize the discontinuities
across the interfaces and reduce the uncertainty measurement errors. The brick base

should be in the same ground plane to ensure two waveguide sections to be placed in the

40

same horizontal plane. The coaxial cables must be spatially stabilized without any

movement while calibrating and measuring samples (See Figure 4.3).

Before measuring any test sample, a standard baseline was checked to further validate the
experimental setup. After performing the calibration, the two waveguide sections were

placed together and the magnitude and phase of the S-parameters was checked to ensure

. - CXP ~ - . .
that 5:32 z 1" 10 and 511,22 ~ 0‘ 10. Meanwhile, an extractron was performed on

the S-parameter measured from the empty sample holder to ensure a free space baseline

for the system.

4.4 Calibration Processing

lmperfection of test equipment and test procedures leads to systematic errors. In radio
frequency network measurement, systematic error is the most Signiﬁcant factor of
measurement uncertainty [49]. Systematic error is unable to be removed from
measurement. We can characterize and eliminate the systematic errors through
calibration procedures and mathematical model optimum during the measurement
process. Repeatable systematic errors will be greatly reduced and the accuracy of
calibration standard will be able to transfer to the measurement of the device through

standard calibration procedure [58].

The process of eliminating uncertainty at S-parameter measurement within the network
analyzer and waveguide system was named as measurement calibration. Some special
procedures and scrupulous considerations for calibration and measurement must be
performed using network analyzer to acquire accurate data. The required and common

calibration and measurement techniques used in a HP8510C vector network analyzer

41

were discussed in this chapter. The frequency range of WR340 waveguide system is
2.2GHz to 3.3 GHz, sweeping frequency range in the measurement was 2.2 GHz to 3.0

GHz; hence, the frequency span was 0.8GHz.

 

Figure 4.3 VNA and WR340 waveguide set-up

4.5 Measurement Calibration

Transmission and reﬂection measurement general utilize vector accuracy enhancement
technique to cut down the systematic errors and remove error contributions. The basic

steps of the calibration techniques:
1. Measuring the magnitude and phase response of standard device.

2. Estimating model coefﬁcients in the measurement system with measured data

from step 1.
3. Measuring a test device.

4. Computing the actual test device response with vector mathematics. [56]

42

 

Figure 4.4 Waveguide sample holder

4.6 Calibration of Network Analyzer

There are different calibration types available for transmission measurements: response
calibration, response and isolation calibration, one-path 2-port calibration, 2-port
calibration. These types differ in accuracy or in the type of errors they remove as well as
what type of measurement is required [56]. The measurement calibration process for
HP8510C VNA must be one of seven types: Response, Response & Isolation, S11 l-port,
822 l-port, One Path 2-Port, Full 2-Port, TRL 2-Port. Which process should be selected

depends on the accuracy desired and the device to be measured [56].

4.6.1 One-path 2-Port Calibration

This model provides fully corrected transmission and reﬂection measurements for a
reﬂection/transmission test set. It uses a thru, a shielded open circuit, a short circuit, and
loads to calibrate at Port 1. The operator follows instructions displayed on the CRT to

manually reverse the test device for measurement of the reverse parameter.

43

4.6.2 Full 2-port and TRL Calibrations

This model provides fully corrected transmission and reﬂection measurements with an S-
parameter test set. The Full 2-port typically used a thru, a shielded open circuit, a short
circuit, and loads to calibrate at Port 1 and Port 2. The TRL 2-port technique uses 3 thru,
short, isolation loads, and a precision transmission line. Multiple 2-port calibration is

used in the procedure for measurement of noninsertable devices.

4.6.3 Full 2-Port Calibration

Applying the standard from the calibration kit to both ports in the procedure, the response
of each standard is deﬁned and then adjusted into standard classed that correspond to the
error model in the device, in our case, used by HP8510C VNA, three known impedance
reference and a single transmission standard are required. The accuracy depends on the
accuracy of the equipment, how well the standard are modeled and the exactness of the

error correction [58].

4.6.4 TRL Calibration

TRL calibration refers to the three steps in the calibration procedure:
1) THRU: direct connection of both ports or with a short piece of transmission line.

2) REF LECT: connect identical one-port high reﬂection coefﬁcient devices to each

port.

3) LINE: insert a short length of transmission line within both ports.

44

In TRL calibration, a zero length thru used as THRU, a zero offset short, a piece of
WR340 waveguide blanking plates used as REFLECT and an existing WR340

waveguide standard section used as LINE.

4.6.5 TRL Calibration Procedure

1) THRU: set center frequency (2.2~3.0 GHz), frequency span (0.8 GHz), number of
points (201) and averaging if necessary in HP8510C VNA front panel (see Figure
4.1). Press (3) Cal. (b) WR340 — TRL. (c) TRL 2-port. (d) THRU, TRL, THRU.

2) REF LECT: Disconnect junction of WR340 waveguide straight pieces and connect
a WR340 blanking plate to each waveguide piece (See Figure 4.5). In front panel,
Press: (a) S11 Reﬂect, TRL Short. (b) S22 Reﬂect, TRL Short. (c) Isolation. (d)

Omit Isolation. (e) Isolation Done.

3) LINE: Disconnect both WR340 waveguide blanking plates and connect the
Standard section between both waveguide straight pieces. In front panel, Press: (a)

line/match, LINE 14.9. (b) Save, TRL 2-Port. (c) Select cal set.

 

Figure 4.5 WR340 standard calibration line section

4) Procedure done. Now, the system has been calibrated and ready to use.

45

5)

Calibration procedure should be done before the measurement starts. In both
calibration and measurement processes, minimizing the cable and device
movement as much as you could until all the calibration and measurement has

been completed.

4.7 S-Parameters Measurement Procedure

Samples were measured using a rectangular waveguide operating in the principal TE10

mode. Summarized measurement procedure provided to Show how to measure the S-

parameter and save to a data ﬁle on the HP8510C VNA.

1)

2)

Power on the HP8510C and perform calibration process as we described in the

measurement calibration.

Prepare the hydrated SAP specimen and place the desired specimen into the
sample holder section of WR340 waveguide (see Figure 4.4). The sample must be
homogenous and glabrous on the both surfaces. Sample thickness should be less
than 12 mm due to restriction imposed by the inversion process. Scrupulous ﬁlling
the SAP sample into the sample holder and make sure 100% fulﬁlled in the cross

section.

 

Figure 4.6 SAP specimens in the wrap

46

3)

4)

5)

6)

8)

From the VNA ﬁ‘ont panel (see Figure 4.1), Press the menu button from the
stimulus menu section. Press more from the display menu list. Select single at the

display menu list. This procedure measures four S-parameters simultaneously.

Press the disc button on the front panel of HP8510C and insert a disk into the
HP8510C, now the data ﬁle saves to a disk and is able to transfer to a computer in

which the FORTRAN Extractor installed.

Pick store from the display menu list, select memory from the display menu list.
Use the control wheel and the select letter key, input the ﬁle name.

Select the store ﬁle from the display menu.

Pull out the sample from sample holder and reload a new sample and repeat the

complete procedure until all the specimens have been measured.

Bounded Freespace Specimen Layer Bounded F reespace

\

 

 

 

 

 

\

 

Figure 4.7 Transmission and reﬂection of signals: side view of waveguide with specimen

layer

4.8 Validation of Measurements

Calibration process minimizes the systematic errors; however, measurement results have

deviation due to the imperfection of samples and other factors, such as temperature,

47

density, rough surfaces, bubbles in specimen etc. Besides calibration procedure, other
efforts have been performed to ensure the data consistency and integrity. Before testing
all samples, small trials have been conducted to ensure the temperature, density, surface,
and thickness were appropriated. Furthermore, after S-parameter measurement, loss
factor calculations performed to ensure the data integrity and consistency, Figure 6.23-
Figure 6.32 shows loss factor calculations to verify the consistency of characterization

measurement [59].

 

Fear: I-s: 29-. saw-Peers. .
:a IE. Inn .,:usnv

' V.
politic @1012

LMI.

 

   

.EIJ
.. I In :1. _ l \__ .Lm 1,5;

 

:-

Figure 4.8 FORTRAN extractor: input the initial values and extract permittivity and
permeability

4.9 Extraction Process

After measurement, a FORTRAN Extractor is used to parse the constitutive parameters
using iterative complex Newton's root-searching algorithm [48]. The ﬁle format of input
and output data is .dat that can be easily imported into spreadsheet software. A sample of

input and output data ﬁle is also included in appendix A and B.
Steps of extraction are listed below:
a. Program compilation

48

b. Initial value input
c. Acquire saved data ﬁle
(1. Computation
e. Output extracted data ﬁle.
Initial values and steps include:
1. Fraction D/A: 0.999
2. Number of modes: 1
3. Number of frequency points: 201
4. Estimated initial values: Re( a ), Im( ,u) and Re(e ), Im( a)
5. Enter input ﬁlename and path
6. Enter output ﬁlename and path.
7. Run.
That transmission/reﬂection method with Newton's iterative algorithm extracts the
complex permittivity avoids the frequency instability usually found in the process of
solving the complex constitutive parameters. The extraction process requires the
estimation of initial values for the real and imaginary parts. In many cases when the

estimated initial value does not approach the corresponding calculated values of e and ,u ,

the extraction computation would be suspended since convergence is not guaranteed. If
that is in case, iterative augment or reducing the initial values is appropriate. In the
extraction, the foregoing successful extracted values were good hints to estimate the next
initial values because the regular dielectric properties of hydrated SAP specimens
presented considerable effect of water content. It reveals that in frequency range from

2.2GHz to 3.0GHz, it is possible to have clearly estimation according to water

49

concentration in different SAP samples. The extracted constitutive parameters were

shown in Chapter 6.

50

Chapter 5
POWER MEASUREMENT AND READABILITY SURVEY

5.1 Introduction

Power is energy per unit time or energy transfer rate. For radio frequency applications,
the unit time is averaged over many periods. Average power measurement on pulsed RF
modulation Signals can be measured with power sensor [60]. The received power level of
the tag is the exclusive energy to activate the tag 1C and reﬂect digital signal to the reader.
Acquiring the power level on the transponder is the key for understanding the effect of

RF power attenuation by the SAP specimens beyond the regular path loss.

The goal of power measurement was to determine the effective power from the RFID
reader antenna after path loss and receiving power by the RFID antennas in a certain
location. The basic strategy for power measurement was to place a dipole antenna
connected to power sensor at the same location as that of the tag. Due to difference of the
impedance, area and power conversion efﬁcient, the tag antenna and dipole antenna of
power sensor receive different power levels; however, the ratio of both power reads is a
constant. Therefore, the normalized power reads of power sensor can be considered as the

power of tag received.

51

5.2 Experimental Equipment

5.2.1 Power Sensor

The R&S® NRP-Z22 power sensor is a smart standalone device that communicate with
the basic unit or a PC via a USB port. The power sensor with nominal powers of 2 W in
the frequency range from IOMHZ to 18GHz, include 90 dB dynamic range are suitable
for RFID RF signals measurement. Sensor type is 3-path diode sensor with preceding
power attenuator in stationary and periodically modulated signals. There are four
measurement ﬁinctions: continuous average, burst average, tirneslot, and scope for
recurring waveforms. (See Table 5.1) In non-recurring waveforms, there is one
measurement function: scope. Default sampling frequency is 133.358 kHz. For lower
frequency at 100 kHz to IM Hz, sampling frequency reduces to 119.467 kHz to prevent

aliasing.

 

Figure 5.1 Default data acquisition interface for power sensor

Figure 5.1 showed the default power meter interface. Power units can be shown as W,

mW, nW, dB. Measurement Resolution is MB, 0.1 dB, 0.01dB, 0.001dB, depends on the

requirements of the measurement. Power reads acquired can be logged as a data ﬁle in

PC for ﬁirther processing. The default interface for power sensor is simple and easy to

 

 

 

 

 

 

 

 

 

use.
Measurement Mode Range
Continuous Average 200 pW~200mW (-67dBm ~+23dBm)
Burst Average 200nW ~200mW (-37dBM~+23dBm
Time Slot 650pW ~200mW (-62dBm~+23dBm
Scope 10nW to +23mW (-50dBm~+23dBm
Table 5.1 Power measurement range
5.2.2 Calibration
Uncertainty

The uncertainty comes from level, temperature and frequency inﬂuences that are
impossible to eliminate in a power sensor. The speciﬁcations of uncertainty in R&S®
NRP-Z22 power sensor are based on the assumption that the measurement follows each
other so fast that the temperature of the pad does not change signiﬁcantly. S-parameter
correction and frequency response correction are the basic calibration processes to

eliminate the systematic errors.
S—parameter correction

Standard number of frequencies parameters is from 1 to 1000, for S11, S21, S12, 82;
calibration data was saved in an 52p format. When performing the calibration procedure,

the standard ﬁle should be imported into the program.

Frequency response correction

53

Carrier frequency is the center frequency (915MHz), the calibration factor is relevant for
the test frequency, 005* f (below 1 GHz) for speciﬁed measurement uncertainty,

therefore, permissible deviation from actual value 46MHz (0.05*915MHz) [61].
Average Power and Measurement time

The average power is equal to RMS value of power in the certain time slot. At the
continuous average mode, is N*(duration of measurement widow +0.2 ms) +tZ At
buffered without averaging mode, is buffer size" (duration of measurement window -0.5
ms) + tz, At burst average mode, (2 to 4)*N*burst period + t1, At timeslot and Scope mode,
is (2 to 4)* N* trigger period + II, Tz : < 1.6 ms (0.9 ms on average), if averaging is

activated, the average factor determines the number of measurement windows to be

 

 

 

 

 

 

averaged [61].
if, ‘ 7C1 D'screte PoweF
I Average power I
l C_ .,.i 2777 .
l 1.5 4
2 3 8

E 1 6

5 1 5 I

5 I
' g 0.5 . .
l e ‘
l . l
1

Tune (Seconds) 1

M, i, , , , 1

Figure 5.2 Average power measurement

54

5.2.3 2-Wire Folded Dipole Antenna
To detect the RF signal and measure the radiated power from a reader antenna at the tag
location, 2-wire folded dipole antenna which was parallel connected two half wave long

( l = %2) lines at a very small apart had been made in the laboratory (see Figure 3.1).

The length of the 2-wire folded dipole antenna was about 16.4cm equal to half of the
wavelength (915MHz), l =1/22 = c/ f =l/2*3e8/915e6=16.4cm. The antenna Gain of 2—
wire folded dipole is 1.64 or 2.15dBi. Actual gain could be a little less due to resistive

losses.

 

Figure 5.3 Two-wire folded half-wavelength dipole antenna of power sensor

5.2.4 RFID Equipment

The RFID testing equipment used for this thesis was from Alien Technology. The passive
RF ID system was operating in 902-928MH2 UHF ISM band. The transponders used in
the test were Alien Squiggle Class 1 Gen 2 tags (See Figure 5.4). The antennas were
circular or linear polarization, antenna gain is 6dBi. The antenna served as both sender
and receiver. Alien RFID Gateway v.2.12 was used in the readability survey. Two host
PCS were used in the test. One hooked-up RFID system with Intel Pentium II 300 and

Windows XP spl. The other HP Laptop hooked-up Power sensor with Window XP SP2.

55

RF ID system was connected by serial port. Reader antennas were connected with coaxial

cables.

Figure 5.4 Alien Squiggle ALL-9338 RF ID tag (Courtesy of Alien Technology)

 

5.2.5 Virtual Power Meter Conﬁguration

There are a number of ways to measure the RF power, including the use of power meter
[60]. In our approach, an R&S NRP-ZZZ standalone smart power sensor directly
connected with PC via USB port was used to measure power near the transponders
radiated from the RFID reader. The 2-wire folded dipole antenna places on the same
location with transponders. The power reads of power sensor ﬁom the antenna were
considered as normalized power of the transponders at that location. Distance, tag
orientation and reader antenna styles associated with water content were alternated to
measure and differentiate the inﬂuence of these combined conditions to power decaying
and readability within RF ID system. These measured results were compared to each of
the measurement setup; the results presented in chapter 6. A virtual control program

based on LabVIEW for the R&S NRP-ZZZ was developed. (See Figure 5.5)

56

 

Figure 5.5 Program interface of virtual power meter for R&S® NRP-Z22 power sensor

5.2.6 LabVIEW Programming

LabVIEW, graphic development platform for virtual instrument by National Instrument,
TX, USA, is the leading graphic development environment (GDE) for testing and
measurement with built-in functionality for data acquisition, instrumental control,
measurement analysis etc advanced features [62]. With the help of R&S LabVIEW
development library, many new control features and automation functions can be
developed in LabVIEW platform, which enhanced the application and convenience of
power sensor. Figure 5.6 showed the LabVIEW diagram for R&S NRP-Z22 power sensor.
In comparing with the default virtual power meter program, the customerized virtual
power meter provides automatic data saving, data conversion and instantaneous
indication and graphing. More measurement modes could be easily switched as the

measurement needed.

57

 

Figure 5.6 LabVIEW diagram of virtual power meter

5.3 Receiving Antenna Placement

In a RFID System, conductive antenna coil of a transponder is a key component to
receive the RF signal and power on the passive RFID tag. Meanwhile, it can reﬂect RF
signal from the transponders to the reader antenna [21]. The RF energy path loss,
absorption and obstructions by media between RFID reader and tags lead to reduced tag
readability. Some research suggest, using multiple antennas in a portal system enhances
the coverage and improves the readability [10]. All the steps facilitate the transponders
receiving the enough energy; however, how much energy may the tag can be received
and how much was lost in the path? The dipole antenna to power sensor measured this

parameter.

In the measurement, the 2-wire folded dipole antenna was pasted on one Side of the
hydrated SAP specimen and a reader antenna was placed on the other side. The reader
antenna was moveable. The-distance between reader antenna and tag antenna was 1cm,

5cm, 10cm, 15cm, 20cm, 25cm, 300m, 350m, 40cm, 45cm, 50cm, 550m, 60cm, and

58

65cm respectively. According to the tag orientation, rotating the receiving antenna of

power sensor was repeated and the power level was measured and recorded in data ﬁles.

5.4 Aluminum Shielding

Radio frequency signals are susceptible to shield by aluminum or other metal
obstructions. A large aluminum template obstruction (200cmx 200cm) with a rectangular
open window (17cm x 17cm) to admit the RF signal transmission was placed between the
RFID reader antenna and receiving antenna. In free space, theoretically, signal strength
and distance indicate an inverse square relation in the far-zone, which was referred in

Chapter 2.

The following graph (Figure 5.7) indicates a diagram of the components involved with
experimental setup of power and readability measurement. The Alien RFID reader
antenna (Circular and Linear) and tag antenna shown in graph were movable components

according to measurement procedures.

—+ampl¢ Window |<—
i SensortTag Antenna i

'3 P8 Board

   

 
  

       
   

  

 

% 1 1'1 T
I I at...

Roader Antenna

Figure 5.7 Experimental setup of power measurement and readability survey

59

5.5 Measurement Deviation

Calibration is necessary to achieve the accuracy of power meter, even if the power sensor
was factory calibrated. Before each measurement, a standard calibration procedure should
be performed due to the uncertainty attributed to different sources. In general, the power
meter is very sensitive and accuracy after performing standard procedure; however, the
radiated power level of reader is not stable. Graphs in Figure 5.8 to Figure 5.12 illustrated
the standard deviation of power was variance in the measurement. Measurement
experience presented reader antenna powered up time, antenna position displacement,
cables mobility, even the experimental personnel’s body in the measurement might affect
the measurement results. Figure 5.8 showed the measurement result at a typical setup.
The ﬁrst 800 reads have a relative low undulation. After that, the power reading tended to
larger deviation instead of tranquilization. Standard deviation of ﬁrst 800 reading is

0.00000019 and the standard deviation of next 400 reading is 0.00000020.

 

 

 

 

 

 

 

 

 

 

 

 

Power: 5cm, circular antenna and 40% water content
I 0.030 I— ————--—— ---- -— I
3 E .
g, 0.028 - ,_, , 41 4
i '2 0.026
l 8 W
J m 0.024
a l
I g 0.022 4---— ——~—— < 7*————4. -
< i
0.020 v 47 4 4 r4» . 4 + +——--—+——+—
1 201 401 601 801 1001 1201 '?

Figure 5.8 Periodical ﬂuctuation of discrete average power reading

60

Figure 5.9 to Figure 5.11 showed three kinds of different deviation situation in power
measurement with a vertically polarized antenna. Table 5.2 showed the mean, standard
deviation of each data group. Situation b showed a continuous decline result, the standard
deviation in that category was larger than other two situations. Thereby, in the real
measurement, though the standard calibration procedure had been performed, the
measurement was not as accurate as it should be. The strategy is to avoid the situation b,

sometimes measure the power again whenever the situation b occurs.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

O

1 2 3 4 5 6 7 8 9

Time Sequential i
L#___ __ __ ___ , l

10 11

N Minimum (dB) Maximum (dB) Mean (dB) Std. Deviation
a 10 -32.33 -32.22 -32.2690 0.03635
b 10 -15.28 -l4.87 -15.0660 0.13922
0 10 -26.53 -26.23 -26.3950 0.09733
Table 5.2 Descriptive statistics of measurement deviation
40%, 50cm, Linear, Horizontal
-31.50- ~ —-—— —
-31701
a l
E -31.90 ,
5
3 -32.101
0. i E ,
323011;] EEEEE,
|
-32504 ”44—44 4 . r . . 1

Figure 5.9 Stable average power in measurement

61

 

 

 

 

 

 

40%, 45cm, Linear, Vertical
* -14.50 4 4 4 _
-14.70'
E?
I 344.90 E i I i
a“:
$45.10 i i i {
CL I
-15.... i i
' 45.501 - . . . . . . ,
01234567891011
Time Sequencial

 

 

Figure 5.10 Continuous decline or incline deviation in power measurement

 

45%, 55cm, Circular, Horizontal

 

 

 

 

-26.00 I 444-..—
-26.20 A E E ;
3-26.401- E I i E I i E
. §-26.60I I
I Q
l -26.80E
-27.001-- . ' I . . . . .
0 1 2 3 4 5 6 7 8 9 10 11
Time Sequential

 

 

 

Figure 5.1] Undulation in power measurement

In each of Situation, a visible deviation was presented in the Figures 5.9-5.11. However,
comparison of these three situations in one graph, the line in each of Situation showed a
pretty consistency measurement (see Figure 5.12). Obvious, the accuracy is really

depending on what accuracy you need in the measurement.

62

Comparison of Power - - o - -a
- I - b y

 

 

 

 

-1o.oo 4 --t-c_)'

-15.00
-20.00 *-

 

l

f-i--)—-i——A——-A—-¢---A——A—-+

-30.oo
two-mo ---+--o---e---e---e---$
-35.oo 44— . . 1 1 .

1 2 3 4 5 6 7 8 9 10
Sequential

 

-25.00

Power (dB)

 

Figure 5.12 Comparison of measurement accuracy

5.6 Power Measurement Procedure

1) 100% ﬁll the desired hydrated SAP specimen into sample window. Other

2)

3)

4)

5)

6)

requirements are the same as in the waveguide measurement (see Chapter 4).

Place the 2-wire folded dipole antenna at the same location as the

transponders pasted.

Move the reader antenna to desired distance. Change the antenna style

according to measurement (circular and linear).

Make sure the sample window, both reader and dipole antenna are parallel

and the center of the components located in one straight line.

Open power meter program in LabVIEW.

lnput the initial values of the measurement in power meter, such as distance,

antenna style, water content, tag orientation etc.

63

 

 

 

 

 

7) Run the power meter and watch the discrete power reading graph when the

curve is stable, then start to log the measurement into a data ﬁle.

8) Change the measurement conﬁguration and repeat the measurement.

 

Figure 5.13 Hydrated SAP specimen, dipole antenna connected with power meter and
reader antenna in the other side of sample window

5.7 Readability Survey

After the power measurement procedure, removing the power meter antenna and
replacing Alien squiggle RFID tags in the same location for 100 reads using Alien RFID
Gateway (See Figure 5.13 and Figure 5.15). Recording the total successﬁll reads in a
spreadsheet. Moving the RFID Reader back and forth what is the same procedure as the
power meter measurement. The distance between RFID tag and Reader is ﬁ'om 2 cm to
67 cm in step of 5 cm respectively. Keep moving the reader antenna outward as far as the
RFID reader does not response to the tags. The results of readability were reported in

chapter 6.

64

 

Figure 5.14 Power sensor and receiving antenna in one side, mobile reader antenna in the
other side

 

Figure 5.15 Alien RF ID Gateway for readability survey

5.8 Antenna Orientation

A signiﬁcantly different performance can be attained by optimizing tag orientation in
accord with the polarization of the readers and combining dual polarized reader antennas
as a circular antenna in practical RFID implementation. The 2-wire folded dipole antenna
is a linear polarized antenna that RF energy transmits from one linear antenna to another
linear antenna is more preferable while both of antennas are co-polarized direction.

However, if the pair of linear antennas are vertical polarized to each other (90° or 270°),

65

approximate 20dB extra damping would be lost due to polarization losses. In the real
measurement, about 15dB loss was observed due to tag orientation (vertical and
horizontal), see Figure 5.16. According to Rothammel's research, only l/lOO of the
normal power could be received from the radiated electromagnetic ﬁeld [17]. However, '
combining two linear polarization antennas in form of a circular antenna which reduces
the polarization losses to 3 dB [17]. Measurement was performed in multiple
conﬁgurations among linear and circular reader antennas, tag and receiving antenna

orientations (vertical/horizontal). The results are reported in Chapter 6.

 

 

 

 

 

 

 

 

 

 

 

 

Polarization Losses ( Linear Antenna,
45%, 5cm)
0.00 44 ———~ ~
6 -5.00 -- 4
E’. _10'00..__.._!_ _I___I I I I I I I I OH
g -15.00 —44—— -- 44 — IV
‘L -20.00 4 »
O O O O O O O O O O
—25.00 -- -- 44 . T .
0 2 4 6 8 10
Time Sequential

 

 

 

Figure 5.16 Polarization losses in a linear reader antenna

66

Chapter 6

RESULTS AND DISCUSSION

The purpose of this chapter primarily deal with the experimental S-parameters, derived
permittivity from experimental result and radiated power received by power sensor near
the RFID transponders, along with tag readability using different conﬁgurations. All the
experiments in this thesis were performed on the equipment described in the proceeding
chapters. Experimental dielectric properties of saturated SAP mixtures imply that
permittivity is the critical parameter to differentiate the inﬂuence of water content in SAP
samples on RFID performance and stability. Meanwhile, effective radiated power
measured by power sensor near RF ID tags presented a straightforward inﬂuence factor
and indicated logarithm correlation on distance. Consequently, identiﬁed correlations
between water content and tag readability were created based on the afﬁliation of
permittivity, power, water content and readability using precise measurement methods

and data acquisition technique.

6.1 S-Parameters

According to transmission/reﬂection method and computation technique based on
iterative Newton's root searching arithmetic [48], ll saturated superabsorbent polymer
(SAP) mixtures with different water content, 45%, 50%, 55%, 60%, 65%, 70%, 75%,
80%, 85%, 90% and 95% respectively were measured over the frequency range of 2.2
GHz to 3.0 GHz at room temperature (68°F). The calibration and measurement procedure

were presented in the Chapter 4.

67

Figure 6.1 shows incident waves (al, a2), reﬂected waves (bl, b2) and S-parameters in a
typical two-port network. The below linear equations describes deﬁnition of S-

parameters,

b] = S1 1m + Sizaz (Equation 6.1)

b2 = Szla1+ Szzaz (Equation 6.2)

, Output reﬂection coefﬁcient S22 = 2
02:0 612

Input reﬂection coefﬁcient S11 =%

 

 

 

 

 

01:0
Forward transmission gain S 21 = —2 , Reverse transmission gain S 12 = 2I [63].
31 $21 b2
_g: A + ‘ .—
811 822
—< - 4 - 4-
b1 S12 az

Figure 6.1 The diagram of incident waves (a1, a2), reﬂected waves (bl, b2) and S-
parameters in a typical two-port network [63]

The following graphs (ﬁgures 6.2 to Figure 6.22) were created based on the experimental
result of S-parameters measurement acquired from HP8510C VNA. The thicknesses of
hydrated SAP specimens (see Figure 4.4) were 12mm and 7mm in two independent trials.
In most graphs, S-parameters showed a small ﬂuctuation with frequency increasing.

water content in high frequency has larger inﬂuence to S-parameters.

1. Input reﬂection Coefﬁcient:

68

The real part of 811 increases with the frequency increasing, on the contrary, the
imaginary part of 81] decreases. Higher water concentration in thinner samples

(7mm) shows faster increasing in real part of S] l,
2. Output reﬂection coefﬁcient

Both real part and imaginary part increase with frequency increasing, water content

is a major inﬂuence, higher water concentration, faster increasing.

For ideally lossless dielectric substance, the magnitude of $11 (=2 ) and
la2=0
$22 (= b—: )are equal [63]. However. they can deviate from one another whenever
(11:0

loss is presented.

Figure 6.2 showed that input reﬂection coefﬁcient (81 l) in hydrated SAP mixture with
70% water content has a linear relationship with frequency. However, in homogenous
samples, the thickness is another major inﬂuence to SI 1. The slope of 7mm sample was
larger than that of 12mm sample. Consequently, the deviation may be occurred in
different trials due to sample thickness, density etc. Figure 6.3 showed that output
reﬂection coefﬁcient (822) at SAP mixtures with 55% water content has a linear
relationship with frequency. However, the same reason as we mentioned, in homogenous
samples, sample preparation as such thickness is major inﬂuence to $22. The slope at 7
mm SAP sample was larger than that of 12mm sample. In the ideally substance,
81 i=822. However, the hydrated SAP mixtures in the experiments presented a lossy

characteristics. 81 1 showed the linear relation over the frequency range, in different trials

69

with same water content, 7mm sample had a larger slope and 12 mm sample had a larger

slope in the graph. 822 showed the same property as S] l.

12
S11 vs. Frequency at SAP (70%) : m? I
I - - - Linear (7mm) I
_0 70 ___ _ _ I_ - - —Linear (12mm) .'
-075 - y(12) = 0.0742x - 1.0428
2_ , ’
-080 R -O.8551 “4." I I
"' :1." —O- *‘O’ ‘9'— I
5 ~0.85 _'_._,__ .1.”
~ -090 " t _ .. y(7)= 0. 2095x- 1 3952
I a
3 -095 "' R2 = 0.9939
-1.00 I- I
2.20 2.40 2.60 2.80 3.00
Frequency (GHz)

 

 

_,

 

 

 

 

 

 

 

 

Figure 6.2Comparison of 811 in SAP specimen with 70% water content

822 vs. Frequency at SAP (55%) I . 12mm
I I 7mm
0.40 4
0.20 I y(7)=12.-2428x 3.4798 ."’I
0.00 I R2 =0.9965 "VII" |
I a -O.20 -. I',I’. O . 1. .v-tb
‘ -0.60 I41 :. .w ° " y(12)= 0.6925x 2.2818
~0-80 I” R2 =0.9925
-100 444 4 - 4 __4 .4 - 4 I
2.20 2.40 2.60 2.80 3.00
Frequency(GHz)

 

 

 

 

 

 

 

 

 

Figure 6.3 Comparison of 822 in SAP specimen with 55% water content

70

 

I 9 12mm
821 vs. Frequency at SAP (80%) I 7mm
-— — Linear (12mm)
0.20 _ ---- Linear (7mm)

 

 

 

0.00 It“ I +,_.,
|

+' .___. 4.44%, +‘ﬁ‘4’

R2 = 0.971

821

 

 

I -0.20 I y (12)= 0.1361x - 0.3721

-0.40 I

I y (7): 0.2197x - 1.4264

-0.60 I R2 = 0.9968
I -0.80 . _ ...I-I-l"'-
I l-I-I--I-I-l-l""" '
1 -1.00 . . .

2.20 2.40 2.60 2.80 3.00

 

Frequency (GHz)

 

Figure 6.4 Comparison of $21 in SAP specimen with 80% water content

Figure 6.4 showed that forward transmission gain 821 over frequency in two trials with
same water content and different thickness. The thicker sample had small slope that
indicted it was more sensitive to frequency in thinner sample with the high water content.
In Figure 6.5, reverse transmission gain, 812 showed relative complex relationship over
frequency. 812 at 12mm sample slowly increases with frequency increasing, however,

S 12 at 12mm sample gained a quickly decline over frequency.

Because permittivity and permeability were extracted from the experimental S-
parameters, we discussed the S-parameters only limited on the data integrity and
validation purpose. Figure 6.6 to Figure 6.21 showed the comparison of S-parameters in

all measured SAP samples with different water content.

7]

 

 

 

 

 

 

 

812 vs. Frequency at SAP with 60% water content
0.00
y(12) = 0.1917x2 - 09227:: + 1.0268 , 4' 'I
-0.04 I‘ . 2 oz.
f I . R = 0.9785 )_ ,e— '
I . . ...v.‘
9.. '0-08 %.."0° I’v‘T.-.. ‘.' -O" 0 12mm I
a) 1 . ~ . 7 I
-012 - '4‘ _"‘"‘ J1
... 1-
-0.16 I y(7) = 0.2371x2 -1.3945x + 1.887 " " I - I - I - I -I
I R2 = 0.998
-0.20 - .
2.20 2.40 2.60 2.80 3.00
Frequency (GHz)

 

 

Figure 6.5 Comparison of S12 in SAP specimen with 60% water content

 

S11(real) in SAP Samples (12mm)

 

- -A - 55%
+60%
+ 65%
4 a — 70%
- - + - - 75%
—e—80%
. — -e- 85%
-1.00 . ~~ I — I 4' —-o—90%

2.20 2.40 2.60 2.80 3.00 —Cl—95%

I Frequency (GHz)

S11(real)

 

 

 

 

 

 

 

 

 

Figure 6.6 Comparison of experimental Sll (real) in SAP mixtures (12 mm)

72

 

 

 

      

 

 

 

 

S11(rea|) in SAP Samples (7mm)

-0.60
— -A - 55%
-0-70 +60%
g + 65%
5 -0.80 — a — 70%
5 - - +- - 75%
-0.90 —0— 80%
' I — -e- 85%
-1 .00 J ‘ i _._ 90%
2.20 2.40 2.60 2.80 3.00 _g_ 95%

Frequency (GHz)

 

 

Figure 6.7 Comparison of experimental 811 (real) in SAP mixtures (7 mm)

 

 

 

 

 

 

 

 

1 S11 (img) in SAP Samples (12mm)
I 0.50 44 4— -. *
I o 40 .. - ' A- - - 55%
0.30 I —-x—60%
is; 0.20 ’ + 65%
E 0.10 — * - 70%
‘73 0'00 ' ---+--75%
‘ -010 —°— 80%
-0-20 . I , - -°- - 85%
2.20 2.40 2.60 2.80 3.00 + 90%
—°— 95%
Frequency (GHz) ___—

 

 

Figure 6.8 Comparison of experimental Sll (img) in SAP mixtures (12 mm)

73

 

S11 (img) in SAP Samples (7mm)

 

 

0.50
0.40
0.30
0.20
0.10
0.00
-0.10

-0.20
2.20

S11(img)

 

 

- ~A — 55%
—x— 60%
~-—X—- 65%
*—— t — 70%
- - + - - 75%
+ 80%
- -e— 85%
+ 90%
—D— 95%

 

 

2.60 3.00

2.80

2.40

 

 

Frequency (GHz)

 

Figure 6.9 Comparison of experimental Sll (img) in SAP mixtures (7 mm)

 

  

822 (real) in SAP Samples (12mm)

 

 

 

 

 

 

0.30 __ _A _ 55%
I 0.10 +60%
i 5, -0.30 — * — 70%
8‘: -050 --+--75%
-070 +30?
-0.90 * 4 85 /0
+90%

2.20 2.40 2.60 2.80 3.00
+95%

Frequency (GHz)

Figure 6.10 Comparison of experimental 822 (real) in SAP mixtures (12 mm)

 

 

 

 

74

 

822(real) in SAP samples (7mm)

 

 

 

 

 

 

0.30

0 10 - - av- 55%

I ' + 60%

l :3? '0-10 a4 65%

‘Q’ -0.30 ‘_ f _ 70%

<0 -0.50 ---+---75%

-0.70 + 80%

I -0 90 I - "0" ' 85%
l ' O

l 2.20 2.40 2.60 2.80 3.00 ° 90"

—0-— 95%

 

 

 

Frequency (GHz)

 

 

Figure 6.1 1 Comparison of experimental 822 (real) in SAP mixtures (7 mm)

 

 

 

 

 

 

 

 

 

 

822 (img) in SAP Samples (12mm)
1.00

0.90 - -A - 55%
030 +60%
’2" 0.70 + 65%

C _ _ 0
a 0.60 * 7° /°
to - - + - - 75%
0.50 . 80%
0-40 - -e— 85%
0.30 . 1 +90%
2.20 2.40 2.60 2.80 3.00 —a— 95%

Frequency (GHz)

 

 

 

 

Figure 6.12 Comparison of experimental 822 (img) in SAP mixtures (12 mm)

75

822(Img)

812(real)

Figure 6.14 Comparison of experimental 812 (real) in SAP mixtures (12 mm)

 

$22 (img) in SAP Samples (7mm)

 

 

1.00
0.90
0.80
0.70
0.60
0.50 .
0.40 r
0.30 L-v'

 

 

 

 

2.40 2.60 2.80
Frequency (GHz)

3.00

——x——60%
~—+65%
~— t — 70%
---+---75%
+80%
--o-— 85%

—-9—90%

 

 

--—o— 95%

 

 

 

 

l

2.40 2.60 2.80

Frequency (GHz)

76

— -A - 55%

+60%
+65%
»— t — 70%
--+-- 75%
+80%
--e--85%
+90%
+95%

 

 

 

 

 

 

S12(real) in SAP samples (7mm)

 

 

 

I— -A - 55%
I—x— 60%
l + 65%
--—— t —— 70%
- - + - - 75%
—0— 80%
— -e— 65%
* —+— 90%
2.20 2.40 2.60 2.80 3.00 —-n— 95%
Frequency (GHz)

812(real)

 

 

 

 

 

 

 

Figure 6.15 Comparison of experimental 812 (real) in SAP mixtures (7 mm)

 

S12 (img) in SAP Samples (12mm)

 

0.50 {-4 4 44
0.40 ‘

0.30
0.20
0.10
0.00
-010

-0.20
-030 _. 4 -—4- 4 1 J +90%

2.20 2.40 2.60 2.80 3.00 +95%
Frequency (GHz)

 

S12(img)

 

 

 

 

 

 

 

Figure 6.16 Comparison of experimental 812 (img) in SAP mixtures (12 mm)

77

 

S12 (img) in SAP Samples (7mm)

 

 

 

 

— ~A- 55%
+60%
+ 65%
-— 1k — 70%
- - + - - 75%
+80%
- -e- -85%
—+——90%
2.20 2.40 2.60 2.80 3.00 +95%

Frequency (GHz)

S12(img)

 

 

 

 

 

 

 

Figure 6.17 Comparison of experimental 812 (img) in SAP mixtures (7 mm)

 

 

 

 

 

 

 

821 (real) in SAP Samples (12mm)
0.20

--A- 55%
0.10 —)(—60%
‘§0.00.-. ”$659"
I f: ' ' —t—70%
. a '0-10 --+--75%
, -020 +80%
_ _. 0
.030 L 4 . . ° 85"
+90%

2.20 2.40 2.60 2.80 3.00
+95%

Frequency (GHz)

 

 

Figure 6.18 Comparison of experimental 821 (real) in SAP mixtures (12 mm)

78

821 (real)

 

 

 

821(real) in SAP Samples (7mm)

 

, l—-A-55%
! +60%
' +65%
4t—~70%
--+--75%
+80%
--O--85%

 

--O— 90%
—O— 95%

 

2.40 2.60 2.80 3.00
Frequency (GHz)

 

 

 

._-.____ .—

Figure 6.19 Comparison of experimental 821 (real) in SAP mixtures (7 mm)

821(img)

 

$21 (img) in SAP Samples (12mm)

 

 

 

- -A - 55%
+60%
——x— 65%
4 i — 70%
- - + - - 75%
—0-— 80%
— -e- -85%
— . ' +90%
2.40 2.60 2.80 3.00 +95%
Frequency (GHz)

___ L _

 

 

 

 

 

 

 

Figure 6.20 Comparison of experimental 821 (img) in SAP mixtures (12 mm)

79

 

$21 (img) in SAP Samples (7mm)

 

 

- -A - 55%
+60%
—x—— 65%
--— t — 70%
- - + - - 75%
—o—80%
- -e— 85%
1 ‘ +90%
2.20 2.40 2.60 2.80 3.00 +95%

Frequency (GHz)

$21(img)

 

 

 

 

 

 

 

 

Figure 6.2] Comparison of experimental $21 (img) in SAP mixtures (7 mm)

6.2 Validation

Calibration procedure eliminates the systematic errors. However, ideally homogenous
status is far to reached, the imperfect samples causes deviations in measurement.
Validating measurement ensures data integrity. In the material characterization
measurement, two independent experiments were performed to validate the consistency
of measurements. In two independent trials, the sample thickness was 12 mm, 7 mm
respectively. Loss factor is a constant that reveals the power damping in a network.
However, loss factor calculations shown the measurement quality are able to validate
passive S-parameter measurements [59]. The forward loss factor (F LF) and reverse loss

factor are determined by S-parameters as follow equations:

2 2
Forward Loss Factor: FLF =1—|S11| — |S21| (Equation 6.3)

80

2 2
Reverse Loss Factor: RLF = 1- IS 22I — IS 12' (Equation 6.4)

Figure 6.22 to Figure 6.30 was based on the calculations and presented the validation

results with loss factor calculations. It showed data inconsistency in FLF with 80% water

content, nonetheless, in all other graphs, it showed pretty good data consistency. We

discarded the deviated parameters of SAP with 80% water content in later discuss.

 

 

 

 

 

 

 

 

Loss Factor vs. Frequency in SAP (55%)
2.00 ~—-—-————-——— I
r l .
.. 150
8 OFLF_12mm ‘
63100 ooonoooooanaonn UHF-7mm
g ' ‘ ‘ ARFL_12mm
o x A A A . XRLF_7mm I:
"'050I Xxx “‘ALA“ ___I
I x X X x x x x x x x Q
0.00 ——— __-_ ~ ~ .
2.20 2.40 2.60 2.80 3.00

Frequency (GHz)

 

 

 

 

Figure 6.22 Comparison of loss factors in SAP samples (55%)

Loss Factor vs. Frequency in SAP (60%)

 

 

 

 

 

 

 

 

 

2.00 44- -4 ~ 4
g 1'50 l L OFLF_12mm
«5 i DRLF_12mm
t 100 I ﬁﬁﬁﬁﬁﬁﬁﬁﬁaa XFLF_7mm
:3. 0 50 _ an ﬁﬁ XRLF_7mm
0.00 4 4 4 .
2.20 2.40 2.60 2.80 3.00 I
Frequency I
V, 7 , S--- , , _ _h -.-4

81

Figure 6.23 Comparison of loss factors in SAP samples (60%)

 

Loss Factor vs. Frequency in SAP (65%)

 

 

 

 

 

 

2.00 4 4 44444 4
h 1.50
,3 OFLF_12mm
m DRLF_12mm
“J, 1'00 H 5 3 5 AFLF_7mm
8 E E XRLF_7mm
-‘ 0.50 . 5

 

.40 2.60 2.80 3.00
Frequency (GHz)

 

 

 

Figure 6.24 Comparison of loss factors in SAP samples (65%)

 

 

 

 

Loss Factor vs. Frequency in SAP (70%)
2.00 I 4 —— 4 ——
I
.. 1.50 I» I
,3 . OFLF_12mm—I
m ’ DRLF_12mm
E1OOI xxxééééﬁaaﬁ XFLF_7mm
3 I X E] D D D XFLF_7mm .
0 50 6 5 0 ___"
gagggggguut¥¥33§
0.00 1 1 I
2.20 2.40 2.60 2.80 3.00

I
I
Frequecny (GHz) I

 

Figure 6.25 Comparison of loss factors in SAP samples (70%)

82

 

Loss Factor vs. Frequency in SAP (75%) I

 

 

 

 

 

 

2.00 I" —- a— . 4_r,
I
g 1.50 I OFLF_12mm
m DRLF_12mm
310°? xxxxséééam
8 X x El 0 D U XRLF_7mm
—1 0.50 E D U
ganglion-06666666
000 . I 1
2.20 2.40 2.60 2.80 3.00
Frequency (GHz)

 

 

 

Figure 6.26 Comparison of loss factors in SAP samples (75%)

 

Loss Factor vs. Frequency in SAP (80%)

 

 

 
 
 
 

 

 

 

2.00 — 4 I
I
1.50 I I
5 _.____I
H 1 00 l
o xxxxx¥¥¥¥¥ 0FLF_12mm
ILiSOSO x¥§§§+++++ +RLF_12mm
a $<><><><><><><><><>o<><><><> AFLFJmm
o 0.00 XRLF_7mm
_J A A
0.50 I A A A A A A I
I -1.00 L _x . .
2.20 2.40 2.60 2.80 3.00
Frequency (GHz)

 

 

Figure 6.27 Comparison of loss factors in SAP samples (80%)

83

 

 

Loss Factor vs. Frequency in SAP (85%)

2.00 —44444—44
31.50}
*- I
O I
m .
1.1.100;
w j xxxxxgéﬁﬁﬁﬁl
8 I xx 13000
40.501-X D

0.00

D
g::....s355555§§

 

 

 

o FLF_12mm
El RLF_12mm
X F LF_7mm
x RLF_7mm

 

 

2.20

2.40 2.60 2.80 3.00
Frequency (GHz)

 

Figure 6.28 Comparison of loss factors in SAP samples (85%)

 

Loss Factor vs Frequency in SAP (90%)

2.00 -

1.50 I

1.00 r

Loss Factor

0.00
2.20

0.50 x

 

 

 

2.40 2.60 2.80 3.00
Frequency (GHz)

 

 

o FLF_12mm
D RLF_12mm
A FLF_7mm
x RLF_7mm

 

 

Figure 6.29 Comparison of loss factors in SAP samples (90%)

84

 

 

 

 

 

 

   
   

 

 

Loss Factor vs. Frequency in SAP (95%)
2.00 4— —4——~
I .
5- 1.50 - 4~——-—
I g, I =0FLF_12mm I
I m I DRLF 12mml
| u. -
ImmoI xxxxgﬁﬁﬂ"'”' AFLF_7mmI
8 Ixxxnnnn xFLF_7mm I'
.1050 Dan “““AA
ggge668oooooooo I
0.00
2.20 2.40 2.60 2.80 3.00

Frequency (GHz)

Figure 6.30 Comparison of loss factors in SAP samples (95%)

6.3 Permittivity

Measurement and extraction procedures of material characterization using HP 8510C
vector network analyzer with WR340 waveguide were described in Chapter 3 and
Chapter 4. The results of the permittivity in term of dielectric constant and loss factor
based on the experimental measurement. With a dielectric constant of near 80, water
dominates main component of hydrated superabsorbent mixtures due to high
concentration of water in the experiment. However, there does not appear to be one
widely accepted model for estimation of dielectric constant in water-saturated SAP
mixtures. Figure 6.3] showed experimental permittivity and permeability in SAP sample
with 5% water content. The graph indicated deviations of experimental permittivity. It
showed the thicker sample (12 mm) has a higher permittivity. Obviously, it is not true

theoretically. The deviation came from the wave propagation in waveguide. Though the

85

deviation indicated ﬂuctuation in measurement, the permittivity had good match over the

ﬁ'equency range.

 

 

 

 

 

 

EPR & MUR vs. Frequency in SAP (55%)
30 - 0Re{EPR}-7mm
++++ +++ ++ +
20 _<>_<>_Qo_o_Q<L:$-_Qo_§Q$$ DIm{EPR}-7mm
‘5 1o _ ___ 4 4 4 4 4 4 esRe{MUR}-7mm
2
5‘5 0 HHHHHHH! x|m{MUR}-7mm
a. -10 __ 4 _ 4 __ __ _
u +R EPR 12
“-20 DLQREQE 153395”; °{ * mm
7 -lm{EPR}-12mm
I _30 l 1 . J 4 L 4
I 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9 3.0 *RelMURWm'“
Frequency (GHz) 0 lm{MUR}-12mm

 

 

 

 

Figure 6.3] Comparison of experimental permittivity (EPR) and permeability (MUR)

Figure 6.32 to Figure 6.35 were created based on extracted permittivity from S-
parameters, which showed the real part of permittivity in SAP mixtures with different
water content over frequency range 2.2~3.0 GHz. They indicated that dielectric
permittivity is fairly stable over ﬁ'equency range 2.2 GHz to 3.0GHz. However, water
content in SAP mixtures is the major inﬂuence on ﬂuctuation of permittivity. General,
high water content in SAP mixture gained high permittivity. the correlation of relative

permittivity and water content was presented in Figure 6.36.

Figure 6.32 and Figure 6.33 showed the real part of relative permittivity (dielectric
constant) is relatively stable over the frequency range, it showed a slightly decreasing
tendency for thinner samples and relatively low water concentration samples (55%, 60%,

7mm). The permittivity of the rest of samples shows relative invariability or very slight

86

increase over part of the frequency range. Meanwhile, it showed SAP mixtures with
lower water concentration has lower relative permittivity (dielectric constant), the
correlation and graphs shows in Figure 6.36 and Figure 6.37. However, Figure 6.34 and
Figure 6.35 showed a relative larger ﬂuctuation of permittivity, SAP sample with 95%
and 12 mm thickness showed an unexpected result, with so high water content (95%), the
permittivity declined quickly over the frequency range, in comparing with the thinner
sample but with same amount of water. the unexpected result might be caused by the
imperfect of sample. In frequency range 2.6GHz to 2.7GHz, the permittivity of 95% SAP
mixture reached near 80 which is almost permittivity of pure water. Generally, the
relative permittivity of the saturated SAP mixtures was in the range of 10 to 80. The
dielectric constant of pure water is about 80. It showed that the dielectric constant of the
SAP mixtures relied on the proportion of two components. With the water content
increasing, the dielectric constant of the SAP mixture proportionally increased (see

Figure 6.36 and Figure 6.37).

87

 

Comparison of Permittivity (real/F) in SAP ( 12 mm)

 

 

 

 

 

70.00
a 60.00‘ a l
(U
2 I
.«E‘
.2
3:5 .
E
a; 20.00 HH—X—X—H
‘L 10.00
0.00 L
2.20 2.40 2.60 2.80 3.00
Frequency (Gl-lz)

 

 

--A-~55%
—x—-60%
+ 65%
A— — 70%
----+ 75%
—-o-—80%
--o-- 85%
—o-—90%
+95%

 

 

20.00
10.00
0.00

Permittivity (real)

2.20

 

,or
- -°~o--e-o--e-o-o~o--e-o--°

ﬂit _ Iliﬁinl ‘

 

 

2.40 2.60

Frequency (GHz)

2.80

 

--A---55% '
+60%
----—-—)1(4 65%
4 A— —70%
-~---+- 75%
—e—80%
--o--85%
+90%

 

+95%

 

 

Figure 6.33 Comparison of permittivity in SAP with different water content (7 mm)

88

 

 

 

 

 

Comparison of Permittivity (real/R) in SAP (12 mm)

 

 

Permittivity (real)

 

 

 

2.20 2.40 2.60
Frequency (GHz)

2.80

 

 

- -A — 55%
+60%
+65%
—- t- — 70%
- - + - -75%
+80%
— -e— 85%
+90%
+95%

 

 

 

Figure 6.34 Comparison of permittivity in SAP with different water content (12 mm)

Figure 6.36 to Figure 6.38 were created from experimental relative permittivity and
standard deviation among 201 points in the range of 2.2 GHz to 3.0 GHz. It was overt
that in this range, the permittivity was very sensitive to water content. they presented that

the relationship between the relative permittivity and the water content was ﬁt for linear

regression from 45% to 95% in SAP mixtures.

Comparison of Permittivity (real/R) in SAP (7mm)

85.00

 

75.00
65.00
55.00
; 45.00
35.00
25.00 .
15.00

5.00

My (real)

Perrnrtt

 

 

I 2.20 2.40 2.60
Frequency (GHz)

2.80

3.00

 

 

- -A - 55%
+60%
+65%
~ t —70%
- - + - -75%
—O—80%
- -G- 85%
+90%

—0— 95%

 

 

 

Figure 6.35 Comparison of permittivity in SAP with different water content (7 mm)

89

 

_._._J

 

 

 

 

 

 

 

 

 

 

Relative Pennittvity vs. Water Concentration
80 ,
7o . R2=0.8627
: A .
’5’ 60 , ,a’
g 50 ‘ '9' ’ ’ I
E ’ a A: I ’
g 40 R2 = 0.8543 r; , {Cl-:13
@ . ’ 0’ I i E
1?. 3° T D , E / E A 7mm ‘
(or; 20 i , '5, - D i [:1 12mm I
’,-’ £3 '—--Linear(7mm)
10 ‘ l |
l— — Linear (12mm) l
0 i _.___1__ l J i
45 55 65water 9 i 75 85 95

 

 

Figure 6.36 Correlation of relative permittivity in different sample thickness

Dependence of the experimental relative permittivity, under RT 68°F at 2.ZGHz to
3.0GHz, the permittivity is proportional to the water content in the SAP samples. Two
distinct experiments were observed. The result of bivariate correlation analysis showed
these variables were highly related to a linear relationship because Pearson's correlation
coefficient of water concentration and permittivity were 0.869, 0.932 and 0.966

respectively with their signiﬁcance levels. (See Table 6.1)

 

 

 

 

WATER 2mm 7mm

Pearson Correlation 1 .869 .932

WATER Sig. (2-tailed) . .002 .000
N 9 9 9

Pearson Correlation .869 l .966

12mm Sig. (2-tailed) .002 . .000
N 9 9 9
Pearson Correlation .932 .966 1
7mm Sig. (2-tailed) .000 .000 .
N 9 9 9

 

 

 

 

 

 

 

"Correlation is signiﬁcant at the 0.0] level (2-tailed).

Table 6.1 Correlations of water concentration and sample relative permittivity

90

Figure 6.37 showed at 2.4SGhz, 12mm and 7mm SAP samples presented a pair of
contiguous permittivity curves which were almost superposition with each other.
However, loss factor (imaginary part) showed larger deviation in comparing with real
part. Figure 6.38 indicated that there were larger deviations in 7 mm SAP samples than
12 mm SAP samples. However, It presented that water content was major inﬂuence to
deviation, higher water content came higher deviation. However, the sample with higher

water content usually has a higher permittivity.

 

 

 

 

 

 

 

 

 

EPR vs. Water Content at 2.4SGHz
'_ 0 Re{E}-12 ‘
80.00 T . x MEN
60.00 t x Re{E}-7
40.00 ~
0: A lm{E}-7
a. 20.00 F
”J Poly.
0.00 . , . ' ' . (Re{E}-12)
X . 11; ;---Poly.
-2000 4.31.. u.;_..__._§;-_*-‘-,§.- E g ..... £2337)
-40.00 . . ‘4 . A - . . .. (|m{E)-12)
55% 50% 55% 70% 75% 50% 35% 90% 95% - - - 4:00.
{ wt% water content l ("HE”)
E _,v,,___ ___

 

Figure 6.37 Permittivity vs. water concentration at 2.45GHz in different sample
thickness

91

 

 

 

 

 

 

 

Sthev vs.Water wt%
5.00 r-——-- - ~-- - —
T T- O- - 7mm El
4 00 L T- i - 12mm 1 .
T ' i i— — — Poly. (7mm) 1 j,
I . g— I“ - Poly. (12mm)' .f
> 3.00 >— W ,q, / ’-
. 8 ' \ ’3. -- d A
; : I ‘ I. /
. P- 200 1 ' \ ”’9’ . , ’
T ‘0 l ’ ‘ ’ ’ ' ’ ’
- I § ' _’ ,— 4: H ‘5' ‘- '5
. ______ f— /' .\’ . 7,4”
1.00 G- .i . J’ g ‘ *3
T -r’A‘: ' .— -<‘A/
0.00 J_§-1 l 1 i l l l l 1 1 i
45 55 65 75 85 95
wt % water content

_- J

Figure 6.38 Standard deviation of relative permittivity in different sample thickness

 

 

 

 

   
 

 

 

 

 
 
  

 

 

 

1 Monte Carlo Similation-100% water
T
‘ 68.00 1 2
67 00 y(7) = 4.0646x - 28.725x + 111.02
1 ' } 2
T 66.00 R = 0.9375 _ _. _ 7mm
‘ £3 65.00 1 ‘ ' "" ‘ 12"“ =
; .35 - - - - Poly. (12mm) 1
T E 64'00 T Poly. (7mm)
: g 63.00 ~- \ x)‘
T 6100 T y(12) = 5.0246x2-33.51x 16.66
61"” T R2 =0.9432
60.00 T 1 ‘ 1
1 2.20 2.40 2.60 2.80 3.00
T Frequency (GHz)

 

 

Figure 6.39 Estimated permittivity of 100% water

Figure 6.39 showed a group of estimated permittivity of 100% water using Monte Carlo

Simulation. Obvious, the real permittivity value over the frequency range was smaller

92

than the value in literature. It was hypothesized that the Monte Carlo Simulation soﬂware
used the right experimental permittivity. However, in the SAP mixtures, part of water
molecules were associated with SAP molecules forming part of bounding water. As the
water concentration increases, the strength and extent of the hydrogen bonding both
increase. This leads to the experimental value lower than theoretical values.
Consequently, estimated value was lower than that of 100% pure water in literature.

Furthermore, bounding water in SAP would cause a higher loss factor theoretically.

6.4 Loss Factor

The imaginary part of permittivity referred as loss factor in this thesis presented the lossy
character of the substance. The loss factor of the SAP specimens slowly increased with
increasing frequency at room temperature. Figure 6.40 to Figure 6.41 based on the
measurement showed that water content was major inﬂuence affecting loss tangent.
Lower water content corresponded to a lower loss tangent while higher water content
resulted in a higher loss tangent. Loss factor increases slowly and placidly; however, in
Figure 6.40, there was different trend in SAP sample with 95 % water. Figure 6.4]
showed that loss factor of 7 mm SAP samples was turbulent over the range in comparison
with Figure 6.40. Figure 6.43 showed the standard deviations in thinner samples (7mm)

were larger than those of in thicker samples (12mm).

As the water concentration increases, the strength and extent of the hydrogen bonding
both increase. This elevates the static dielectric permittivity, enhances the difﬁculty for
the movement dipole and so prevents the water molecule to oscillate at higher

frequencies and boost up the drag to the rotation of the water molecules, so increasing the

93

 

friction and hence the dielectric loss factor increases. Experimental dielectric loss factor
of saturated SAP mixtures with 55% to 95% water showed major inﬂuence of water
content which caused ﬂuctuation of loss factor; however, it did not show simple

correlation or linear relationship. The mechanism of loss factor is complicated.

Comparison of Loss Factor in SAP (12 mm)

 

 

- -A - 55%
+60%
—— +— 65%
— + — 70%
- -* - 75%
—O—80%
- -e- 85%
—0—90%
2.20 2.40 2.60 2.80 3.00 +95%

1 Frequency (GHz)

Loss Factor

 

 

 

 

 

 

 

Figure 6.40 Comparison of loss factor in SAP with different water content (12 mm)

 

 

 

 

  

 

 

 

Comparison of Loss Factor in SAP (7 mm)
1
T
; 0.00
— ~A — 55%
b -10.00 +60%
0
1% +65%
I; -20.00 _ t —70%
; g - + - 75%
T -30.00 + 80%
- -e- 85%
-40.00 ‘ J —o— 90%
2.20 2.40 2.60 2.80 3.00 T_g_ 95%
Frequency (GHz) '

 

 

Figure 6.4] Comparison of loss factor in SAP with different water content (7 mm)

94

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Comparison of Loss Factor in SAP
20.00
|—' _' ——|
10.00 . I—°~7mm { A
.5 0.00 1 T_-¢-12_,m_'ﬂg ,'
8 5.. .'
I; -1000 — 'A. f. a ,5 a
m “RH-A- / p ‘\ 'K. D
3 -20.00 - 6‘5 » ‘A~.A/' a
-30.00
a
-40.00
45 50 55 60 65 70 75 80 85 90 95
Waterwt%
Figure 6.42 Loss factor of different samples
Sthev vs. Wt%
6.00
500 - T—o-7mm T /Q o
400 F TL: *M " \'. I,
g: ' d \‘ [.4
.g 3.00 » o. / omit—no"
a) / \ ,' .o
D 2.00 “d
d "5 ‘ﬁ-o A A. A
1.00 L ,4" 1
A" }
0.00 . . . . . . . + . .
45 50 55 60 65 70 75 80 85 90 95

Water (wt%) 1
u _ _ __ _______1

 

Figure 6.43 Standard deviation of loss factor in different thickness

6.5 Loss Tangent

Figure 6.44 to Figure 6.48 were created based on the measurement. Figure 6.44 and

Figure 6.45 showed the loss tangent in 12mm and 7mm SAP samples. The loss tangent

95

referred to ratio of dielectric loss factor (52 ) to dielectric permittivity (£1 ),

tan 5 = 82 / 81. It presented that loss tangent converged while frequency went to high
frequency in 12mm SAP samples. However, in 7mm samples , larger undulation of loss
tangent occurred over the tested frequency range. Nonetheless, high water content

presented larger loss tangent in SAP samples.

 

 

   

 

 

 

Loss Tangent in SAP (12mm)

"€759:

1.40 x x‘n x ...,_50%
x”'**** H“ -—.—55%

E 0.90 , o
g .4»:— - — x 60/o
c ’— 5 o/

1 .9 040 _7___- _ ——-x-—'6So
3 ‘W‘ . 70%
3 010 (hr. T -—+ ~75%

. '“' . _ - —80%

1 -0.60 T L - 1 J _._-__35%
‘ 2.20 2.40 2.60 2.80 3.00 l_. __90%
Frequency in.- _95%
L___ ___

 

Figure 6.44 Loss tangent in 12 mm SAP samples

96

 

 

Loss Tangent

 

 

 

 

 

 

 

 

 

 

 

1.00
‘E 0.80
o
2’ 0 60
1 1‘3 '
T a 0.40
T 3
' 0.20
0.00 _, - o
2.20 2.40 2.60 2.80 3.00 +95%
frequency (GHz)
Figure 6.45 Loss tangent in 7 mm SAP samples
Loss Tangent T . 2.456112 ___ﬁ
j A average
1.00 , —— " T ..... Linear (2.456Hz) ‘
‘ O
.. 0.80 7 A TTT.‘ -Linear (average)
5:.) ‘ TTTT x l
2’ 0.60 1 ~~~~~
<0 ‘0—\
P ‘~~‘
g 0.40 T ‘ . ~‘\“\t .
3 T ‘ “‘-~ 1
0.20 1 ‘ “ r
‘ 1
000 T _ 1 # _1.__ _ 1 1 1 1 T

 

 

 

 

 

Figure 6.46 Comparison of loss tangent at 2.45 GHz in 7 mm samples

97

 

 

 

Loss Tangent

 

 

 

 

 

 

2.50 —# .—#___T- 1‘ A- - 12mm _ﬁ
' 0 I-—-—D —7mm

*-' 2'00 5 ' Poly. (7mm)

c .

g, 1-50 f _ it ------ Poly. (12mm);

.52. 1.00 ‘

3

o 0.50

A l
0.00 .
-0.50

 

 

 

 

 

Figure 6.47 Comparison of average loss tangent in SAP samples

Figure 6.46 to Figure 6.48 presented comparison of loss tangent with various conditions.
In Figure 6.46, the loss tangent in 2.45 GHz was really agreed the average loss tangent in
SAP samples, loss tangent declines with the water content increasing. Average loss
tangent in 7mm and 12 mm were matched pretty well. Figure 6.48 presented that loss
tangent in 12mm SAP were stable, however, both of loss tangent in SAP with 65% water

content showed a linear correlation over the frequency range.

98

 

 

 

 

 

‘ . l A 12mm
T Comparison of Loss tangent 1 a 7mm
' ----- Linear (12mm)

T 3.50 ;_ ____ ___-___. _. _ _____ ___.1 — — - Linear (7mm)

1 T 7 = 1. 74 - 1.

1 3.00 T y( ) 23 3x 3385 D a
5250 R =o.8037 ’U,-—-—-=r‘1l
9 ' T n ”3,—1

a, .—
43 2'00 d1— 13, 9 ..°—— - '9 ° a y (12) = -0.3521x + 2.0742
«A
o 1.50 2 ;
. . . _ _ R = 0.8444
4 £ ‘ J "‘H‘W"1"3"“'A"a--A--a--5.A.
1.00

T 0.50 —~ ---————#-— ' .

1 2.20 2.40 2.60 2.80 3.00

1 Frequency (GHz)

 

 

 

 

Figure 6.48 Comparison of loss tangent of SAP Mixtures (65%)

6.6 Power Measurement

Amount of power measured by the antenna which was nearly similar to amount of power
received by the RFID transponders. The radiated power was measured using the setup
shown in Figure 5.7. An RFID interrogator was connected with a linear or circular
transmitting antenna at a distance from 1 cm to 65cm. The transponders were placed at a
certain distance from the reader antenna oriented in the direction of horizontal and
vertical to the transmitting antenna. At each location, the power was measured using the
2-wire dipole antenna placed in the same location and orientation as the transponders.
The style of the transmitting antenna, the orientation of transponder (receiving two-wire
dipole antennas) and distance were the independent parameters. The power measurement
result showed in Figure 6.49 to Figure 6.62. It can be seen that power decaying along
with the distance quickly. Figure 6.49 showed as the distance increased, the received

power from reader antenna declined quickly. However, Power from linear antenna

99

declined faster in comparison with circular antenna, Regression analysis showed a small
R2 value (0.7883) in linear antenna in comparison with circular antenna. It implied the
radiated power received from linear antenna was unstable in comparison with the circular

antenna.

 

 

 

 

 

 

. . T
Companson of Received Power (SAP, 50%) i
T 0010000 T x Circular T
- 1 y (L)= -7E-05Ln(x) + 0.0003 + Linea, 1
,5 0.001000 ' R2 = 0.7883 — — -Log. (Linear) T
v 1% + j; - - - -Log. (Circular) T
I 11;) 0.000100 T“ _x‘ 4:;— _+. 1‘ _ ‘ ~ _
-& *.‘X.‘K‘+—f +~~+~3~4L +
. 0.000010 Ty(C)= -2§-05Ln(x) + 95365 x‘ 'r - x- - 1, . “a,“ 3
= . \ :
0.000001 8 09906 . 1 ‘ *
, 0 10 20 30 40 50 60
1 Distance (cm)

 

 

Figure 6.49 Antenna received power between reader antenna and tag

6.6.1 Antenna Style

Figure 6.50 showed the different inﬂuence of path loss in open-air with circular antenna
and linear antenna. For the circular antenna, changing orientation of the receiving antenna
from vertical to horizontal , the average receiving power decline 1.4ldB or 30%;
however, the power loss is linearly decreasing vs. distance. Figure 6.51 showed in linear
antenna, power was rapidly loss vs. distance while changing orientation of the receiving
antenna from vertical to horizontal. It presented in free space, linear antenna is serious
orientational selectivity. However, circular antenna has less orientational selectivity. but

changing the receiving orientation weaken the power transmission.

100

Power (dB)

 

 

 

Power (dB)

Power Attenuation in Open-air

 

 

   
      

 

 

 

 

A

-5.00 . . ___ - j
Y (V)= -0.2295x - 9.5738 0 vertical T ;

2 _ A honzontal .

.1000 R " 0'938 . - - - Llnear (horizontal) ,
Linear (vertical) T 1
1
1

-2000 y(H)=-O.2197x-11.299 1‘

 

-25.00 '~ - H
0 5

    
 

\

R2 = 0.9657

1

1O 15 20 25 30 35 40 45 50 55 60 65
Distance (cm)

1 l 1

Figure 6.50 Power decaying in open-air with circular antenna

 

 

Power Decaying in Free Space T
0 vertical T
0.00 ~ V (V): -0-2295X - 9.5738 a horizontal !
_ 2 _ — Linear (horizontal) 1
13.38 . R - 0.938 1 — mar (verma')

-4000 _ y (H)= -0.3776x - 20.549

 

-50.00 L a
o 5

 

     

R2 = 0.7611

4 l 1 1 L l P l l l l l

10 15 20 25 30 35 40 45 50 55 60 65
Distance

 

 

 

 

Figure 6.51 Power decaying in open-air with linear antenna

101

 

Tag Orientation Loss in Circular and Linear Antennae

 

  

 

 

 

 

 

 

 

 

29.00 — _ __ _
I I
24.00
A 19.00 1 - T
‘8 r _ I .
I 14 00 T . u ' l‘+acuar .
8 . T I Linear
A 9'00 Linear (cicular)T
400 T. Linear (Linear) T 1
1 __‘T T o. -22 I
'1.00 L A 4 1 1 l L i
0 1 0 20 30 40 50 60 70
Distance (cm)

 

Figure 6.52 Tag orientation loss in different antennas

6.6.2 Shielding

Figure 6.53 showed the power with aluminum shielding. In comparing with power in
free space, at the same distance, the power with the shielding decline about 23.92dB or
by a factor of 246. Obvious, the Al shielding did good job. Table 6.2 showed a deviation
of shielding effect among four conﬁgurations. Shielding effect presented the power
received by the power sensor was from the sample window only after the RF signal pass

through the SAP sample and the measurement was reliable.

 

V-C V-L H-C H-L Average
19.71 31.95 28.51 15.51 23.92

 

 

 

 

 

 

 

 

Table 6.2 Average shielding power loss (dB)

102

 

 

Power with Shielding

 

Power (dB)

5500 ~ - -—L-—~— .

 

 

+cv
+L-V
+0.11
+L-H

 

 

 

15101520253035404550556065

Distance (cm)

 

Figure 6.53 Power with Shielding

6.6.3 Circular Antenna

Figure 6.54 and Figure 6.55 were based on the power measurement in circular antenna. It
showed water is the major inﬂuence of power loss besides path loss. Figure 6.56
presented higher water content has a greater inﬂuence in power loss. Figure 6.57 and
Figure 6.58 showed that 70% water content has a strong inﬂuence to power, the average

power loss was 12.08 dB with the largest 14.15dB and smallest 9.85 which occurred in

the nearest and farthest location respectively.

103

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

1 Power Attenuation vs. Distance, Horizontal, Circular
T '10 TX~ w—m
‘X~ .x _ x
e A -15 : . - \ 2. T ~13 45*
T m T‘ D ‘33- :8"! \X’ -—>K. - -50%
1 '3 -20 V.- 0— N2». 81-8. ’52 «or
1 L ‘ . 4-0“ 9-“3 . x"*"*~-x_x _x “-55"
0;) '25 a o i- “ \". \ It.“ : ”"8“ ‘3‘-B-rl.”§_;“ - 5 +60%
8 -30 . ‘ _ :‘ﬁq‘f- ' g5: ' «'1»..- _. ...m
T -35 ~ °— ° N). IAN, 79743.10, 5 +7“
1 8, ‘°' K ~41 . "'7“
1 (u ’40 F .</ 5 1‘? ' r _.E 40%
T h
| g -45 h —o -85%
T < -50 — —c1— 90%
45%
_55 1 1 4 1 1 1 1 l l 1 1 l lob“
0 5 101520253035404550556065 -*-°l'"
1 Distance (cm)
Figure 6.54 Power attenuation of circular antenna (H)
1 Power Attenuation vs. Distance, Vertial, Circular
0 . +40%
1 -5 f0 ——0— 45%
: 8 -1o ‘ xi“<>~\ . .... .50..
i 13' -15 ‘§‘ 8:? 7% _ g_ —x— 55%
‘g’ 20 _ " ”‘ _ wrg-‘W —+ -°°*
o. -25 '~ ~ ~1__
.1 “5::
1 g -35 ~ (__I‘ _m
< '40 '0 —o -85%
'45 \0’ ~o- 00%
'50 P I T g‘ 1 —l— 1 1 I l l q .95“
o 5 10 15 20 25 30 35 4o 45 50 55 60 65-.-oo..
1 Distance (cm) '5‘ op”

 

Figure 6.55 Power attenuation of circular antenna (V)

 

 

 

Figure 6.56 showed received power in 50% water SAP sample was much larger than that

of with 75 % water SAP. Obvious, Higher water content leads to a lower power

104

receiving. Figure 6.57 showed in comparing with free space, with a 70% SAP sample,

average 15 dB power was lost in the measurement.

Power Attenuation in Circular Antenna T

 

 

1.015-04
9.105-05
8.105-05

1 A 7.105-05 g-

1 v 6.105-05 '-

" 5.105-05 T

4.105-05 »

3.105-05 1-

2.105-05 Ta

1

  
  
  
   

 

T o 50% .
o 75% T
Log. (50%)1

;_—_-—Log.(75%)T

W

 

 

Powe

 

 

1.10E-05
1.00E-06 ‘5

0 5101520253035404550556065
Distance (cm)

 

b- ___. —___

 

Figure 6.56 Power loss in 50% and 75% SAP

 

Inﬂuence of Water content on Power

 

0.00 1“ *~

5.00 ~

-10.00 T

-1500 »

-20.00 1..

-25.00 T ‘ A .

-30.00 - ‘ 4» --

T -35.00 » ‘ A» , o “

40.001-514-

15101520253035404550556065

T Distance (cm)

 

7+ free space
T+ 70% SAP

   
 

 

 

Power (dB)

 

 

 

 

 

 

Figure 6.57 Inﬂuence of water content on power loss

105

 

1 Average power loss with 70% water content

 

Loss (dB)
8

 

0 1 1 1 1 1 1 1 i 1 1 l 1 1

15101520253035404550556065
distance(cm)

 

 

Figure 6.58 Average power loss in 70% SAP specimen

6.6.4 Linear Antenna

 

 

 

 

 

 

 

 

Power Attenuation vs. Distance. Horizontal, Linear '+ 40%
: -10 T— ——n- 45%
T -15 >i<~ - -A- .5091
T g .20 x¥\ —x— 55%
i T: - q—“M-, --——x— 60%
T 0;: 25 ‘g'\ ‘ ‘XW 0 o—esei
i o '30 '3‘ D \. b _-
o. '10." ‘A .‘ , -. '25, - 87% . A , —+—70%
81-35 ’7 'o' "'1 "‘\%:ﬁ‘0_ ".U '« 7591.
g 40 9 VS}. "$.33? $1: “In-\i’l‘r/ —: .8096
> -45 ‘ . .. 1 1 '-~5|<‘- ‘ '1‘
T < o -O I. . u 0 ‘ .’ ..,. 4' 4;; .
_50 .O-A ’ T _0,:'/ _° 85*
T m ' ' ‘ ——o — 90%
T -55 f A 1 ‘ ‘ ‘ 4 4 T 1 A T q -95%
. 0 5 10 15 20 25 30 35 40 45 50 55 60 65 +0“,
1 Distance (cm) _‘_ op...
L ......

 

Figure 6.59 Comparison of power attenuation with saturated SAP samples

106

 

 

 

 

 

PowerAttenuation vs. Distance. Vertial, Linear ° “0%
—— o— 45%
0 ‘ "—— ‘ - -A- .5099
-5 Xxx
A "' A — 55%
1 % -1°-* Magi-X ' hm
:: -15 16.1?" tr’tj'--.>1<.-.>K-.x.,x,i a 1+
1 g '20 1 . {{‘g‘K—‘Ju‘ 'VA‘ _7" (j— U7 a" “E? é‘rx —o—- 85%
1 8 -25 ‘ ° ’ ’z‘ik/RQW'A‘ , m
l o '30 ‘ '3 2 '9 3
' S '35 p . -" ' O 75%
a), '40 q I”
w < -45 ; 5
i -50 fr I -o was 1
-55 m1 1% 1 1 1 1 1 1 _D__m
0 5101520253035404550556065 “-95%
Distance (cm) *0“, :
,mﬁf -1 l

 

 

 

Figure 6.60 Comparison of power attenuation with saturated SAP samples

 

 

 

 

 

 

 

 

 

Power Attenuation in Linear Antenna
4.00E-O4
g 1 o 50:
3005-04 ~ 2 l '3 75
‘A ° R =0.788 l ---Loo-(50%)
; E, ‘\ 3 ; Log. (75%)
E 5 2005-04 9 \
3 \ o
1 (E \ \
l 1005-04 ~ ‘ ~. \
, 2 _ 5 ~ \
' R D— O 630 0 9“ - ~ ~
1 ° 0 ~6‘ _
1 1.00E-08 1 "
O 10 20 30 40 50 60 70
Distance (cm)

 

 

 

Figure 6.61 Comparison of power attenuation with 50% and 75% water content

Figure 6.61 showed in a linear antenna , receiving power was less in a 50% sample in

comparing with in higher water content sample (75%).

107

5.01 505

2.01 E-05

Power (w)

1.01E-05 ~

1 .00E-07

 

4.01 E-05 ~

3.01E-05 »

 

1 Power Attenuation of 75% SAP with antennae

 

 

 

 

 

D
2 i Circular
\ R =0.6309 I Linear
\ ----- Log. (Circular)
\ U - — -Log. (Linear) __JI
P. 0\
. \
s. \
“o‘.\°‘~\
2 ‘°"P--:°.‘B ~~~~~
R =9-9055? ?°'?"'9'-9--F-TQTIj—;y
O 5 10 15 20 25 30 35 40 45 50 55 60 65

 

Distance (cm)

 

 

 

Figure 6.62 Comparison of received power with circular and linear antenna

6.7 Critical Power

Table 6.4 showed the relationship of half decaying rate (HDR) of readability and least
power according to the power measurement and readability survey in free space. If the
power less than -23.32 dB, the transponders supposedly do not respond to the reader or
the reader can not pick up the backscatter signal at all. However, in the power

measurement, even if the power was more than -23.32dB, the readability was 0 percent

with a high water content SAP sample.

 

Half decaying rate

100%

50%

25%

12%

6%

3%

0%

 

Least power (dB)

 

 

-8.lS

 

-l4.39

 

48.34

-l8.56

 

 

-21.10

 

-22.23

 

-23.32

 

Table 6.3 Half decaying rate of readability and least power in free space

108

 

6.8 Readability Survey

When performing the readability survey, the more RFID tags were tested; the average
readability data would trend to the reality due to the tag response to critical signal
strength may vary, as each of read is crucial to statistically analyze the effect of water
content. The following graphs present the readability model in the test. Alien ALL-9238

Squiggle Class] 64 Read/Write UHF tags were used in the test.

6.8.1 Readability Decaying Model in Open-air

Figure 6.63 showed a tag readability decaying model in open-air with four tag and reader

combinations:
1. Linear reader antenna with horizontal tag
2. Linear reader antenna with vertical tag
3. Circular reader antenna with vertical tag
4. Circular reader antenna with horizontal tag

The graph really indicates that different reader and tag combination gives different tag
readability even if the other conditions are the same. Obvious, Well packaging operation
and conﬁguration will create higher readability and system performance. In the
combinations, the readability decreased quicker while the tag orientation changed from
vertical to horizontal. For circular antenna, the orientation effect is small, however, it

still decrease tag readability while the tag orientation has been changed.

109

 

 

   
  
 
 
  
     
 

 

 

 

 

 

Tag Readability Decaying Model in Open-air
i 100 .- .
A D W
§ 9° — -A- L/Hl
' g 80 x CN
1 e I x cm
I a, 70 - - - Poly.
'8 60 ------ Poly. C I I
ciz’ 50 ----Poly. C/H .
. El ,
40 “x
\
30 ; Cl \D-\
20 I ‘X. ~ Q\
10
0 L_ _ __
1 0 5 10 15 20 25 30 35 40 45 50 55 60 65
Distance(cm)

 

 

 

Figure 6.63 Readability decaying in free space

6.8.2 Tag Orientation

Figure 6.64 showed readability decaying model in different tag orientation with 50%
water in SAP sample and a linear antenna. Linear antenna had strong polarization,

changing antenna polarization caused a 10 time readability declines.

llO

 

 

 

 

 

 

 

 

 

I Readability in SAP (50%) with a Linear Antenna

7o
1
l I; k ‘
‘95 5° 5 \° 2
I; 40 :_ ‘R =0.9799
1 E l \ I
E§ 30 ° [ 0 Vertical 7' 1
l I \
!& 20 I- ‘ 'I 0 Horizontal

10 I R2 = 0.8289 0\ ~ — - Poly. (Vertical) .
I 0 it 13" — ‘0‘ . — -Poly. (Horizontal),
o 10 Distance2(9:m) 3° 4°

 

Figure 6.64 Comparison of readability: tag orientation

6.8.3 Water Content

Figure 6.65 to Figure 6.71 showed the major inﬂuence of water content on readability, as

water content increase, the readability decline fast.

[11

70 ~—— ——
60 . ,
g 40 e i i
g 30 ‘ y = -67.692x + 59.026
32 I R2 = 0.4781
20 2»
l
10 } I
01_________ _ . g t
40% 50% 60% 70% 80% 90%
Water oontent(%)
Figure 6.65 Readability fading
Readability vs. water content 1
8° F r ‘ " a I
70 3 l2“. ‘ 1
. I A 10cm I
2: 60 ° I x 15cm I
as 50 c1 . ----- :03. i3;
.0 ‘ O .
g 40 —-- -Po|y.(10cm) I!
- — -P I . 15
20: e~~ ----------
10 I \ ‘ A ‘ ‘ ......
0 I--- L__¥___._ 1“—

 

Vertical Tag Readability at 1 cm with a linear antenna

 

         

 

 

 

 

 

 

 

 

 

 

 

 

 
  
  
 

 

 

 

 

40% 45% 50% 55% 60% 65% 70%

Water content

  
    

 

 

Figure 6.66 Comparison of readability (I)

”2

 

Readability vs. water content

 

 

 

 

35 —— —— eeeeee W
30 » .._ _ “LI I

I K3 25 L . o 1cm I
I 2., E I A 5cm

g 20 i— 3 ----- Poly. (1cm)I

g 15 V 3 POIY.(5CM)1
l g 10 I

T A

 

 

 

 

40% 50% 60% 70% 80% 90%

 

water content

 

Figure 6.67 Comparison of readability(ll)

 

 

 

Readability vs Water content

 

 

 

 

 
 

35- 1 ~~ :
30~ I". 1cm
0 5cm
25.
13201 :
N ‘ I
lglsl
:&> A

o
o‘.
.

 

_a
O 01 o
_ T. I

Q
'0.-

40% 45% 50% 55% 60% 65% 70% 75% 80% 85% 90%
Water content

 

 

Figure 6.68 Comparison of readability(lll)

ll3

._ __- 'I _-

 

 

RFID Tag Readability vs. Water Content ( Circular/
Vertical Tag)

Readability (%)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

0 Q ~, .1“ .
40% 50% 60% 70% 80% 90%
Water Content
Figure 6.69 Comparison of readability(IV)
Readabilty vs. water content
35 I— ——---—— -- -— —- 1
I .. N I
' 25 ’ =1
I g F \ R2=O.9068 . x 5cm '
5 20 1 I
g \ I— -Poly.(1cm)
315 i ><\ ‘- - -Poly (5cm)I
a: I .
10} R2=O.5304 \ L '- —
5 x . . - ' ‘ - a-\.§~_ A
O , ,____ mg 1 Q x My);
40% 50% 60% 70% 80%
Water Content

 

 

 

Figure 6.70 Comparison of readability(V)

ll4

Readability (%)

 

Readability vs.Water Content at 1 cm I

 

 

 

 

 

 

70 _ — I i
60 I Q ...°.'I.LN I
5.: 140+ I
40 I i —A——CN i
r 0‘. I —-x——C/H I I
30 I. “x '. l
I “ x. z
20 I '. -'\\ . i
i ‘5 ‘ﬂ '. i
10 . A \\ 0..“ Mo 1
0 LB J . D— 3%.}‘123 ~~£~::ﬁ ~
40% 50% 60% 70% 80% 90%

Water content I

 

Figure 6.7] Comparison of readability(Vl)

115

 

Chapter 7

CONCLUSIONS

This thesis provided a material characterization methodology using waveguide and
network analyzer for determination of the water contribution in dielectric properties by
measuring S-parameters of a serial of saturated superabsorbent polymer with different
water content to simulate wide range of real products in supply chain. Further, this thesis
described tag readability survey and power measurement methodology using power
sensor and a 2-wired folded dipole antenna as receiving antenna to determine the
effective receiving power level of RF signal radiated through the SAP specimen from
RFID reader. A series of tests and measurements were developed with saturated

superabsorbent polymer in the laboratories.

7.1 Material Characterization

The permittivity of hydrated SAP mixtures were extracted by using an iterative complex
two dimensional Newton’s root-searching algorithm with the experimental S-parameters

obtained from a vector network analyzer.

Further statistical and correlation analysis revealed when the water content increased in
the hydrated superabsorbent polymer sample, the S-parameters had a slight augment over
the frequency range from 2.2GHz to 3.0 01-12. As a result of the extraction, the dielectric
properties in term of dielectric constant and loss factor of the hydrated SAP specimens

had a distinct inﬂuence from water content. The relative permittivity has been raised with

116

an increasing of water content in saturated superabsorbent polymer. it showed a nearly

linear relationship between water content and relative permittivity.

7.2 Received Radiated Power

Power measurement shows major inﬂuence from the water content, the higher water
content in the sample, the higher power loss measured with the same polarization of
receiving antenna at the same location. Nonetheless, the power decay presented logarithm
regression with the distance. In comparing with path loss in free space, there were larger
ﬂuctuation of power loss in higher water content sample. The power measurement
presented that the power level received through high water content sample was far less
than the power level received through free space, furthermore, it was less than minimum
critical power for RFID tag in the research. Obvious, no tag responding to reader was

expected in this situation.

7.3 Readability

Readability study was compared with inﬂuence on water content, distance, tag
orientation and antenna style. It strongly showed that the tag readability depended on tag
orientation, antenna polarization and distance from the RF sources. Orientation or
polarization attenuated at least 15 dB power or average 19 dB in linear antenna. The
20dB attenuation with polarization observed agree well with the literature. However,
circular antenna attenuated about 1.41dB or about 30% signal loss which reduced the
readability with an acceptable level. The tag readability in the different samples also
shows this tendency which agreed well with the experimental results. The study also

showed that the power level is a necessary condition but not a sufficient condition. With

117

 

the same power level, the readability was various. Obvious, other factors may get

involved with readability, such as the sensitivity of tags etc.

This scenario showed though there were pretty much undetermined inﬂuences from
RFID implementation, determination of inﬂuences of water content in products and
polarization in tag and reader antennas were high priority for successful RFID
implementation. Potential inﬂuence of product content itself on RFID system
performance and stability is not a neglectable factor with RFID application in supply
chain. Recognizing the inﬂuences of your products and conﬁgurations on RFID system
is the key to the proper implementation of the RFID system and elimination of negative
effects to RF ID readability, which meets the bottom line of feasibility RFID solution. It
was hypothesized that improving packaging operations in supply chain may enhance the
stability and performance of deployed RFID system. However, the inﬂuence of product
content on tag readability such as, water, salinity, temperature which may cause a low
readability is unable to be dispelled completely. Therefore, the system performance and

stability will hard to reach the imposed implementation guideline.

7.4 Limitations of This Research

There are several factors that could be limitation for this research. The necessity for
further validation and independent analysis of the measurements in this research was
emphasized. In material characterization, measurement frequencies, 2.2 GHz to 3.0 GHz
were involved, however, the prevalence frequency range of RFID systems in supply
chain is 860MHz to 960MHz. Though the tendency of dielectric properties in UHF and
VHF are pretty similar, the specific characteristics of the saturated SAP samples at

860MHz to 960MHz in this research was not determined. Power measurement was

118

conducted in an open area test site (OATS) to simulate a typical supply chain
environment. Consequently, the test laboratory is not a anechoic chamber may get
involved with outside interference which may reduce data conﬁdence of power
measurement. Further more, the hundreds of tested RFID tags showed variety sensitivity
to reader and different read ranges though all the tags were passed the single mode
readability test. The distinction issue of tag performance was mentioned in literature as

well [10], which should be removed in future study if possible.

7.5 Future Research

A number of factors inﬂuence the performance and stability of RFID in different
application environments. Future work include material characterization in 860MHz-
960MHz to match the 915MHz RF ID technology in supply chain. In range of 0.75GHz
to 1.12 GHz, WR975 waveguide can be used for material characterization [57]. However,
due to the larger cross-section size in WR975 waveguide (9.75inch *4.875 inch) in
comparing with WR340 waveguide, the sample preparation procedure will be a larger
challenge for homogeneity and density stability. Therefore, Wide bandwidth
measurements of the materials using the coaxial probe are recommended for UHF high
permittivity materials. Consequently, material characterization of dry SAP powder or
particles will be perfect supplement to describe the undulation of dielectric properties.
Simultaneously, the measurement of conductivity( 0 ) in the material is another
interesting area to understand the inﬂuence of product content on RF ID performance and

stability.

119

 

According to the results from this research, people may have anxiety whether their
products can be "RFID signal compliance", which will give their "peace of mind" or '
"nightmare" in implementation of the RF ID systems. Obviously, the special investigation
should be conducted before a reliable RFID solution was deployed in supply chain.
Therefore, a research of consummating the "RFID signal compliance" test and procedure

for industry will be a perfect project.

Back to this research, in power measurement, determination of receiving antenna
speciﬁcations will provide more accuracy and reliable correlation to tag response
behaviors. Improving sample preparation procedures will provide more converge result.
Some error analysis in measurement may also be useful. Tolerances checking on sample
thickness, density should be helpful. these aspects are feasible future investigations.
Furthermore, dual power sensor measurement will provide simultaneous effect of tag
orientation or antenna polarization and reduce the errors due to DUT mobility during the
measurement. Again, a better size matched dipole antenna to RFID tags for power sensor
will provide vicinal tag status in pallet load test. Certainly, Improving the automatic data
acquisition procedures will reduce the human interference in the measurement. These

issues and improvements should be nice for future research in RFID.

7.6 Summary Conclusion

This research was of distinct signiﬁcance as it was the ﬁrst study concerned on
differentiation of inﬂuence of water content in products on RFID performance and
stability through simulation tests and measurements of saturated SAP mixtures
undertaken so far. The methodology provided theoretical accuracy and practical

maneuverability through affiliation of material characterization, power attenuation and

120

 

readability in the same sample of the saturated material. The results of the research will
help us acknowledge the inﬂuence of product content and packaging operations on
successful implementation of RF ID in supply chain. Meanwhile, the methodology in the
research will easily be adopted by the RFID project initiative in industry. However, it
should be realized that the results of the tests must be reviewed when the set up and test
conditions have been altered. Even in the same condition, the difference of homogeneity
of the saturated material may lead to a different result due to deviation of the structure,
density, salinity in the two phase mixtures. To determine the inﬂuence of your special
products on RFID implementation, a consistent procedure carried out under the special

environment will be appropriate.

121

 

Appendix A
S-Parameters in Saturated SAP (90%)

Notes: Respectively, S] 1, $21, $12, 822. Total points: 20] for one S-parameter.

CITIFILE A01 .01

#NA VERSION HP8510C.07.lO

NAME MEMORY

#NA REGISTER l

VAR FREQ MAG 201

DATA S RI

COMMENT YEAR MONTH DAY HOUR MINUTE SECONDS
CONSTANT TIME 2005 05 25 13 56 45.0
BEGIN

~9.27337E-l,0.68634E-l
-9.250|8E-l,0.68847E-l
-9.23584E-l,0.68664E-l

-9.2| 875 E- l ,O.68450E-l

-9.2|600E- 1,0.69274E-l

-9. l8823E- l ,0.68267E-l

-7.76092E-1,-0.2954lE-l
-7.76l53E-l,-0.30456E-l
-7.77221E-l,-O.30883E-l

END

CITIFILE A01 .0]

#NA VERSION HP85l0C.07. 10
NAME MEMORY

#NA REGISTER 2

VAR FREQ MAG 201

DATA S RI

COMMENT YEAR MONTH DAY HOUR MINUTE SECONDS

122

CONSTANT TIME 2005 05 2513 46 21.0
BEGIN

-7. l 9642E-2,-7.20443E-2
-7.43408E-2,-7.24372E-2

-7.67822E-2,-7.273 l OE-2

-l .78955E- l .0.50468E-l
-l.78482E-l,0.52635E-l

- l .78321E-l,0.54206E-l

-0.88989E-l,l.5856lE-l

-0.87554E- l, l .59 l 49E-l

-O.86l58E-l,l.59393E-l
-0.84953E-l,l.600l8E-l

END

CITIFILE A01 .01

#NA VERSION HP8510C.07.10

NAME MEMORY

#NA REGISTER 3

VAR FREQ MAG 201

DATA S RI

COMMENT YEAR MONTH DAY HOUR MINUTE SECONDS
CONSTANT TIME 2005 05 25 12 13 47.0
BEGIN

-7.l9833E-2,-7.18383E-2

-7.48 lOOE-2,-7.21626E-2
-7.68966E-2,-7.247l6E-2

-7.92465E-2,-7.24487E-2

-0.87753E-l,l.59l4lE-l
-0.86448E-l, l .59812E-l
-0.85166E-l,l.60270E-l

END

I23

CITIFILE A.Ol .01

#NA VERSION HP8510C.07.10

NAME MEMORY

#NA REGISTER 4

VAR FREQ MAG 20]

DATA S RI

COMMENT YEAR MONTH DAY HOUR MINUTE SECONDS
CONSTANT TIME 2005 05 25 13 34 30.0
BEGIN

-7.66296E-l,5.41503E-l
-7.60986E-l,5.489l9E-l
-7.52807E-l,5.53070E-l

-7.39837E-l,5.59l43E-l

0.33 l72E-l ,7.83386E—l
0.36315E-l,7.84545E-l
O.38848E-l,7.86224E-l
0.40435E-l,7.85858E-l
0.43 823 E-l ,7.84484E- l

124

 

Appendix B

Experimental Permittivity and Permeability

FREQ(GHz), Re(EPR-F}, lm{EPR-F}, Re{MUR-F}, lmlMUR-F}, Re{EPR-R}, Im{EPR-R}, Re{MUR-R}, Im{MUR-R}
0.2200E+Ol_ 0.2286E+02, -.l767E+02, 0.962|E+OO, -.4695E-02, O.2140E+02, -.l82lE+02, 0.1029E+0|, -.2946E-Ol
0.2204E't01, O.2275E+02, -.l758E+02, 0.96l9E+00, -.1276E-Ol, 0.2182E+02, -.l786E~t02, 0.lOOSE+Ol, -.3703E-Ol
0.2208E+0l, 0.2273E+02, -.l746E.+02, 0.9551E+00, -.78llE-02, 0.2200E+02, -.l790E+02, O.9943E+00, -.2231E-Ol
0.2212E+0|, 0.2277E+02. -.l736E+02, 0.9587E+00, -.l544E-Ol, 0.219IE+02, -.l844E+02, 0.1020E+0l, -.752|E-03
0.2216301, 0.2276E+02, -.l720E+02, 0.9582E+00, -.l764E-0l, O.2l64E+O2, -.l872E+02, 0.1045E+Ol, 0.8l39E—02
0.2220E+Ol, 0.227SE+02, -.l70lE+O2, 0.9584E+00, -.2090E-Ol, 0.2I52E+02, -.l9l9E+02, O.l062E+Ol, 0.ll$2E-Ol
0.2224E+Ol, 0.2290E+02, -.l708E+02, 0.9574E+00, -.l260E-Ol, O.2l82E+02, -.l943E+02, 0.106lE+Ol, 0.347lE-Ol
O2228E+0L O.2288E+02, -.l695E+02, 0.9580E+00, -.l460E-Ol, 0.2]69E+02, -.l95|E+02, O.lO69E+01, 0.3449E-0l

O.2232E+Ol, 0.229lE-t-02. -.l706E+02, 0.9586E+00, -.8268E-02, 0.2l51E+02, -.l944E+02, 0.lO7IE+0l, 0.3024E-0l

0.2956E+Ol, 0.2l65E+02, -.l350E+02, 0.9159E+00, -.6343E-01, 0.2103E+02, -.l680E+02, 0.9626E+00, 0.3999E-Ol
O.296OE+01, 0.2165E+02, -.l339E+02, O.9l58E+00, -.66SZE-Ol, 0.21l2E+02, -.l690E+02, 0.9606E+00, 0.4482E-0l
O.2964E+Ol, 0.2177E+02, -.l344E+02, 0.9ll9E+00, -.62|2E-Ol, 0.2]08E+02, -.l692E+02, 0.96l5E+00, 0.4SIOE-0l
O.2968E+Ol, 0.2173E+02, -.l345E+02, O.9l48E+00, -.6334E-Ol, 0.2090E+02, -.l7llE+02, 0.9678E+00, 0.5137E-0l
0.2972E+0l, 0.2164E+02, -.l354E+02, 0.9203E+00, -.602lE-Ol, 0.2090E+02, -.l7l3E+02, O.9680E+00, 0.5263E-Ol
O.2976E+0l, 0.2l66E-l-02, -.l356E+02, 0.9I9SE+00, -.6088E-0l, 0.2079E+02, -.l692E+02, 0.9702E+OO, 0.4SOlE-Ol
0.2980E+Ol, 0.2092E+02, -.l4l3E+O2, 0.950lE+00. -.5439E-Ol, 0.2007E+02, -.l662E+02, 0.lOO9E+0l, 0.3753E-Ol
0.2984E+Ol, 0.217lE+02, -.l332E+02, 0.9137E-l-00, -.6476E-Ol, 0.2103E+02, -.l705E+02, 0.9656E+00, 0.5034E-Ol
0.2988E10l, 0.2159E+02, -.l335E+02, 0.9197E+00, -.674OE-Ol, 0.2098E+02, -.l7l7E+02, 0.9655E+00, 0.552lE-01
0.2992E+Ol, 0.2155E+02, -.l335E+02, 0.92OIE+OO, -.67l3E-01, 0.2100E+02, -.l720E+02, O.963lE+00, 0.5641E-01
0.2996E+Ol, 0.2155E+02, -.1326E+02, 0.9197E+00, -.6945E-01, 0.2107E+02, -.I708E+02, 0.9609E+00, 0.5305E-01

0.3000E+Ol, O.2|56E+02, -.l324E+02, 0.9]94E-l-00, -.6928E-0l, O.2087E+02, -.l7llE+02, 0.967OE+00, 0.5528E—Ol

125

Appendix C
Glossary

Cutoff frequency For a given transmission mode in a nondissipative waveguide, the

frequency at which the propagation constant is zero.

Dissipation The power reduction in a transmission path caused by resistive or conductive

loss, or both.

Gain The power increase in a transmission path in the mode or form under consideration.

It is usually expressed as a positive ratio, in decibels.

Incident wave At a transverse plane in a transmission line or waveguide, a wave

traveling in a reference direction.

Loss The power reduction in a transmission path in the mode or modes under

consideration. It is usually expressed as positive ratio, in decibels.

Port (for a waveguide component) A means of access characterized by a speciﬁed
reference plane and a speciﬁed propagating mode in a waveguide which permits power to

be coupled into or out of a waveguide component.

Reﬂected wave At a transverse plane in a transmission line or waveguide, a wave
returned from a reﬂecting discontinuity in a direction opposite to the incident wave.

(Compare incident wave)

Reﬂection coefﬁcient At a given frequency, at a given point, and for a given mode of
propagation, the ratio of some quantity associated with the reﬂected wave to the

corresponding quantity in the incident wave.

126

 

Reﬂection loss (gain) The ratio of incident to transmitted power at a reference plane of a

network.

Return loss (gain) The ratio of incident to reﬂected power at a reference plane of a

network.

Skin depth Of a conducting material, at a given frequency, the depth at which the surface

current density is reduced by one neper.

TE mode (H mode) A waveguide mode in which the longitudinal component of the
electric ﬁeld is everywhere zero and the longitudinal component of the magnetic ﬁeld is

not.

TEM mode A waveguide mode in which the longitudinal component of the magnetic

ﬁelds is everywhere zero.

TM mode (E mode) A waveguide mode in which the longitudinal component of the
magnetic ﬁeld is everywhere zero and the longitudinal component of the electric ﬁeld is

not.

Waveguide A system of material boundaries or structure for guiding electromagnetic
waves. Usually such a system is used for guiding waves in other than TEM modes. Often,

and originally, a hollow metal pipe for guiding electromagnetic waves.

127

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