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This is to certify that the

thesis entitled

Internal Organizational State Sensing for
Magnetorheological Fluids

presented by

Miguel Omar Hayes Michel

has been accepted towards fulfillment
of the requirements for

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MSU leAn mmw Opportunity Intuition

INTERNAL ORGANIZATIONAL STATE SENSING FOR
MAGNET ORHEOLOGICAL FLUIDS

By

Miguel Omar Hayes Michel

A THESIS
Submitted to
Michigan State University

in partial fulfillment of the requirements
for the degree of

MASTER OF SCIENCE

Department of Mechanical Engineering

1997

ABSTRACT

SENSING OF INTERNAL ORGANIZATIONAL STATE OF
MAGNETORHEOLOGICAL FLUIDS

By

Miguel Omar Hayes Michel

Physical properties of MR fluids respond a non-linear, hysteretic, time-
varying function to direct magnetic field excitation. Physical properties of MR
fluids are a function of suspended particle organization. Precise MR fluid
response requires control of the particle organizational state of the fluid through
the applied magnetic field. A reliable sensor of the state of the fluid is needed

to implement precise MR fluid response.

Permeability, resistivity and perrnitivity changes of MR fluid were
investigated and their suitability to indicate the organizational state of the fluid
was determined. High sensitivity of perrnitivity and resistivity to particle
organization and applied field was proved experimentally. The measurable
effect of these material properties, capacitance and resistance, can be used to

implement a MR fluid state sensor.

Copyright by
Miguel Omar Hayes Michel
1 997

To Miguel and Karim

ACKNOWLEDGMENTS

The most sincere thanks to Dr. Clark Radcliffe for given me the opportunity
to get into the research world. Tanks to Dr. Clark Radcliffe, again, and Dr. John
Lloyd for awarding me with a Research Assistantship to accomplish this
theses. Thanks to Charles Birdsong and Brooks Byam, graduates students
and Dynamics System Laboratory administrators, for their help and friendship.
Thanks to Kara Mc Gregor, Yinxue Su on the cotrollable fluids research group.
And special thanks to Yinxue Su, Yihong Zhang, Jae-Man Cho, Chirs House
and Polarit Apiwatlanalunggarm for their support and friendship through this

two years.

TABLE OF CONTENTS

List of Tables .............................................................................................. viii
List of Figures ............................................................................................. ix
Introduction .................................................................................................. 1
Magnetorheological Effect ........................................................................ 5
Sensor Development ................................................................................ 7
Inductance Testing .................................................................................... 9
Experimental Setup for inductance measurements ........................... 11
Inductance measurements ...................................................................... 12
Capacitance Testing ................................................................................. 15
Resistance Testing ................................................................................... 16

Experimental Setup for capacitance and resistance

measurements ........................................................................................... 17

Capacitance measurements ................................................................... 18
Resistance measurements ..................................................................... 20
Sensitivity of inductance, resistance and capacitance ....................... 22
Conclusions and Recommendations ................................................... 23
Appendix - Inductance Measurement LabView Program ................... 27

Appendix - Inductance response to a square wave field

excitation ...................................................................................................... 29

Appendix - Relative properties change as a function of applied

field ............................................................................................................... 30

Bibliography ................................................................................................ 31

vii

LIST OF TABLES

Table 1.- Sensitivity of magnetic and electric properties. ................... 23

viii

LIST OF FIGURES

Figure 1.- Non energized and energized particle orientation and

positioning ..................................................................................... 3

Figure 2.- Internal particle organization of MR Fluid as a

function of applied field ............................................................... 6

Figure 3.- MR Fluid Device for measurement of (a) static and (b)

moving fluid. .................................................................................. 8
Figure 4.- Three voltmeters method to compute Inductance .................. 10
Figure 5.- Experimental setup for inductance measurement ................. 11
Figure 6.- Inductance vs. applied field. ....................................................... 13
Figure 7.- Inductance vs. MR fluid flow ........................................................ 14
Figure 8.- MR fluid core inductor .................................................................. 14
Figure 9.- MR fluid core Inductance vs. time. ............................................. 15

Figure 10.- Experimental setup for Capacitance and Resistance

measurements ......................................................................... 16

Figure 11.- Equipment setup for capacitance and resistance

measurements ........................................................................... 18

Figure 12.- Parallel equivalent capacitance as a function of

applied field ................................................................................. 18

Figure 13.- Series equivalent capacitance as a function of

applied field ................................................................................. 19

Figure 14.- Parallel equivalent Resistance as a function of

applied field ................................................................................. 20

Figure 15.- Series equivalent resistance as a function of applied

field. .............................................................................................. 21

Figure 16.- Front Panel. LabView Inductance measurement

program. .................................................................................... 27

Figure 17.- First Frame. LabView Inductance measurement

program. .................................................................................... 27

Figure 18.- Second Frame. LabView Inductance measurement

program. .................................................................................... 28

Figure 19.- Third Frame. LabView Inductance measurement

program. .................................................................................... 28

Figure 19.- MR fluid response to a magnetic field square wave ...... 28

Figure 20.- Relative properties change as a function of applied

field. ............................................................................................ 29

NOMENCLATURE

State variable vector
Sensitivity of Q respect to H
magnetic permeability [ H/m ]

Phase angle [ °]

perrnitivity [ F/m ]

resistivity [ M Q - m ]

Cross section [m‘2]

Magnetic field density [Gauss]

Capacitance [ F]

distance [ m ]

Alternate voltage amplitude [V]

Alternate voltage amplitude across the resistor [V]
Alternate voltage amplitude across the inductor [V]
Frequency [ Hz]

Magnetic field strength [kA/m]

Inductance [ mH ]

Length [ m ]

xii

R1

number of turns on the winding
resistance [ Q]
constant resistance (19)

general input

general response

xiii

INTRODUCTION

Magnetorheological (MR) fluids, are often called intelligent or smart fluids,
because the rheology of this fluids can be changed reversibly, by applying an
external magnetic field. An MR fluid is a suspension of micron-sized magnetic
particles dispersed in a fluid carrier such as a mineral I silicon oil or an
aqueous solution. Abroad range of possible applications that would use the
rheology property of this fluid to enhance devices performance is the reason for

the increasing research interest in these fluids.

The physical properties of an MR fluid change as a non-linear time-varying
function of applied field. MR fluids also show the typical hysteretic behavior of
magnetic materials. The external magnetic field applied to the MR fluid causes
changes of physical properties of the fluid, e.g. electrical conductivity, thermal
conductivity, permeability and viscosity. If the MR fluid response can be sensed

electrically, the above physical properties can be controlled.

Vlfinslow (1947) is generally credited as the first person to recognize the
potential of controllable fluids in the 1940's with the first electrorheological (ER)
fluids patent paper describing the ER effect. MR fluid discovery can be credited

to Jacob Rabinow (1948) at the US National Bureau of Standards. in the

2
1940's. Interestingly, this work was almost concurrent with Winslow ‘s, ER fluid
work. The late 1940s and early 1050s actually saw more patents and
publications relating to MR fluids than to ER fluids. While Rabinow’s work is
largely overlooked today, WII'ISIOW discussed the work on MR fluids going on at
the National Bureau of Standards in his seminal paper on ER fluids. In the near
past, studies have focused on the viscosity of MR fluids as a function of a

induced field.

Viscosity has proved to be very sensitive to changes on external magnetic
field (Shulman 1985, Kordonsky 1993). Viscosity dependence on particle
concentration, particle shape, size and material in combination with several
fluids carriers have been evaluated. Despite the high sensitivity of viscosity, real
applications are rare (Rheonetic’s linear damper, rotary brake and vibration

damper).

Control of the viscosity on current MR devices is performed by direct
excitation of the external magnetic field. The non—linear, hysteretic, time-varying
response of the fluid is an obstacle to precision viscosity response despite of
the fast response time. Controlling the external magnetic field yields a fast but
imprecise response of the fluid. To design for precision a more sophisticated

control of the fluid response is required.

The state of the fluid is defined by the level of organization of the particles in

the fluid. The nonenergized state of the fluid (Figure 1(a)), shows a random

3
orientation and positioning of particles. When energized with a magnetic field,
the MR fluid shows particle organization patterns parallel to the magnetic
field (Figure 1(b)). The particle organization state of the fluid is indicative of the

interparticle forces generated by the magnetic field.

    

No Magnetic Field Magnetic Field
H=0 H>0
\ ‘ -
-I
’I \ Add
‘ I
Q -
- \ ..:..,--~..:-.:-:.:: :2 ‘ . - iizrijli-ifi'
I O.
‘ ’ Magnetic
- Field
(3) (b)
Random Orlentatlon Partlcle Field Induced Orlented Partlcle
Non - Energized State Energlzed State

Figure 1.- Non energized and energized particle orientation and positioning.

The physical properties of the fluid are functions of the organization state of
the fluid, particles and the forces between them. To control the physical
property response of the MR fluid it is necessary to control the state of the fluid
through the applied magnetic field. The particle state of the MR fluid combined
with the applied field governs all physical properties (1). This generates the
non-linear, hysteretic, time-varying characteristic behavior of MR fluids and

makes the relationship of the external field with a given property not unique. To

4
maintain a desired value for a property of the fluid is necessary to control the

particle state of the MR fluid.

%= f (5.14)
y = g(§.u)

(1)

A measurable effect representative of the state of the fluid has to be found.
This effect will be used to implement a particle state sensor. The accurate state
sensor would enable precise response control. The sensing property should
be sensitive to changes in internal particle organization state. Another desired
characteristic of this effect is easy to be easy to implement in real devices.
Sensitivity of three magneto-electric properties: resistance, inductance, and

capacitance will be tested and their suitability will be evaluated.

Magnetorheological effect

The internal organizational state of MR fluids change in response to the
presence of a magnetic field. Particle alignment that takes place under an
applied field is called the magnetorheological effect. The magnetorheological
effect was demonstrated in the view of an optical microscope with a low
concentration (3% est.) MR fluid suspension under a magnetic field applied
from 0 to 40 kAlm. The results of the observations show a change of internal
organization as a function of the applied field and time. Particles are dispersed
and randomly oriented (Figure 2(a)) in a non-energized state. An applied
magnetic field of 6 Wm. produces chaining of particles that show a classical
“worm” pattern (Figure 2(b)). Increasing the field to 12 kA/m produces wider
chains that tend to locate parallel to the magnetic field (Figure 2(b)). separation
between particles and the carrier medium becomes evident. Thin chains totally
aligned to the field (Figure 2(d)) were formed when a 20kA/m field was applied.
Increasing fields produced a movement and breaking apart of chains to form
wider chains called aggregates, alignment was kept and greater areas of pure

carrier medium were shown (Figures 2(e) and 2(f)).

47.

2"

 

(e)H=30kA/m (f)H=40kA/m

Figure 2.- lntemal particle organization of MR Fluid as a function of applied

field.

Sensor Development

The Magnetorheological fluid has an inherent non-linear and time varying
response. The time response for MR fluids has been reported not to exceed
10" sec (Kordonsky,1993), which is considerably faster than the time response
of electromagnetic transient processes in a magnetic system and all hydro-
mechanical processes. Despite the small time constant , to get a precise
response it is necessary to develop a state sensor which could be used to

control the response.

Three properties that react to the external field were considered for
evaluation: Inductance, Capacitance and Resistance. The first property studied
was the Inductance because it would give the possibility of using the same
electric circuit that generates the field, thus avoiding the need for an additional
secondary circuit. Capacitance and resistance of a secondary circuit connected
the MR fluid in series was installed to test their response to changes in applied

field.

The device used to generate the magnetic field for all experiments was a
magnetic core with an MR fluid gap. (Figure 5). The magnetic core was made of
laminated ferromagnetic material and had a reduced cross section at the MR
fluid gap to concentrate the field. The fluid was located in thin wall plastic
reservoirs to perform static fluid measurements. A plastic duct was located
through the gap to carry out measurements with MR fluid flowing. A DC

powered positive displacement pump was used to pump the MR fluid. The

7

8
external magnetic field was produced by applying a DC voltage to the

connectors of the winding.

N tum:

 

 

 

Dc v _._/ if 3: Mn Fluid =

Pump

 

 

 

Magnetic Core

 

(a)

   

(a) (b)
Figure 3.- MR Fluid Device for measurement of (a) static and (b) moving fluid.

The MR fluid used on all the experiments was the VersaFIow MRX - 13500
manufactured by Lord Corporation. The MR fluid was mechanically mixed
before every experiment to ensure homogeneity and to prevent sedimentation,
and magnetic particles of the fluid were also believed to be treated to avoid

settlement.

Inductance Testing

The inductance change on the electric driven circuit as a function of a
change on magnetic field strength has been evaluated. The inductance of a
magnetic circuit is a function of the permeability of the materials that make up
the magnetic circuit, the number of turns of the winding and of the geometric
characteristics of each part of the core. The magnetic circuit comprises every
part of the ferromagnetic core and the MR Fluid gap. Using Ohm’s law for
magnetic circuit a formula for the inductance can be obtained (2). For constant
geometric parameters and number of turns, the inductance is a function of the
permeability only. Ifthe permeability of the MR fluid is sensitive to changes in
particle organization state, a measurable change in inductance would indicate
a change in the state of the fluid, and it could be used to measure the state of

the fluid.

 

L= , <2)

 

The electrical circuit works as a actuator and a sensor at the same time.
The complete circuit includes the winding ( inductance and resistance) and a
known resistance resistor (Figure 4). A DC voltage plus a small AC voltage are

applied to the terminals of the circuit .The measurement method used to

10
measure inductance was the three voltementer method (Electrical Circuits,

Siskind).

 

 

 

 

 

 

 

 

L: R, ~Ez~cosd (3)
ER-Z-it-f
2_ 2_ 2
c050:E E" El (4)
ZEREz

Figure 4.- Three voltmeters method to compute Inductance.

Experimental Setup for Inductance measurements.

The experimental set up used to measure the sensitivity of the inductance

respect to changes on the applied DC field is shown in the figure 7.

 

3
ill

 

5U

 

 

D

 

 

 

’U

i
I

 

 

 

 

 

 

Figure 5.- Experimental setup for inductance measurement.

A LabView program was written to acquire the AC measurements required
to compute inductance. A Wavetek 12 MHz synthesized function generator
Model 23 and a Hewlett - Packard 6825A Bipolar Power Supply — Amplifier were
used to generate the input voltage. Two Hewlett Packard 3478A and one
Keithey 175 Multimeter were used to acquire the voltage measurements. All
instruments were connected to the computer by GPIB connections.

11

Inductance Measurements

Inductance measurements were taken with the gap filled with MR fluid. All
measurements are for steady state given the fast response of the fluid . The
DC voltage was increased from 0 to 20 Volts to generate magnetic DC fields
that ranged from 0 to 128 kA/m . The AC voltage frequency was 100 Hz, and the
amplitude source was kept constant at 0.25 Vpp which represents only 1.25%

of the full scale DC applied field.

Inductance measurements were taken with the gap occupied by the static
MR fluid, the flowing MR fluid and air only (Figure 9). The total measured value
of inductance is dominated by the inductance of the ferromagnetic core itself,
which showed a typical saturation curve. The data revealed a 16.7, 15.0, and
15.6 % decreasing change on inductance for the air gap, static MR fluid gap
and flowing MR fluid respectively over the entire change of magnetic field. The
measurements for low fields regions (0 - 30 kA/m) were stable and repeatable.
The higher field ( >30 kA/m) region produced unstable results. The difference
associated with the fluid state in the core’s gap represented only a 16.7 -

15.6=1.9% change in measured signal.

12

13

 

 

:. .3, -—°—Air Gap
67-00 i "<3 I MR Fluid gap - static
5 22-3: \\ . . MR Fluid gap - flowing
E ' 1. .
: 61.00 R" -_'zr ,, , ..
59.00 + ‘:’ .r "~‘:-\4;-;;;
57.00
55.00 1‘ x 1
0.0 50.0 100.0 150.0
H [kA/m]

Figure 6.- Inductance vs. applied field.

The inductance value for the MR fluid flowing through a duct placed in the
gap at several power inputs also showed a small change (less than 0.25%)
with respect to the static fluid value (Figure 10). The magnetic field was kept at
zero for this experiment. The inductance of the MR fluid as a function of a
magnetic field independent of the inductance of a ferromagnetic or other
material core can be obtained if an MR fluid core is used. A core of this kind
was built and inductance measurements as a function of time for increasing
magnetic fields (0 to 80 kA/m) were taken. Measured data (Figure 11) shows
stable and repeatable values for lower fields ( H<30kA/m) and unstable and
unpredictable values for higher fields (H>30kA/m). The inductance of the MR

fluid only increased 0.83% over a 30kA/m increment on the applied field.

Inductance L [mH]

14

68.70 *
68.68
68.66
68.64
‘58-‘52 0.25% Change
68.60
68.58
68.56
68.54
68.52
68.50 A
68_48 . 1‘ l ‘41 l l
0.00 5.00 10.00 15.00 20.00 25.00

Power on the pump [VA]

 

 

Figure 7.- Inductance vs. MR fluid flow.

 

Figure 8.- MR fluid core inductor.

   

5.15 1 ”Magnetic Field strength H l kA/m] 80
‘ —0—|nductance L [mH] - .

5.1 l 70
15051 ° .I 60 E
E ‘ . . I. , . E E

] - O
J 54' X . '3’» 51.50 E:
g l .1 ' ‘ . 40 .g 3:
g 4.95 1 Stable Region > “é 1:
o I . I: 30 “a
3 ‘ 5 t:
g 4.9 " E 2
.. .u I 0.. ~ 2 0 a
e, e e :
4.85 f..’.\ 9'....‘ .'..‘. O. .. 1 0
j 0. ’~
4.8 . ' 0
0 Lo :3 l0 o in o in
1- m V (O N a) o
time [s]

Figure 9.- MR fluid core Inductance vs. time

Capacitance Testing
The steady state capacitance change of a secondary circuit as a function of
the magnetic field strength was evaluated. The capacitance values for a
parallel plates capacitor is a function of the area of the conductors, the distance
between them and the perrnitivity of the material filling that space. Capacitance

changes for constant geometry are functions of the perrnitivity of the material

16

only (3). Under a magnetic field the particle organization on the MR fluid

changes.

 

d (3)

MR Fluid

   
 
    
   
    
   

j  Isolation

Plates " "5::;::‘,33.;}£:f;

  

Sensor Circuit

e(t)

AC Volta e
V 9

DC Voltage Actuator Circuit

Figure 10.- Experimental setup for Capacitance and Resistance

measurements.

Resistance Testing
Resistance change of an MR fluid resistor as a function of a magnetic field
was evaluated with two parallel conductor plates inside the MR fluid gap. The
plates and MR fluid formed a parallel plate resistor. The resistance value of
such a resistor is a function of the area of the plates, the distance between

plates and the resistivity of the material ( MR fluid) between the plates (8).

17

R=po% (8)

If the pennitivity and/or resistivity of the MR fluid are sensitive to the internal
organization of the particles, then a measure of the change of capacitance
and/or resistance would reflect a change in the state of the fluid, and therefor

capacitance and/or resistance could be used as a state sensor.

Experimental setup for Capacitance and Resistance Testing

Two circuits (Figure 10) were used to perform these measurements: the
actuator circuit and the sensor circuit. The actuator circuit was connected to
Hewlet Packard 6267B power supply to produce DC actuation fields. A
Wavetek function generator model 23 and a Hewlet Packard 6825A power
supply / amplifier were used to generate AC actuation fields. The sensor circuit
connected two parallel plates located in the MR fluid with a constant separation
between them. Good contact between plates and the MR fluid was assured at
all times. The sensor circuit was connected to a Fluke 6063A RCL meter and
was used to measure series and parallel equivalent capacitance and

resistance.

18

Secondary circuit

 

Figure 11.- Equipment setup for MR fluid capacitance measurements.

Capacitance measurements

5.3 T 0 measured value for plates :3

W I measured value for wires
4-8 Plates linear regresion; r=0.9851
wires linear regresion; r=0.9852 ’

 

 

4.3 ‘“
3.8
3.3 “”
2.8 ‘“

 

2.3 it

1

MR Fluid Capacitance [ pF]

 

 

 

Magnetic Field Density [ K Gauss]
Figure 12.- Parallel equivalent capacitance as a function of applied field.

Measurements were taken with the plates inside the MR pool. The plates
were positioned parallel and also perpendicular to the field lines. Plates of

20mm and wires 28 AWG were also tested. The parallel equivalent

19
capacitance measurements (Figure 19 ), showed an increment of 44.4% and
113% for a total increment of 340kA/m on the applied field for the wires and
plates respectively. A correlation factor of 0.9852 and 0.9851 for a linear
regression analysis belong to the two corresponding sets of data although the
plates data show a saturation curve trend. Series equivalent capacitance
measurements (Figure 20 ) showed no change for the wires capacitor and a
28.2% increment for the plates capacitor. Linear regression on these show

0.030 and 0.9620 correlation factors respectively.

 

 

 

 

 

n—a 1 ,¢ ——-———
g 5.5 i
i l
g
89 5 i
_:_l + 0 Measured, plates values
IL 4,5 I Measured, wire values
g + “ ~ Plates, linear regresion; r=0.9620
‘ -—— Wires, linear regresion; r=-0.030
4 if 4 ——«—+ l 1 ———-~ —«- -—»— —-+
0 1 2 3 4 5

Magnetic Field Density [ K Gauss]

Figure 13.- Series equivalent capacitance as a function of applied field.

Resistance measurements

Parallel equivalent resistance measurements for the MR resistor with the

plates placed parallel to the magnetic field ( Figure 21), showed a 1.4% decline

for the wire resistor and a 44.1% decrease for the plate resistor over a 340

kA/m increment on the applied magnetic field. Correlation factors of 0.3811 and

0.9933 were computed for the linear regression of both sets of data

respectively.

80
75

__. 70

E

O 65

E

8

C

a

E

O

O

r:

2

2

II.

c 40

E
35

60 4
55 +
50 '

45 ‘*

 

‘1'

 

     

+

0 measured value for wires

I measured value for plates

wires, linear regresion; r=-0.030

plates, linear regresioE r=0.9620
i T

 

 

l . —

1 2 3 4 5
Magnetic Field Density [ K Gauss]

Figure 14.- Parallel equivalent Resistance as a function of applied field.

Series equivalent resistance measurements ( Figure 22) showed a 17.2%

decrease for the wires resistor and a 40.5% decrease for the plate resistor

over a 340 kA/m increment on the applied field. Correlation factors of 0.9950

20

21

and 0.9917 were computed for the linear regression of both sets of data

 

 

 

respectively.
60 L ....... _

.. '1' 'I III a...
a i- r
O 50 ’
E
H 40
8
C
E, 30
8
g 20 + 9 Measured, plates values
a I Measured, wires values
a: 10 ”5 Plates, linear regresion; r=-0.9917
: Wires, linear regresion; r=-0.9950

0 -2 fi1 a —1———~—» -——+ — __ ~4‘

O 1 2 3 4 5
Magnetic Field Density [ kGauss]

Figure 15.- Series equivalent resistance as a function of applied field.

Resistance measurements with the plates placed parallel to the field
showed no change under a 340 kA/m increment on the applied field in either
parallel or series equivalent circuits. Capacitance with the plates placed
parallel to the field showed no change for a parallel equivalent measurement
and showed a 2.8% increment over a 340 Win change on the applied field for
a series equivalent measurement. These measurements demonstrate the
ability to measure the directional orientation of field induced internal structure

and hence the directionality of the internal organization state of MR fluids.

22
AC fields were applied to measure resistance and capacitance of an MR
fluid. Under a low frequency AC field, a changing MR effect was observed.
during an field change at approximately 0.1 Hz., no MR effect was observed for
zero field value of while maximum MR effect occurred at maximum wave
amplitude. Change in field sign produced a fluid motion perceptible when
holding the field probe. High AC field frequencies caused immediate

unchaining independent of AC field amplitude.

Sensitivity of Inductance, Resistance and Capacitance

Sensitivity of these three measured electric properties as a function of the
applied field was investigated. Sensitivity was computed as the ratio of the total
increment of every one of these properties over its average value to the total

increment on applied field over its average value (11).

 

SQ = (Q2 —Ql).(H2+H1)
H (H2"H|).(Q2+Q1)

(11)
Computed sensitivity for inductance measurements showed the lowest

sensitivity to applied field, 0.0041 (Table 1). The MR fluid resistance connected

in series showed a sensitivity of -0.2542. The sensitivity of the capacitance to

applied field was the highest, 0.3611. The highest correlation factor for a linear

regression analysis of all sets of data belongs to the resistance.

Permeability, perrnitivity and resistivity are the material properties which

changes are been sensed by the inductance, resistance and capacitance

23
respectively. It is important to state that the changing properties are the material
properties which are a function of the particle state organization. The computed

relative permeability increased from 31.5 to 31.76. The resistivity decreased

from 148 to 88 K!) m. The relative perrnitivity increased from 65 to 138.5.

Table 1.- Sensitivity of magnetic and electric properties.

 

Property Range Applied Sensitivity Correlation
Field factor for
“near

H I kAIm I regression

Inductance I mH l 4.84 - 4.88

 

 

 

 

0 - 30 0.0041 .9531
Relative Permeability 31.5 - 31.76
Resistance [M a ] 37 - 22
0 - 340 -0.2542 .9917
Resistivity [Kn . m] 0.148 - 0.088
Capacitance [p F] 2.3 - 4.9
0 - 340 0.3611 .09851

 

 

 

 

 

 

Relative Perrnitivity 65.0 - 138.5

 

Conclusions and Recommendations

Sensitivity of inductance, resistance and capacitance of a VersaFlow MRX -
153CD MR fluid to changes in magnetic field was investigated in order to

determine their suitability for use as an MR fluid state sensor. Changes on

24
inductance, resistance and capacitance showed actually changes in
permeability, resistivity and perrnitivity. Sensitivity values of these properties
were obtained for fields up to 340 kA/m. The Inductance of the MR fluid core
under magnetic fields in the range of 0 - 30 kA/m showed a very low sensitivity
0.0041. Unstable and unpredictable inductance values were obtained for
higher fields. Resistance sensitivity was of -0.2542. Capacitance showed
highest sensitivity of 0.3611. The applied field ranged from 0 to 340 kA/m for

capacitance and resistance measurements.

Inductive sensing is not attractive because inductance change has a small
sensitivity to both internal particle organization and low applied fields. Under
higher fields unstable measurements were obtained. Real MR fluid devices
will have always an electromagnetic circuit with a very small MR fluid gap.
Because of this geometry, the total inductance measured will be dominated by
the inductance of the non-MR fluid portion of the electromagnetic circuit, eg. the
ferromagnetic core, making changes in MR fluid permeability even more

difficult to detect.

Resistance and capacitance sensor circuits are highly sensitive to both
applied magnetic field and particle organization, and provide an accurate
measure of MR fluid internal state. Parallel conductor plates placed normal to
field lines gave the most predictable signal and highest sensitivity.
Resistance and capacitance sesors have is a big advantage over traditional

shear rate sensing used to compute viscosity where fluid movement is

25
required because they provide accurate measures of particle organization state

for both static and moving fluid.

APPENDIX

Inductance Measurement LabView Program

 

 

Desired Values of

Inductance [mH] f urrent Inductance [mH]|

 
     
   
 

 

 

 

 

 

 

 

DC Field]

1 5.0- if:

 

 

10.0"

5.0-

 

 

 

Figure 16.- Front Panel. LabView Inductance measurement program.

_, _ , 010.21
- initialize the Output

 

 

 

 

 

Figure 17.- First Frame. LabView Inductance measurement program.

26

III-IIl-II-I-Illllnm:lllllllllllll‘llII

   
  
   
     
    

  
    
   
 

 

   

Teta=acos((E’\2-EzAZ-ErAZ)
/(2'Ez'Er));

L=((Ez'R'sin(Teta))/
(2'3.141592'f‘Er));

 

 

 

 

 

Current Inductance mH

‘qu

EEl

Hal-l
BL Mina
IDesired Values of Inductance [mHI

 

 

Figure 18.- Second Frame. LabView Inductance measurement program.

 

Figure 19.- Third Frame. LabView Inductance measurement program.

27

Inductance response to a square wave field excitation

Inductance measurements for a static MR fluid under the excitation of a
square wave input field were obtained. Low and high value fields were of 0 and
60 kA/m. The inductance response to the low field showed (Figure 21) a stable
pattern, although the value for zero field increased for each cycle. The high field

inductance measurements showed no trend, and had large variation between

them.

 

 

  

 

 

 

5.4 -— -I—H=0 kA/m

5' 5.3 --

E. 5-2 +H=60
.l kA/m
O

0

c

3

0

3

'U

E

5.0 10.0 15.0

 

Time [s]

Figure 21.- MR fluid response to a magnetic field square wave

28

Relative properties change as a function of applied field.

 

 

120.0 T
100.0 i Relative Permmvity/X/
r... .
g- 60.0 T '
a FtelatIVe / I
"53 40.0 * permeability .2
a: 20.0 “i
E I ,,.§?51/
g 0.0 say/.21.---“
: -20.0 i “I 333333333 Bfigismiw
a 1-.-..._.--.-._._- -22 - 2.--.
5 -40.0 I W“-
a! .50.0 % % I IL 5}
0 1 2 3 4 5

Magnetic Field Density [ k gauss]

Figure 21.- Relative properties change as a function of applied field.

29

BIBLIOGRAPHY

BIBLIOGRAPHY

Winslow, W. M. 1947, Translating Electrical Impulses into Mechanical Force,
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Shulman Z P., and Kordonsky V. l., 1982, Magnetorheological Effect ,Nauka l
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30

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31

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