A HEW METHOD FOE THE VISUALIZATION AND
MEASUREMENT OF ULTRASONIC FIELDS

w
Grant S. Bennett

A THESIS
Submitted to the school of Graduate Studies of Michigan
State College of Agriculture and Applied science
in partial fulfillment of the requirements
for the degree of
DOCTOR OF PHILOSOPRY

Department of physios and Astronomy
1952

ProQuest Number: 10008458

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for tho degree of
B O C m OF mUHXXVZ

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Existing Bothods of obsesviBf ultrasonic w o field* ere
discussed sad the liAiiattoas of each pointed oat# together
eltfc «B indication of shy such acestmMeats ere of interest*
A not *ethod i« described efeiefe nee* starch coated plates In
d dilate OQttooao eolation of iodine in * auiscr analogous to
the nee of photograph io ocmAoiooo for tho observation of eleetre~
Magnetic w w

fields* tho process depends on tho acceleration

of tho »t*reh~i©dln© reaction under the action of ulfcrageniee*
oiid evidence is pat forth to sagged that the nsebealsa of the
acceleration it & transport phssnoseenon. Applications of tho
boo toohsl^o ore indicated by several neswrHfteld diffraction
patterns of circular sources at different frequencies end.
distances, by

m

edge diffraction pattern* and by a sound shadow

picture of a load plate* Properties of tho starch •eaaulsioii*
are described by a typical i and 8 curve a® it done photographically*
fee existing techniques - tho mee of phosphors, and the Fohlnan

coll « are exanined in detail* cad it it sheen that the starch
plat# Method is such store flexible and einple to use* end
produces good quality pictures*

!Ehe author wishes to acknowledge his Indebtedness
end express his appreciation to Dr. e .a . Hledemann who
came as head of the Physios Department while this work
was in progress, and who has made many suggestions, part­
icularly with respect to the literature, supplying from
his own voluminous collection many reprints of papers
otherwise difficult of accessj to Dr. T.H. Osgood, head
of the department when this work was originally under­
taken, for encouragement! to Dr. C.D. Hause and Dr. R.D.
Spence for their continued interest, many helpful
discuss ions, and the original inspiration for this
particular field of investigation.

table

of

contents

INTRODUCTION

1

Optical Methods

5

Other Methods

5

THE STARCH PLATE TECHNIQUE
Apparatus

12

Preparation of plates

14

Preparation of solution

IS

General Discussion of Technique

16

Discussion of Resulte

1?

THE PHOSPHOR TECHNIQUE
Experimental Arrangement

21

Disepssiom of Results

25

THE POHLMAN IMAGE-CONVERTER CELL
Experimental Arrangement

24

Discuse Ion of Results

26

CONCLUSIONS

27

A New Method for the Visualisation and
Measurement of Ultrasonic Fields

INTRODUCTION
one of the important applications of ultrasonics lies
in their use for the Investigation of wave behavior on a
laboratory seals, made possible by the short wave lengths
attainable. This seme feature of extremely short wave
length, however, introduces problems in measuring techniques.
For example, in the range of audible frequencies microphones
are used to detect and measure sound characteristics, and
tdie usual rule of thumb is that the detecting device should
be of dimensions less than one-tenth the wave length in
order that the measuring device should not by its presence
distort and destroy the very effect to be measured. Quite
obviously at wave lengths of a millimeter or less, as will
be attained with sound frequencies in the megacycle range
produced in water, such detecting devices are ruled out
by sheer size considerations. Even apart from these diff­
raction effects, for detailed studies of field patterns
it is apparent that an instrument large compared with the
wave length would not be suitable, since the microphone
signal is determined by the average of the measured sound
characteristic over the sensitive area. Further, such a
technique gives values for points, and a point-by-point

plot Is necessary for tho determination of the complete
field* Keck, Heller and Williams (19) have developed a
method in which a pulsed source is rotated about its axis
and the signal produced by a stationary microphone is
displayed on a cathode ray oscilloscope, giving the
directivity pattern of the source. The method is specialised
to this one type of measurement, obviously, such consider­
ations as indicated above have lead to the development of
different techniques for the observation of ultrasonic
fields, taking advantage of effects peculiar to the high
frequency range. In general, these methods give a picture
of the entire field, in much the same sense that a photo­
graphic plate gives a picture of the electromagnetic wave
field, in which relative magnitudes are discernible readily,
and absolute magnitudes are usually somewhat difficult to
obtain, gome of these methods will be discussed below,
classified as to the effect ©f the ultrasonic wave utilized,
and particular attention will be given to the limitations
of each. The latter part of the paper will describe a new
method for such observations which avoids many of these
difficulties, and which la applicable for the visualization
of ultrasonic fields In liquids - in particular, water or
aqueous solutions •

3*
Optical Methods
Optical methods for the observation of ultrasonic
fields have been very extensively developed, one advantage
being that tke measuring instrument * a llgkt ray - meet
certainly will kave ao perturbing Influence oa tke sound
wave* H I optical metkods depend for tkeir operation on
tke ekaages In tke index of refraction of tke medium resulting
from tke variations of density in tke sound wave. Perhaps
tke simplest of tke metkods is tke spark shadowgraph
arrangement, in which light from a short duration spark is
rendered parallel and passes transversely through tke sound
wave* The llgkt is deviated from tke regions of low index,
and there results what appears to be an instantaneous shadow
picture of the ultrasonic wave* Hubbard, Zartmsaa and
Larkin (18) kave used this technique to study diffraction
in air, and it is also applicable t© liquids* One of the
experimental difficulties lies In the production of a suff­
iciently Intense, sufficiently short duration spark source *
Tke class of optical methods known generally as scklierea
techniques is subject to many variations experimentally,
but depends on tke fact tkat the periodic variations of
index of refraction in tke sound wave constitute a phase
grating, and tke light in tke diffraction orders is a function
of tke diffractor. For example, in tke case of a simple,
thin grating tke light in tke nth order represents tke

4*
grating characteristics in a manner peculiar to it* and diff­
erently than the other orders* such that if the diffracted
light be allowed to recombine* one obtains an image of
the diffraetor# The sound ware is not a thin grating* and
furthermore it is mowing* so that the simple theory does
not apply) still it is represented by the diffracted light*
Hiedem&an and coworkers (IS* 16, 17* 24) and at about the
same time Blr (1) have investigated and developed this
type of measurement extensively* using a Variety of techniques*
The zeroth order may be blocked out* the zeroth order only
may be used to form an image* single orders may be used to
view the field, or various combinations of orders, each arr­
angement resulting in a slightly different aspect of the
sound field# liedemaaa* s "method of Isoehrornate" utilizes
white light and a single order to produce a colored image
of the field in which areas of the same color correspond to
areas of constant amplitude* hence the name# the Maoh-gehnder
interferometer is used for the observation of shock waves*
and has been used by Timbrell (30) for the absolute meas­
urement of pressure in a plane wave* but seems less well
adapted to the visualization of the complete sound field#
These optical effects can be classified in terms of the
acoustical quantity operative - the interferometer measures
pres stare directly* the achllerea method responds to
pressure gradient* and the shadowgraph depends on the

5.
second space derivative of pressure*
All the above methods suffer from a oommoa disadvantagenamely, the light traverses the cell la a direction transverse
to the direction of the sound nave, end the region of
optical effect is one of considerable depth* Hence if the
sound field is not completely uniform laterally there is
serious question as to just what the image represents* Since
the usual ease corresponds approximately to axial symmetry,
these techniques can be only indicative of the field
pattern* Hiedemann and Qaterhammel (16, 17, 24) have avoided
v*kick
this situation by use 6f a quarts source/Ms long and
narrow, corresponding to a slit source, the field of which
was observed by means off light travelling parallel to the
long dimension of the quartz bar* Ihe same technique could,
of course, be applied to the other methods, but they do
not represent general procedures for obtaining field
patterns* schaafs (29) has used the schlieren method for
observation of the vibration of crystals, sending the light
through the quartz in the direction of the sound wave, but
the same lack off homogeneity off index variation in the
direction of light travel renders this technique difficult
of interpretation In terms of the sound field*
Other Methods
optically, diffraction patterns are obtained as the
transverse section of the beam, rather than as longitudinal

6.
sections* For tfels reason, as well as tke desirability of
of examination of shadows cast by obstacles, one is lead
to seek methods for observing tke transverse section of tke
sound field* Ultrasonic waves have long been known to
exhibit certain effects peculiar to tke high frequency range

as well as tke phenomena of audible sound* Among these are
h dynamical 1 or Rayleigh disk effect, tke acceleration
or Initiation of certain chemical reactions, thermal effects
resulting from tke high intensities readily attainable at
high frequencies or from tke absorption of short wave length
sound, and certain other effects whose origins are difficult
to catalogue* All of these types of effect kave been used
to iadloat© ultrasonic wave field distributions*
Ike Rayleigh disk effect, long used for tke absolute
measurement of sound intensities, is manifest as tke prop*
erty of a small, flat disk to align itself normal tk the
direction of the sound wave* Poklraaa (26, 27, 28} has taken
advantage of this property ia his image converter cell, a
thin circular cell having a back of thin metal, a front of
glass, and containing a suspension of fine aluminum flakes
in xylene* 33»e cell is Illuminated fro* the front, and
because of the random orientation of tke Al flakes tke light
la reflected diffusely. If, now, a sound wav© eaters tke
cell through the thin metal back, the flakes in the field

7*
are oriented aomal to tke direction of sound travel,
and specular reflection takes place* Tke sound field Is
tkus made visible# and tke pattern appearing la tke cell
can be photographed. This method will be discussed, in more
detail below, as It la one of the techniques scrutinised In
this work*
Marlnesco. observing that the light sensitive Eder
reaction was equally well initiated by ultrasonic waves took
the logical step of studying the action of ultrasonics on
photographic plates, and found that a latent, developable
image was produced* Ernat (9) and Bennett (2) have applied
this phenomenon to the observation of sound fields, Ernst
using the longitudinal section and Bennett the transverse
section* The basic causes for the ultrasonic linage production
are not yet completely understood* Pinoir and Pouradler

(26)

are of the opinion that the exposure is due to the luminescence
of bubbles of dissolved gas, although this opinion is not
universally held* Marineseo originally attributed the effect
to the aVtivatioa of the silver atoms by collision. This
method requires sound waves of relatively high intensity,
and long exposure times - of the order of an hour - are
necessary* Further, the customary photographic A must be
observed. The long exposure to the sound beam produces
thermal effects in the gelatin, in some cases resulting in
an actual melting, and in the writer’s opinion having to
do with the formation of tke image.

So
schreiber and Degner (30) and almost simultaneously
Eekardt aad Lindig (B) kave used phosphors for tke visualization
of tke ultrasonic wave, Ike teeknlque Is essentially identical
with tkat of Infra-red pkospkors - tke phosphor ( e.g* znS
with Cu as activator) is excited with ultraviolet llgkt and
after a ekort decay period is subjected to tke ultrasonic
beam# $ke acoustic energy absorbed by tke pkospkor and

s

supporting film appears as keat and accelerates tke phosph­
orescent decay* so tkat the areas upon which tke sound Is
Incident appear bright against a less brilliant ground. If,
now* tke sound be turned off before tke decay is complete*
tke previously bright areas appear darker than their surroundings
as a result of the "unloading" of tke stored-up energy, fhe
patterns may be photographed in tke conventional manner* or
a contact "print** may be made on a piece of cut film applied
directly against the pkospkor. fkis method will also be discussed
in more detail below. Ernst and Hoffmann (10) kave reported
tke use of various thermally sensitive substances for tke
observation of sound fields* For example* they kave used
pigments which change color at a given temperature* etc* as
well as phosphors. Most of tke changes are apparently rev­
ersible* so tkat photography is necessary to obtain a permanent
record* Dognorn and Siraonot (5* 6* 7) kave investigated
thermal effects* although none of their results appear to
be directly applicable to the present problem*
Many direct chemical effects of ultrasonic waves have

9.
long been known ( see Bergman** ref . 3* chap, V ) and there
has bee* continued interest in the underlying principles
of euek action* Typical reactions are the production of
free Iodine from KI, the liberation of Olg from aqueous
solutions of CGlg* the formation of MttOg from KlteO^, etc.
in every ease the effect is as If the ultrasonic nave were
an oxidising agent. Investigators agree that intensities
of eavitatlon magnitudes are required, and the reactions
take place only when certain gases are present In solution*
ft. Kliag and R • Kllng {20) have shown the presence of
hydrogen peroxide in previously pure, oxygen saturated
water after ultrasonic Irradiation, and evidence of © zone*
If air be the dissolved gas rather than oxygen, on© obtains
oxygen~eontainlng compounds of nitrogen, Grabar and
prudhonmte have reported (12) similar researches with
similar results, weissler, Cooper and Snyder (33) have
investigated the liberation from KX of free iodine in a
solution containing CCl4, and conclude that the liberated
I is primarily an indicator of the free chlorine produced.
Frenkel (11) has proposed a theory for the chemical action
of ultrasonic waves based on the electric charge that may
result when a bubble is formed due to the statistical
fluctuations In the distribution of ions. He concludes
that a sufficiently strong electric field may be produced
in the bubble to result in a discharge through the vapor,
producing active radio sis either directly, or indirectly

10.
through the action of the light accompanying the discharge .
The difference in behavior of different dissolved gases
results* then* from the differences la vapor pressure and
and electrical properties of the Vapor in the bubble#
Bresler (4) has reported experiments which he feels confirm
completely the theohy of Frenkel. Griffing (IS) on the
other hand* has proponed a theory for the chemical action
predicated on the very high temperatures possible in the
bubble# These temperatures, possibly of the order of several
hundred degrees Centigrade, give rise to large thermal
gradients in the liquid in the immediate vicinity of the
bubble, thereby producing the chemical reaction. According
to this theory the action depends on the thermodynamical
properties of the gas, the temperature being determined by
the ratio of the specific heats through the term (j'-l)
and the thermal gradient in the liquid depending on the
thermal conductivity of the Vapor, weissler (32) has pointed
out, however, that certain effects are not explained by
this theory, end suggests that the rate of collapse of the
bubbles has some influence. To the writer* s knowledge, such
direct, irreversible chemical changes have not been applied
for the observation of ultrasonic field patterns, although
the liberation of free iodine sounds interesting because
of its positive effect on starch. Haul, Studt and Rust(14)
have used a plate carrying a grid in which was imbedded

3*3**
starch for the measurement of tke quantity bf iodine
liberated, and kave investigated tke aetion in various
solutions*
m

ultrasonic wave of less tkan cavitation intensity

may influence tke rate, of reaction, as kas keen known for
tke stareh-lodlne reaction, wklck is accelerated in tke
presence of tke sound ware* This effect immediately suggested
Itself in tke search for an acoustic analogue to tke photograpkio process, and it is witk tke tecknlques and results
of tke development of suck an analogy using tke etarchiodine reaction tkat tkls report will be concerned* Comp­
arisons will be made witk other methods, specifically tke
Pohlraan ©{tell and tke phosphor technique, from tke stand­
point of ease of obtaining results, possibilities, and
quality of records* the technique to be described will be
shown to be muck simpler and flexible in manipulation tkan
either of tke methods mentioned, and to result in pictures
as good as or better than the phosphor technique at some­
what lower sound intensities* Tke near-field, or Fresael,
diffraction patterns of transducers will be used as a basis
of comparison, and certain other applications will be
indicated*

12 •
TH& STAKCH

PLa TK

TECHNIQUE

Barium titanate ceramic disks were used for this work.
Thee® transducers are commercially available in several
frequencies and sices with electrodes and leads attacked.
This type of transducer is of low electrical impedancef kas
a ratker broad resonance* and tke electromechanical coupling
factor is higher tkan for most piezoelectric materials. For
these reasons tke ceramic transducer is somewhat simpler to
handle elreultwice* and makes available higher acoustic
intensities than a quarts source operated from the same
circuit. Tke transducer was driven by a crystal controlled
oscillator using a type 804 pentode tube. Tke nominal
output power of this circuit Is about 50 watts. An assortment
of control crystals and tank ©oils makes available frequencies
in tke range 0.5 - 9 megacycles per second. Tke circuit
diagram is shown in Fig. 1. Tke transducer proper is coupled
to tke tank circuit of the oscillator by means of a link
coupling and appropriate matching circuit. A high impedance
transducer suck as quartz must be connected in parallel
with a resonant circuit terminating the link* while tke
barium tltanate requires only a parallel capacitance in
place of tke second tuned circuit. Tke very high Q, of quartz
requires a very careful match between control crystal and
transducer with respect to resonant frequencies* while tke

Fig. I
OSCILLATOR

CIRCUIT

8 04

3

RFC

. 0 2 5 yuf d

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2
J 2f1n/h
□

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XTAL
15 K

2w

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7.5 v
+3 0 0 v +4 5 v

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2.5 v CT

5/25h

866

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250 v

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13*
resonance curve for tke titanat© ceramic la sufficiently
br§$d tkat tkls Careful matek is act required* ceramics
used kere sere of nominal frequencies 19 2.5, and 5 mcy/seo*
and sere driven at 1*073* 2.390* and 4.970 mcy/aec, resp­
ectively* representing tke frequencies of control crystals
closest to tke nominal transducer frequencies.
*■

Since tM© work was to be done in water* and since It
is desirable to bav© as muck of tke acoustic energy as
possible in a single beam* tke transducers were mounted so
tkat one face was in contact wltk tke water* and tke otker
wltk air. Because tke acoustic Impedance of tke water Is
muck closer to tkat of barium tltan&t© tkan Is tke case
for air* by far tke greatest part of tke energy goes into
tke liquid. Pig. 2 skows tke details of tke transducer
mounting. Ike transducer disk proper was cemented into tke
recess provided wltk ampfeeaol liquid polystyrene coil dope*
which* of tke various methods tried* proved to be simple
and satisfactory. Ike brass shell and the water serve as
tke ground connection* and the high potential lead Is brought
in to the rear face of the disk through the stem, which is
sealed with red wax or otker material.
Ike transducer unit was mounted in a holder as shown
la Fig. 3* which also provided a holder for the plate which
be

could continuously/'for distances from less than one centimeter
to about 40 centimeter® from the transducer. Ike complete

Fig. 2

TRANSDUCER ASSEMBLY

i--- 1--- cm.

14*
mounting was adjusted outside, then lamersed in a tank
containing about five gallons of water for the exposure. 1
Preparation of Plates
In the first attempts to stake starok plates it was
thought necessary or desirable to provide a carrier for tie
starok. For this reason a gelatin solution was prepared,
to wkich was added ike dissolved starck. Many different
combinations of proportions were tried, wltk no particular
differences in results. Shortly it was found that the
gelatin was not necessary, the cooked starok forming a
satisfactory *emulsion* itself. As a matter of fact the
gelatin showed a strong tendency to dry out hard and brittle,
cracking and peeling off the glass plate, The starch originally
used was reagent grade, obtained from tk© Chemistry Depart­
ment, and mad© very satisfactory plates. This particular
bottle was exhausted, and the next starck obtained, although
meeting the same general specifications, was found to be
unsatisfactory, in almost every case the starck layer did
not adhere to the glass, and cracked. Many varieties of
starches were tried - reagent grade, corn starck, household
laundry starck, commercial laundry starch having a fat
additive for smoothness, and household liquid starch * and
none formed a satisfactory plate. The liquid starch did not
crack on drying, but formed large grains. The final mixture
adopted uses a little of the liquid starch together with

15.
til© cooked atarok to take advantage of the preservative
lit the liquid starch# ©ad tke combination produces very
satisfactory plates* It was found that if tke starck mixture
were irradiated witk ultrasonics before heating the entrained
air was driven out, and the starch more finely dispersed#
resulting in smooth, uniform plates*
While there seems to be nothing critical about the kind
of starch, proportions# or treatment# current practice is
as followss 1© g' of Starch (dry) is mixed into 200ml of
water to which is added 10ml of liquid starch; the mixture
is irradiated with 5 mey/sec* ultrasonics for about four
minutes# after which the mixture is heated over hot water
to 7S°C; the hot solution is poured onto clean glass plates
and allowed to cool# after which the plates are ready for
use* Lantern slide cover glass plates were used# and of
course they must be kept level until the starch has hardened*
preoaratjoa of Solution
A stock solution of iodine was prepared by dissolving
3Qg* of iodine crystals in methyl alcohol to make one liter#
and appropriate amounts of this solution added to the five
gallons of water normally used in the tank* For most of
the work reported 100ml of iodine solution^ although again
the amount is not critical* lift© more iodine in the tank#
the more the plate as a whole darkens • Except for the extreme
Case where the whole plate darkens completely# there seems

Id.
to be little variation 1a contrast with the quantity of
Iodine used*

general Discuss ion of Technique
Th® mounting shown la Fig* 3 was designed to facilitate
pictures of tke transverse seetion of th© sound field. In
typical operation tke whole mounting was removed from tke
tank, tke necessary adjustments made, tke plate Inserted
in tke plate bolder, and tke complete system replaced in
tke tank. Tke transducer is energised for tke proper lengtk
©f time «* usually of tke order of one to three minutes *
the mounting removed and the plate extracted* Tke only
treatment of tke plate required Is that it be washed off
and allowed to dry*
Plates mad® and exposed In tke manner described show
a tendency to fade in time* It has not been possible to
correlate tke time of fading with any other variable, although
on tke whole tke more Intense tke darkening tke longer
tke plate lasts* In general tke plates are usable for a
matter of weeks after exposure, although some lightly
exposed plates have faded in a day* For most purposes the
time Is sufficient, but a truly permanent record can be
easily made by contact printing onto photographic paper*
Since tke starch plates show somewhat less contrast than
photographic emulsions, it is frequently desirable to use

17*
#4 or #8 paper for the prints. These first prints east
then he used la ttkra for second prints, which are then
positives with respect to the original plate# of course, a
certain ©mount of detail is lost la the reproduction
process, so that quantitative measurements should toe made
on the starch plate# Fig# 4 shows the three types of
record photographed together# it should toe pointed out
that the loss of detail in the second print is usually
not as sever® as indicated her® * in this case the copy
work was don© to torlag out detail in the original plate*
Succeeding figures show positive prints of the sound field
under various condition®, with pertinent information
given for each* Fig 6d is the second print used for the
photograph of Fig* 4*
Discussion of Results
The photosensitive properties of photographic emulsions
are described toy Bur ter and Driffield curves, in which
the density is plotted as a function of the logarithm of
the exposure# Exposure is defined as the product of light
intensity and exposure time, and density Is defined as the
logarithm of the ratio of the incident light intensity to
the light intensity transmitted toy the emulsion* In. each
case the logarithm to the base ten is used# The resulting
typically sigmoidal curve® indicate the rang© of exposure

STARCH

PLATE

and

PRINTS

18.
for the emulsion by the position of the steeply ascending
portion^ and the slope of the approximatelyOgives the
contrast index, op ttgamma* * Mariaesco aad coworkers used
a large aperture densitometer in their work with photographic
emulsions ia the souad field, and showed that the average
densities so obtained exhibited the same general relationship to ultrasonic exposure as to light exposure when a
dilute solution of developer was used as the sound trans­
mission raediufi la which the plate was immersed. They even
observed the phenomenon of reversal, or solarizatioa, for
very long exposures*
It seemed obvious, then, to investigate the character­
istics of the starch plates in the same fashion. In the
absence of precis© information as to the sound intensities
the exposure was taken as the product of transducer current
and exposure time. Under similar conditions of position
and transducer current plates were exposed for varying
times, and the density of each read on the Ansco-Sweet densi­
tometer at some convenient common position, usually the
central dark spot. In each case ant average or typical back­
ground density was determined and subtracted from the value
for the point in quostiom. Such readings wer© mad© on
plates of different batches, on th© same plates over an
extended time to determine the effect of fading, for
different transducers, and for different transducer currents.
While the position of the curves along the abolssa varied

19*
for each set of conditions because the sound intensities
were not known quantitatively, all curves showed about the
same shape, and all gar© a gamma of about two. Mo curve was
carried so far as to show the shoulder, since the starch
"emulsion* showed a tendency to break up ■under prolonged
exposure. On© would certainly expect a saturation effect
to exist, and perhaps if higher intensities were available,
allowing of a large exposure at short times, this part of
the curve could be shown. Fig* 8 gives a typical curve for
starch plates.
Figs. 6a-6h show a variety of near-field or Fresnel
diffraction patterns for different transducers and frequencies.
It is not to be expected that these patterns be interpretable
la terms of a piston source, since no attempt was made in
the design of the transducer shell to obtain such behavior.
The patterns do, however, look Ilk® what might be expected
for a circular source. It should be noted that these figures
represent fields much closer to the source than are possible
optically - In certain cases the pictures were made at
distances of 6-7 wave lengths • The theory of such very near
field patterns is currently of interest, and such pictures
as shown here should be of assistance in verifying such
calculations*

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20*
Beeaua* of the email diameter of the main beams
produced by the sources meed the observable* of such
phenomena as diffraction by obstaeles a*d apertures Is
somewhat difficult. Fl<« ? shows a* edge diffraction
patter*! where a lead plate about 2am. thick served as
the diffraster. FIs* 8 shows the Imago of a similar lead
plate with holes of differemt diameters drilled 1* it. To
avoid both the noar~field dlffrastlo* a*d dlffrastlo* at
the holes, a*d beoause the sousd beau was *ot extensive
enough to irradiate the whole plate, the tra*sdueer was
moved about behlad the lead pheet, whlsh was placed elose
to the stareh plats* This gives, the*, essentially a
shadow picture of the sample. Obviously, 1* order to get
the proper exposure time of, Say, two minutes e* a give*
portio* of the plate the total exposure time must be mush
longer, depe*dl*g o* the relative sice of beam a*d sample.
Rather simple experiments Indicate that the acceleration
of the stareh-lodlne reaction, and the mechanics of Image
formation as used here, is a transport phenomenon, the
sound field serving to carry fresh iodine to the plate and
thus maintain the process • For example, a screen of sound
transparent material was placed in front of the plate to
shield it from the unidirectional liquid flow associated
with the sound wave. The action on the starch was much less

%
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21.
marked than without tko gw«e&, and If tho solution were
stirred relatively gently by hand during tho exposure tho
uholo plate darkened amd tho area of ooumd imoidomoo eould
mot ho distinguished* without tho sereem amd 1m a stronger
ooumd field, stirring did mot obliterate tho pattern, hat
tho plato wat darkened amd tho llmoa of tho pattern tomdod
to ho smeared out*
All of tho eVldOnee Imdloatoa that tho technique
described, using ataroh platOa la a weak aolutlom of Iodine,
provides a new, convenient, amd valuable method for tho
atody of ultr&aomlo flold pattormo lm tho laboratory* for
purpoaoa of oomparlaom with othor methods similarly applic­
able, tho phosphor technique amd tho Pohlmam toll wars
Investigated, as deaorlhed below*
THE PHOSPHOR TECHHIQOB
Experimental Arrangement
The prooeduro followed was essentially that deaorlhed
by Rekardt amd Llmdig (6)« Although SOhrolher amd Degner
(SO) exhibited somewhat better pictures, their deaoriptlom
of experimental details is scanty; however, It appears
that tho methods of the two groups were similar* in this
work, the phosphor in the dry form was mined with a suit­
able earrler and laid down on a thin diaphragm to form jgjyg
somosemsitlve element* Duoo sememt thinned proved very

22 9
satisfactory as tke iiwiiv, amd thin phosphor bronze
was ussd as Hit booking* The metal apparently strvid as
well as tits photographic #1In toss* originally used, and
kad the advantage of mot softening under tke action of
the acetone* Tkis phosphorescent sereen formed a boundary
of tko liquid container, or was placed at tko surface of
tko water 1* tko largo tank, so tkat tko pkospkor was
outermost amd tko sound was Imoidomt om tko backing* Tke
pkospkor was Irradiated wltk tko waflltorod light from a
laboratory high pressure mercury ars, allowed to doe ay
for 20-50 seconds* and tko soumd turmed om* Xm a fow
sooomda tko areas of sound imoldomoo wore made apparent
by tko imoroaso la brightness as tko release of tke stored
up energy was aeeeleratod by tke beating offset of tke
sound wawe* If tke sound Is renewed before tke deeay Is
complete, those areas wkiek were bright appear darker tkan
tkalr surroundings slnoe their energy has been depleted*
Si prlmelple the patterns earn be photographed In the usual
way, or somtaet Sprints” ean be nade by applloatlon of a
pleee of out fibs direetly to tke phosphor* tko writer
was unable to obtain photographs with the modified PolaroidbtL
Wd camera used because of the wery low light Intensities*
Ska camera medlfleatlon eonslsted of tke attachment of an

S3.
auxiliary leas for Closer work tkaA allowed for o a tko
*«nera aloxe*
m $ S £ & m 8 £ Bttftftl
Fig. 9 skowo records obtalued by tko eeataet process*
These are similar to tkooo published by lokordt aud Liadig,
no structure being apparent. SCkretber and Pegaer exhibit
results similar but inferior to tkooo of Fig. 6 by tko
•tarOk plato method, bat giro Ao ladleatloa of tko sound
lAtoAoltioo roiialrod.

Eokardt and Lladig roport tko uoo

of 70 vatti Input, which lo a llttlo klgkor tkaA uood kora*
It night bo presumed tkat at ouffloloatly high latoaoltloo
tke ooooadary loboo voald okov op* Tko writer kao aloe
observed at time* a 41growth* of tko pattern, ao might bo
anticipated for & thermal offoot* For fairly high boom
OAorgloo a self«*reversal of the pattora has alao booA
produced.
2t has boom tho writer** experience that tko tine of
trradlatlOA by tko ultraviolet light lo met at all critical,
but that tho louger tho phosphorescence lo allowed to dooay
before applleatlou of tko oouad the bettor lo tko ooatraot.
Several oomerolally available phosphors wore tried, tho
oaly oaeo suitable from tko standpoiAt of doe ay time amd
lAtoAslty of effect belAg the greea and yellow luminescing
oulpkldos of zinc, activated with oopper akd manganese

(a)

*
<b>

(d)

(a)

Phosphor Technique
1073 kc/see.

(a) and (b) are exposures made after the sound field vaa turned
off, and the bean is indicated by the dark areas*

(e) and (d) are

exposures made during sound irradiation, and the bean is indicated
by the light areas* Kastaan Super-Panchro press type B film was
«

placed in immediate contact with the luminescent screen

figure 9

84*
respectively.
Tkis mStked requires tkat tke pkospkoreseeat sereea
^

optically accessible fro* outside tke teak, requires

iaitial excitation of tko pkospkor, aad pkotograpkle task*
alques mist bo used at tko tins of observation for tko
production of a permanent record* Tko metkod kas not boom
skoua to produce results of quality comparable to tkoso
obtained w|tk tko starok plates, aid apparently somewkat
kigker intensities are required for any semblance of a
pattern*
THE POHLklH i t l M

O

m

m

CEK.

sa«.tei§l tm s ts e s tb
48 noted la tko introduction, Poklmaa (28, 27, 28)
kas developed a aotkod for tke Visualisation of aouad
fields consisting essentially of a great many ulauto Rayleigk
disks, so tkat iaeldeat light Is regularly refleeted la
tke areas wkere tke disks are orieated by tke sound beam,
aad diffusely rofleoted la etker areas* Using tkls device
togetker wltk aeoustlo leases, ke kas eoastrueted acoustical
analogues of optical devices, aad la particular kas developed a aotkod for flan deteetloa la solid objects* Wkile
kls doscrlptioa of tke actual sell is sketcky, tke following
laforaatloa Is given* tkla metal foil (tklokaess given as
0*01 am) forms tke back of tke sell, aad glass tke froat) la

@6.
the cell is ft imptftilov of aluminum flakes i* xjrltat, Tke
flakes are described a« tains of about go microns diameter,
and about l.S microns thick* there bains ataut 4 x 106/ m f
Pohlaan shews tkat tka oontraat la greatest fen low aQuad
intensities, and oaXeuXataa tkat tka pattern vislbillty
threskhold corresponds to about 3 x lQ~7»/en$ sound intensity,
thick la ?ery auek lower tkan la required for meat of tke
ether methods*
Several aoXXa answerin^the goneraX deaeriptlon were
built, tke one finally need being IS era* in diameter, about
g ram* thick, with a back of 0*08 ran* pkospkor bronae and
tke front of 1/8* Lucifce* The aluminum flakes used were
tke powder sold commercially for mao in aluminura paint* and
xylene was used for tka suspension* Storeograpkic eleotron
microscope studies indieate tkat tkese flakes range in alee
down from about SO microns, and tkat tkey are tkinnar tkan
tkis* although tkieknees raeasureraents were not feasible*
The writer la indebted to or* H« Beadier for tkese data
from tke eleotron raioroaoope* Tke oell is akewn in fig* 10*
and was supported kerl coatally in tke large tank so tkat
it eould be viewed or photographed frora tke top* Beo&use
tke suspension settles out* tke oell m a t be periodically
agitated to obtain a reasonably uniform suspension* Tke
modified Pelanold-iiand earnera was used to produce tke perm­
anent record*

Fig. 10
POHLMANN

u.

a.

CM.

CELL

■>

setting

1, pictures

taken

immediately

after

sound

turned

on.

Scale

approximately

3/4

2d*
Discussion of Results
•me typo of picture obtained is shown ia Pig* 11,
where it is aoea tkat tke patterns resemble tkose obtained
with tke starch plates* Tkese patterns are abgut two**
thirds actual size. Tke original picture from tke camera
was used to make eoataet prints, aad it is these prlata
wkiek are shown ia Pig# XX, so tkat the black portions
represent the sound beam. Pig* Ilk la of particular interest
in that the cell was deliberately placed off center with
respect to the beam* and structure is apparent which is
more nearly concentric with the cell than with tke sound
beam* This would Haply that tke cell boundaries hare an
influence which would have to be taken into account in
tke interpretation of the pattern* Suck effects are to be
expected since tke suspension Is agitated by the sound
wave, and flow results* It would be expected tkat at very
small intensities this difficulty would be minimised*
Poklmaa kas published no results in the way of near-fteld
patterns, but kas concentrated on geometrical acoustics*
The writer kas been unable to produce pictures of the near*
field using tke pohlmam oell of quality comparable to that
obtained with tke starch plates*
This method again requires optical accessibility,
photographic procedures, and tke cell must be periodically

27*
agitated ia order to maiataia tke koaogeaelty of tko
suspeaslea*
C0HCt?3I0HS
fke use of startk plates ia a dilute solutioa of
iodiao provides a aotkod for tko visuallsatloa aad »eas*
uremeat of ultrasoaie fields which appears to be superior
to exlstlag aetkoda from tke ataadpoiat of quality ©f
record, eaee of obtaiaiag tke record, aad simplicity of
experimeatal arraagemeats* Because of tkeae advaatages Iko
metkod should prove valuable ia tke atody of source patterns,
diffraotioa effects, aad otker iaveatigatioas shore aa
acoustical aaalogue to photography teuld be desirable*

28.
BIBLIOGRAPHY
1.

R. Blr,

2.

G.S. Beaaett,

3.

L. Bergwaiut,

4.

$• ItMllTi

5.

A, Sagnaa and I. Simonot,

••

. .. ... « *

7*

am

] <.

i

Heir. Phya. Acta 9,617

1

J. Aeoust. So®. A®. 23,478

Ultrasoaioa.

(1951)

Joka Wiley sad Bens (Hew
York, 1939)

Aeta Pkysieoekiai. URSS lg,323

......

.

9.

P.J. Ermat,

(1949)

Aauu Pkya. 2,410

3, u w i t . 3oc. Am. 83.80

aad C.W. Hoffmann,

(1948)

PaMa,888,230(1949)

C.R. Faria 288.990

A, Haka*d*'aad 0. Liadig,

(1940)

cat. Faria 887.1834
C.K.

8.

10.

(1936)

(1980)

(1961)

J, Aeouat.Soe. Jan. 84.207 (1958)

11. J. Frenkel, Acta FhyaiaaoklM. UKSS 18,317

(1940)

18, P. Ora&ar and 8, Prvdhemma, C4S. Faria 838.1881 (1948)
13. Virginia Orifflaf, 8. Chaa. ffcya. 18,997

(1960)

14. R. Haul, H.J. Studt and B.B. Ruat, Z. Aagaa. Pfeya. 62.186
t

15. 1. Hledeaaaa and K.H. Boeaek, Z. Pfeys, 104,197
16.
17.

K. Osterkazamal,
and ......
«rR-r^n

(1937)

2, Pkye# 107.273 (1937)

* Proa. lad. Aead. sei, 0.275
(1938J

13. J.Ca Strife***, I,?, Zartmann end C.R. Larkla,
Ja Opt, see. m • £7,832 (1947)
12 w. Keek, G.8. Seller aad a .o . williams Jr,
«T« Acoust. See, A®. 23,168 (1951)
20, A, Kliag sad Hi Kliag, C.K, Paris 223,33

(1946)

29#

81. H. Marinese©, C *R* Paris 808*757 (1956)
« M % * 8el. ©t jBl'^SSS (Hermann #t 01s,
Paris, 1937)

2S* -...
83.

and M, RoggiaJal, <?#£• Paris 200.548 (3-935)

24. K* OstsrliafflBisl, Atatsfc. aielt* j|,73 (1941)
25* H* PinoSr and J* Pouradler, J. Chim. Pfcya. J£,261 (1947)
20. R* PoMlmaa,

3. Pfcys. 107,497 (1937)

27.

8. m » *

28.

...,
... .:nr,.
ta

US.697

(1939)

Angen. Pkys. 1,181 (1948)

29. W. sokssfi, 8« Wtosr»* 105,576 (1937)
30. H* sskrslfesY and w. Degmer, Ann. Pkys. «,275(1950)
31. 7. Timbrell, Hatnrs 167,306 (1951)
32. A* Wslsslsr, «F• Okem, Fkys. 18.1515 (1950)
33.

• fi.w. Cooper and 8. Snyder, J. Am. Ckem. doe.
-----22,1709 (1980)