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Journal of the Acoustical Society of America

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Aug 1984

Volume 76, Issue 2, pp. 345-658

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A more rigorous synthesis of echosonde patterns

S. Adeniyi Adekola

J. Acoust. Soc. Am. Volume 76, Issue 2, pp. 345-368 (1984); (24 pages)

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Presented here is the echosonde (acoustic echosounding) synthesis based on a more rigorous analytical tool than hitherto available. The basic problem addressed in this paper is that of specifying a pattern and solving for the source distribution capable of reproducing the pattern specified. We focus attention on the determination of suitable practical source fields that can provide acceptable pattern approximations to certain prescribed echosonde beams. Numerical and analytical examples discussed, describe patterns synthesizing into physically realizable source fields confined within finite antenna‐aperture regions. Also, other analytical results provided, reveal very clearly that the pattern synthesis problem is not unique. In order to highlight the importance of the present echosonde contribution to the general problem of circular synthesis, we present a brief survey of the synthesis works to date where certain technical problems which still remain unresolved are pointed out. A substantial set of new results for circular echosonde synthesis which has received little attention in the literature, is presented in comprehensive tables for ease of reference. The paper also finally examines an error analysis of certain aspects of the results obtained.
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43.38.Ar Transducing principles, materials, and structures: general
43.20.Rz Steady-state radiation from sources, impedance, radiation patterns, boundary element methods
43.20.Tb Interaction of vibrating structures with surrounding medium
43.30.Vh Active sonar systems

A systems model of the thickness mode piezoelectric transducer

G. Hayward, C. J. MacLeod, and T. S. Durrani

J. Acoust. Soc. Am. Volume 76, Issue 2, pp. 369-382 (1984); (14 pages)

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A new model for piezoelectric ultrasonic transducers is proposed. Using a systems engineering approach, the concept of feedback is used to explain secondary piezoelectric effects and to clearly describe electromechanical interaction. The model is derived from the fundamental piezoelectric equations and it embraces the relevant practical situations where the transducer is subject to arbitrary electrical and mechanical loading. Block diagram representations of the piezoelectric transducer acting as a generator and receiver of ultrasound are developed. The physical significance of each element in the block diagrams are explained to provide a clear and distinct relationship between electrical and mechanical quantities. This permits the factors which control secondary piezoelectric action to be readily defined, along with the importance of this effect on the overall transfer function. It is considered that no other transducer model illustrates these concepts with the same degree of clarity and the technique offers significant advantages over existing transducer analogies. A number of computer simulations and experimental water tank measurements of acoustic wave profiles are presented. Close substantiation of the theoretical analysis is shown.
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43.38.Fx Piezoelectric and ferroelectric transducers
43.38.Ar Transducing principles, materials, and structures: general
43.38.Ew Feedback transducers

Perceptual integration of the murmur and formant transitions for place of articulation in nasal consonants

Kathleen Kurowski and Sheila E. Blumstein

J. Acoust. Soc. Am. Volume 76, Issue 2, pp. 383-390 (1984); (8 pages) | Cited 5 times

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This study reassessed the role of the nasal murmur and formant transitions as perceptual cues for place of articulation in nasal consonants across a number of vowel environments. Five types of computer‐edited stimuli were generated from natural utterances consisting of [m n] followed by [i e a o u]: (1) full murmurs; (2) transitions plus vowel segments; (3) the last six pulses of the murmur; (4) the six pulses starting from the beginning of the formant transitions; and (5) the six pulses surrounding the nasal release (three pulses before and three pulses after). Results showed that the murmur provided as much information for the perception of place of articulation as did the transitions. Moreover, the highest performance scores for place of articulation were obtained in the six‐pulse condition containing both murmur and transition information. The data support the view that it is the combination of nasal murmur plus formant transitions which forms an integrated property for the perception of place of articulation.
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43.70.Fq Acoustical correlates of phonetic segments and suprasegmental properties: stress, timing, and intonation

A reconsideration of acoustic invariance for place of articulation in diffuse stop consonants: Evidence from a cross‐language study

Aditi Lahiri, Letitia Gewirth, and Sheila E. Blumstein

J. Acoust. Soc. Am. Volume 76, Issue 2, pp. 391-404 (1984); (14 pages) | Cited 11 times

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This study explored the claim that invariant acoustic properties corresponding to phonetic features generalize across languages. Experiment I examined whether the same invariant properties can characterize diffuse stop consonants in Malayalam, French, and English. Results showed that, contrary to theoretical predictions, we could not distinguish labials from dentals, nor could we classify dentals and alveolars together in terms of the same invariant properties. We developed an alternative metric based on the change in the distribution of spectral energy from the burst onset to the onset of voicing. This metric classified over 91% of the stops in Malayalam, French, and English. In experiment II, we investigated whether the invariant properties defined by the metric are used by English‐speaking listeners in making phonetic decisions for place of articulation. Prototype CV syllables—[b d] in the context of [i e a o u]—were synthesized. The gross shape of the spectrum was manipulated first at the burst onset, then at the onset of voicing, such that the stimulus configuration had the spectral properties prescribed by our metric for labial and dental consonants, while the formant frequencies and transitions were appropriate to the contrasting place of articulation. Results of identification tests showed that listeners were able to perceive place of articulation as a function of the relative distribution of spectral energy specified by the metric.
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43.71.Hw Cross-language perception of speech
43.72.Ar Speech analysis and analysis techniques; parametric representation of speech
43.70.Fq Acoustical correlates of phonetic segments and suprasegmental properties: stress, timing, and intonation

Perception of temporal differences in speech by ‘‘normal‐hearing’’ adults: Effects of age and intensity

P. J. Price and H. J. Simon

J. Acoust. Soc. Am. Volume 76, Issue 2, pp. 405-410 (1984); (6 pages) | Cited 4 times

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Many older people have greater difficulty processing speech at suprathreshold levels than can be explained by standard audiometric configurations. Some of the difficulty may involve the processing of temporal information. Temporal information can signal linguistic distinctions. The voicing distinction, for example, that separates pairs of words such as ‘‘rapid’’ and ‘‘rabid’’ can be signaled by temporal information: longer first vowel and shorter closure characterize ‘‘rabid’’; shorter vowel and longer closure characterize ‘‘rapid.’’ In this study, naturally produced tokens of ‘‘rabid’’ were low‐pass filtered at 3500 Hz and edited to create vowel and (silent) closure duration continua. Pure‐tone audiograms and speech recognition scores were used to select the ten best‐hearing subjects among 50 volunteers over age 55. Randomizations of the stimuli were presented for labeling at intensity levels of 60 and 80 dB HL to this group and to ten normal‐hearing volunteers under age 25. Results showed highly significant interactions of age with the temporal factors and with intensity: the older subjects required longer silence durations before reporting ‘‘rapid,’’ especially for the shorter vowel durations and for the higher intensity level. These data suggest that age may affect the relative salience of different acoustic cues in speech perception, and that age‐related hearing loss may involve deficits in the processing of temporal information, deficits that are not measured by standard audiometry.
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43.71.Lz Speech perception by the aging
43.66.Sr Deafness, audiometry, aging effects
43.66.Mk Temporal and sequential aspects of hearing; auditory grouping in relation to music

Detection of interaural phase shift between a subaudible and an audible tone

Thomas J. Ayres and T. Dean Clack

J. Acoust. Soc. Am. Volume 76, Issue 2, pp. 411-413 (1984); (3 pages) | Cited 1 time

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Can a shift in interaural phase between a subthreshold signal and an audible contralateral probe tone affect perception of the probe? To obtain an answer, an 800‐Hz tone was presented to both ears. The tone was presented continuously to one ear (−25 to + 10 dB SL) and in a sequence of four bursts per trial to the other ear (+10 dB SL). Interaural phase was reversed for either the second or the fourth burst in a 2 AFC task. Interaural phase‐shift detection threshold (65% correct) varied with the intensity of the continuous signal; across subjects, this threshold varied from −21 to +1 dB SL. When a 300‐or 500‐Hz masking tone was added to the ear with the continuous signal, phase‐shift detection accuracy depended primarily upon the sensation level of the signal rather than its sound pressure level. These findings demonstrate temporal encoding at signal levels well below hearing threshold.
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43.66.Ba Models and theories of auditory processes
43.66.Nm Phase effects
43.66.Pn Binaural hearing

Interaural octave phase‐shift detection and aural harmonic distortion

Thomas J. Ayres and T. Dean Clack

J. Acoust. Soc. Am. Volume 76, Issue 2, pp. 414-418 (1984); (5 pages) | Cited 1 time

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A continuous 400‐Hz tone (60–75 dB SPL) and 250‐msec bursts of an 800‐Hz tone (10 dB SL) were delivered dichotically. Four out of nine listeners were able to detect a 180° interaural phase shift. When a subaudible continuous 800‐Hz tone was added to the ear with the 400‐Hz tone, interaural phase‐shift detection depended on the phase relation of the added tone to the 400‐Hz tone. These results are shown to be consistent with the hypothesis of aural harmonic distortion.
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43.66.Ba Models and theories of auditory processes
43.66.Ki Subjective tones
43.66.Nm Phase effects
43.66.Pn Binaural hearing

Dynamic range and asymmetry of the auditory filter

Brian R. Glasberg, Brian C. J. Moore, Roy D. Patterson, and Ian Nimmo‐Smith

J. Acoust. Soc. Am. Volume 76, Issue 2, pp. 419-427 (1984); (9 pages) | Cited 11 times

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This experiment was designed to measure the shape and asymmetry of the auditory filter over a wider dynamic range than has been measured previously. Thresholds were measured for 2‐kHz sinusoidal signals in the presence of two 800‐Hz‐wide noise bands, one above and one below the signal frequency. The spectrum level of the noise was 45 dB (re: 20 μPa), and the noise bands were placed both symmetrically and asymmetrically about the signal frequency. The deviation of the signal frequency from the nearer edge of each noise band varied from 0 to 0.8 times the signal frequency. Each ear of six subjects was tested, and the subjects’ ages ranged from 22 to 74 years. The auditory filters derived from the data were somewhat asymmetric, with steeper slopes on the high‐frequency side; the degree of asymmetry varied across subjects. The asymmetry could be characterized as a uniform stretching of the (linear) frequency scale on one side of the filter. The dynamic range of the auditory filter exceeded 60 dB in the younger listeners, but the dynamic range and sharpness of the filter tended to decrease with increasing age.
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43.66.Dc Masking
43.66.Ba Models and theories of auditory processes
43.66.Cb Loudness, absolute threshold

Discrimination of fundamental frequency of synthesized vowel sounds in a noise background

Michael T. M. Scheffers

J. Acoust. Soc. Am. Volume 76, Issue 2, pp. 428-434 (1984); (7 pages) | Cited 1 time

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An experiment was carried out, investigating the relationship between the just noticeable difference of fundamental frequency (jndf0) of three stationary synthesized vowel sounds in noise and the signal‐to‐noise ratio. To this end the S/N ratios were measured at which listeners could just discriminate a series of changes in  f0 in the range from 10% to 0.5%. Similar measurements were obtained for pulse trains and for pure tones as a reference for the results. A measure of S/N ratio based on an approximation of the critical bandwidth appeared to provide a fairly good predictor of the masked threshold of each signal, measured in a second experiment. Using this measure, it was found that a given change in the fundamental of a pulse train could be discriminated at a lower S/N ratio than in a pure tone with a frequency equal to that fundamental. The results for the vowel sounds were found to be in between those for a low‐frequency pure tone and those for a pulse train. Owing to the signal‐generation method (viz., changing  f0 by changing the sampling frequency), three cues could in principle be used to discriminate a change in the fundamental of a vowel: A change in the residue pitch, a change in the pitch of a single prominent harmonic, or a change in the spectral envelope of the signal. It can be inferred from the results that the subjects used that particular cue which yielded best performance. Which cue was optimal depended not only on the vowel but also on  f0 and on the presented change in  f0. It seems, however, that the pitch of a single harmonic was the cue most often used. Another interesting result is that changes in  f0 greater than about 5%, could for each signal be discriminated when the signal was just above masked threshold.
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43.66.Fe Discrimination: intensity and frequency
43.66.Hg Pitch
43.66.Dc Masking
43.72.Ne Automatic speech recognition systems
43.71.Bp Perception of voice and talker characteristics

The role of monaural frequency selectivity in binaural analysis

Joseph W. Hall and Mariano A. Fernandes

J. Acoust. Soc. Am. Volume 76, Issue 2, pp. 435-439 (1984); (5 pages) | Cited 1 time

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The relation between the monaural critical band and binaural analysis was examined using an NoSm MLD paradigm, in order to resolve ambiguities about the width of the masking spectrum important for binaural detection. A 500‐Hz pure‐tone signal was presented with a 600‐Hz‐wide band of masking noise to the signal ear. Bands of noise ranging in width from 25 to 600 Hz, or noise notches (imposed on a 600‐Hz‐wide band centered on the signal frequency) ranging in width from 0 to 600 Hz were presented to the nonsignal ear. All noise bands and notches were centered on 500 Hz, the frequency of the signal. The effects of varying bandwidth were radically different from those of varying notchwidth: the MLD changed from zero to approximately 8 dB over a bandwidth range of 400 Hz; for notchwidths, however, the MLD changed 8 dB over a range of only 50 Hz. The results support an interpretation that the fine frequency selectivity of monaural analysis is preserved in peripheral binaural interaction, but that a relatively wide frequency range of critical bands is scanned at a later stage of binaural processing. It was suggested that the wide spectral range of binaural analysis may provide a background against which binaural differences due to the signal are detected.
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43.66.Pn Binaural hearing
43.66.Dc Masking
43.66.Ba Models and theories of auditory processes

The accuracy of hair cell counts in determining distance and position along the organ of Corti

Peter R. Thorne and John B. Gavin

J. Acoust. Soc. Am. Volume 76, Issue 2, pp. 440-442 (1984); (3 pages)

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The relationship between the density of hair cells (cells/mm) and measured distance along the guinea pig organ of Corti was determined using light microscopy and the surface specimen technique. It was demonstrated that the density of inner hair cells (IHC; mean 92.0±2.4) and 1st row of outer hair cells (OHC1; mean 118.7±2.3) did not show significant variation along the organ of Corti except within 0.5–1.0 mm of the apex and base where there was considerable variation between animals in the density of cells. There was a close relationship between the accumulated number of either IHC or OHC1 and distance from the base along the organ of Corti. Distances estimated by hair cell counts were similar to those determined by direct measurement. It is concluded that hair cell counts can be used to reliably estimate distances along the organ of Corti where accurate direct measurement is not possible, such as in scanning electron microscopy.
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43.64.Dw Anatomy of the cochlea and auditory nerve

Aspirin abolishes spontaneous oto‐acoustic emissions

Dennis McFadden and H. S. Plattsmier

J. Acoust. Soc. Am. Volume 76, Issue 2, pp. 443-448 (1984); (6 pages) | Cited 9 times

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Spontaneous oto‐acoustic emissions (OAEs) were measured prior to, during, and following administration of aspirin. The dose schedule was three 325‐mg tablets every 6 h for a total of 16 doses (3.75 days). In every subject studied, all spontaneous OAEs gradually diminished and then disappeared during the drug regimen. Emissions that were initially small disappeared within 14–20 h of beginning the drug regimen (3–4 doses), while initially large emissions took 40–70 h (7–12 doses) to disappear completely. In contrast, the initial size of an emission appeared unrelated to the time required for it to recover to full strength once drug administration ceased. The recovery process was highly idiosyncratic, with the emissions of some subjects returning to full strength within 24 h, while for other subjects, full recovery required several days. In two subjects having multiple emissions in the same ear, the relative sizes of the different emissions often changed greatly during the disappearance and recovery phases. When small frequency shifts appeared for these subjects, they appeared—and were in the same direction—for each of the multiple emissions. In a related experiment, the spontaneous emission was unchanged in one subject who took a drug that inhibits the intracellular entry of calcium ions (verapamil).
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43.64.Kc Cochlear mechanics
43.66.Ba Models and theories of auditory processes

Interaction of cortical evoked potentials to electric and acoustic stimuli

Hugh S. Lusted and F. Blair Simmons

J. Acoust. Soc. Am. Volume 76, Issue 2, pp. 449-455 (1984); (7 pages)

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Evoked potentials to a dichotic stimulus composed of either (1) two binaurally presented tone pips or (2) one tone pip and an electrical pulse to the auditory nerve are recorded from the primary auditory cortex of barbiturate anesthetized cats. The composite stimulus is delivered as a time delayed pair where the interstimulus interval (25 ms) is within the relative refractory period of the evoked potential to either stimulus alone. The amplitude of the cortical potential to the trailing stimulus is compared with its single stimulus amplitude as the frequency of the trailing tone pip is changed from 250 Hz through 40 kHz. There is an optimal frequency range over which the trailing stimulus is suppressed and this range appears directly related to the current of a preceding electrical pulse. The frequency of maximum suppression shifts according to the position of the electrode in the nerve. In some experiments secondary maxima develop, suggesting stimulus current spread from fibers of one cochlear turn into fibers from another turn.
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43.64.Qh Electrophysiology of the auditory central nervous system
43.64.Ri Evoked responses to sounds

On the influence of unequal sub‐array spacing configurations on source localization and the similarity with multipath ranging

J. C. Hassab

J. Acoust. Soc. Am. Volume 76, Issue 2, pp. 456-464 (1984); (9 pages)

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The influence of varied linear array configurations on passive ranging is determined when imperfect measurements of the time delays between the sub‐arrays are available. The exact bias and farfield bias and variance relations on the source range estimates are derived as a function on unequal sub‐array separation. The results are contrasted with those found in the literature on equally separated sub‐arrays to highlight the sensitivity and resulting degradation in performance. It is found, for instance, that the range bias more than doubles when the internal sub‐array is moved from the midpoint to the quarter‐point from either end sub‐arrays and more than quadruples when it is moved from the quarter‐point to the one‐eighth‐point. Since the range variance is related to the true range and to the incurred bias, it degrades much more rapidly. The commonality between array ranging and multipath ranging is also developed for various channels of interests. The optimal placement for the receiving sensor in multipath channels is derived. Though it turns out that the same relations apply to both ranging problems, the existence of a multipath channel will support a longer ranging capability with the baseline now effectively determined by such large parameters as water depth, receiver, and source depths. Such results enable the merger of multisensor data according to their individual merits and the provision for a credence estimate of the source range choice.
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43.60.Gk Space-time signal processing, other than matched field processing
43.30.Wi Passive sonar systems and algorithms, matched field processing in underwater acoustics
43.20.Dk Ray acoustics

Single beam synthesis from thinned arrays

Julius A. Kaiser, Jr.

J. Acoust. Soc. Am. Volume 76, Issue 2, pp. 465-474 (1984); (10 pages)

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A readily steerable, ambiguity‐free beam is formed in real time from a receive aperture containing a sparsely populated array of transducer elements with selected spacings. The system approach utilizes multiple phase‐matched local oscillators in the process of producing at an IF a full set of synthetic spatial frequencies which are similar to the actual spatial frequencies associated with all conventional apertures. A summation of these synthetic spatial frequencies produces the scannable beam with at least as much resolution and freedom from interference as that obtainable from the same size aperture fully filled with closely spaced elements. Beam formation is accomplished either within the system by using a beam forming network or externally by applying the synthesized spatial frequencies to a fully filled transmit array of elements (an autonomous retrodirective system). Experimental measurements at a rf demonstrate that the principles are valid. Superdirectivity, circular arrays (for cylindrical coverage), self‐steering arrays, real‐time holography, passive distance measurement, and frequency/phase modulation recovery from incident carriers are possible extensions of the system approach.
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43.60.Gk Space-time signal processing, other than matched field processing
43.30.Wi Passive sonar systems and algorithms, matched field processing in underwater acoustics
43.28.Tc Sound-in-air measurements, methods and instrumentation for location, navigation, altimetry, and sound ranging

Architectural acoustic measurements using periodic pseudorandom sequences and FFT

W. T. Chu

J. Acoust. Soc. Am. Volume 76, Issue 2, pp. 475-478 (1984); (4 pages)

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The generation and some relevant properties of a class of periodic pseudorandom sequences called the maximum‐length sequence is described briefly. A simple and practical method is proposed to resolve a technical difficulty in using these sequences with FFT processing. The potential advantage of using a maximum‐length sequence as a test signal for architectural acoustic measurements is discussed and illustrated by an example.
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43.55.Br Room acoustics: theory and experiment; reverberation, normal modes, diffusion, transient and steady-state response
43.58.Fm Sound level meters, level recorders, sound pressure, particle velocity, and sound intensity measurements, meters, and controllers

Some gas flow and acoustic pressure measurements inside a concentric‐tube resonator

Joseph W. Sullivan

J. Acoust. Soc. Am. Volume 76, Issue 2, pp. 479-484 (1984); (6 pages) | Cited 1 time

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The one‐dimensional model of the concentric‐tube resonator [J. W. Sullivan and M. J. Crocker, J. Acoust Soc. Am. 64, 207–215 (1978)] assumes that (1) the impedance of the perforation is constant along the length of the flow tube and (2) spatial variations of acoustic pressure in the transverse direction of either tube or cavity are small. Some recent measurements on long resonators have indicated that when mean flow is present, net flow in the cavity, although small relative to that in the tube, affects the impedance in a bidirectional manner resulting in violation of assumption 1. Experiments using microphone probes have demonstrated the validity of assumption 2 provided the tube is perforated axisymmetrically and uniformly. When this is not the case, a circumferential cross mode can be induced which invalidates the one‐dimensional model.
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43.50.Gf Noise control at source: redesign, application of absorptive materials and reactive elements, mufflers, noise silencers, noise barriers, and attenuators, etc.
43.50.Yw Instrumentation and techniques for noise measurement and analysis
47.60.-i Flow phenomena in quasi-one-dimensional systems
43.20.Mv Waveguides, wave propagation in tubes and ducts

An evaluation of the effectiveness of three hearing protection devices at an industrial facility with a TWA of 107 dB

Larry H. Royster, Julia Doswell Royster, and Thomas F. Cecich

J. Acoust. Soc. Am. Volume 76, Issue 2, pp. 485-497 (1984); (13 pages)

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Three hearing protection devices [Siebe Norton Com‐fit earplug, Flents Silenta model 080 earmuff, and E‐A‐R◼ foam earplug] were compared for their effectiveness in preventing both daily temporary threshold shifts (TTS) and threshold variability between sequential annual audiograms for workers in an industrial environment with a TWA of 107 dB. Com‐fit wearers showed significant TTS at 500–4000 Hz from the beginning to the end of the workday. Silenta wearers displayed significant TTS at 500 Hz and nonsignificant improvement at 6000 Hz. E‐A‐R wearers showed significant TTS at 1000–2000 Hz and nonsignificant improvement at 3000–6000 Hz. Statistical analysis indicated that the protection provided by the E‐A‐R plug was significantly better than that of the Com‐fit plug at 500–4000 Hz, and significantly better than the protection of the Silenta muff at 500, 3000, and 4000 Hz. Employees’ last four annual audiograms prior to the start of the TTS study were evaluated to compare the wearer groups’ mean values of the %BWs statistic (sequential percent better or worse). Previous research indicates that the %BWs statistic for a properly protected population with past audiometric test experience will be less than 30%. The E‐A‐R group showed an acceptable %BWs value (26%), but the Silenta wearers (45%) and Com‐fit wearers (53%) showed excess threshold variability in threshold measurements from year to year.
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43.50.Qp Effects of noise on man and society
43.66.Ed Auditory fatigue, temporary threshold shift
43.50.Jh Noise in buildings and general machinery noise
43.66.Ts Auditory prostheses, hearing aids

Measurement of attenuation and dispersion using an ultrasonic spectroscopy technique

Ronald A. Kline

J. Acoust. Soc. Am. Volume 76, Issue 2, pp. 498-504 (1984); (7 pages) | Cited 5 times

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An ultrasonic spectroscopy technique for the simultaneous, wideband measurement of attenuation and dispersion in solids is described. The technique is based on Fourier analysis of digitized ultrasonic waveforms. Results are compared with discrete frequency measurements of these properties with good agreement observed.
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43.35.Cg Ultrasonic velocity, dispersion, scattering, diffraction, and attenuation in solids; elastic constants
43.35.Yb Ultrasonic instrumentation and measurement techniques
43.58.Kr Spectrum and frequency analyzers and filters; acoustical and electrical oscillographs; photoacoustic spectrometers; acoustical delay lines and resonators

A mechanism for the generation of cavitation maxima by pulsed ultrasound

H. G. Flynn and Charles C. Church

J. Acoust. Soc. Am. Volume 76, Issue 2, pp. 505-512 (1984); (8 pages) | Cited 4 times

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A train of 1‐MHz pulses can generate maxima of cavitation activity [V. Ciaravino, H. G. Flynn, and M. W. Miller, Ultrasound Med. Biol. 7, 159–166 (1981)] at pulse lengths of 6 and 60 ms and at pressure amplitudes, PA, between 5.4 and 9.4 bars (or intensities between 10 and 30 W/cm2). Generation of maxima at PA between these limits on pressure amplitude implies that the increase in cavitation activity originates from gas nuclei with radii lying in a critical size range centered at about 0.08 μm. The mechanism proposed for this phenomenon suggests that nuclei in this critical range are unstabilized nuclei generated in one pulse and surviving to the next with an appreciable fraction of the survivors lying in the critical range. Transient cavities that grow from such small nuclei are shown to behave as isolated mechanical systems that on reaching maximum size collapse as imploding spheres. The maximum pressures reached in such imploding cavities would then approximate those calculated for the spherical collapse of cavities. The occurrence of the observed maxima is ascribed to the spherical collapse of transient cavities.
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43.35.Ei Acoustic cavitation in liquids

Imaging in a scanning photoacoustic microscope

I. J. Cox and C. J. R. Sheppard

J. Acoust. Soc. Am. Volume 76, Issue 2, pp. 513-515 (1984); (3 pages)

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Imaging in a scanning photoacoustic microscope (SPAM) is analyzed using Fourier imaging concepts. In particular, the spatial frequency response and the resolution of the instrument are examined. It is shown that in the general case, the imaging is object dependent. However, for the special cases of negligible thermal diffusion or where the specimen is either optically uniform or acoustically and thermally uniform, explicit expressions for the spatial frequency response are derived. It is shown that a SPAM may exhibit superresolution provided an acoustic lens is used rather than a large area detector.
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43.35.Sx Acoustooptical effects, optoacoustics, acoustical visualization, acoustical microscopy, and acoustical holography
43.60.Qv Signal processing instrumentation, integrated systems, smart transducers, devices and architectures, displays and interfaces for acoustic systems

Measurement of normal surface displacements for the characterization of rectangular acoustic array elements

R. L. Jungerman, P. Bennett, A. R. Selfridge, B. T. Khuri‐Yakub, and G. S. Kino

J. Acoust. Soc. Am. Volume 76, Issue 2, pp. 516-524 (1984); (9 pages) | Cited 2 times

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The performance of elements in transducer arrays is evaluated, at various stages of construction, using an interferometric optical probe that is capable of measuring acoustic displacements of the order of 3 × 10−4 Å. The vertical displacement is first measured on a single piezoelectric strip without matching layers or backing, and is compared with variational calculations of the surface displacement for both the open‐ and short‐circuit modes. Good agreement is obtained between experiment and theory. The measurement is repeated after a matching layer is added, then after a backing is added, and finally with the array water loaded after final completion. Our experimental results are in excellent agreement with theory, where theoretical predictions are available. Laser probe measurements are used to evaluate the cross‐coupling between array elements and predict the farfield illumination pattern of the array elements.
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43.35.Yb Ultrasonic instrumentation and measurement techniques
43.38.Ar Transducing principles, materials, and structures: general

Using ultrasonic SH waves to estimate the quality of adhesive bonds: A preliminary study

Ching H. Yew

J. Acoust. Soc. Am. Volume 76, Issue 2, pp. 525-531 (1984); (7 pages) | Cited 1 time

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A preliminary study using horizontal shear waves (SH waves) in a bonded plate to estimate the bonding strength of adhesive is presented in this paper. The essence of the method is based on the observation that the characteristics of SH waves in a bonded plate are dependent upon the bonding stiffness of the adhesive; thus, an estimation of the adhering strength can be made by observing the behavior change of these wave motions. An adhesive can, in general, by modeled as a viscoelastic material. The mechanical properties determined by subjecting the material to a pure shear deformation are therefore the most pertinent properties that characterize the cohesive strength of the adhesive. An SH wave produces a pure shear deformation in the adhesive layer in a direct manner. In this study, a long aluminum strip is bonded to the surface of a large aluminum block. An SH wave is imparted to one end of the strip. The shear wave motions in the strip are periodically monitored at sequential times as the adhesive cures. The results indicate that (1) there are two measurable modes of SH waves in the strip during the early stage of adhesive curing and (2) the amplitude of the second mode SH wave decreases as the adhesive cures, finally disappearing after the adhesive curing process is completed. This study has successfully shown that the bonding stiffness of adhesives can be estimated by observing the amplitude change of the second mode SH‐wave motions in the adhered plate.
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43.35.Zc Use of ultrasonics in nondestructive testing, industrial processes, and industrial products
43.35.Yb Ultrasonic instrumentation and measurement techniques
43.20.Bi Mathematical theory of wave propagation

The synoptic sound‐speed field of a warm‐core Gulf Stream ring

James J. Bisagni and Peter Cornillon

J. Acoust. Soc. Am. Volume 76, Issue 2, pp. 532-539 (1984); (8 pages)

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A synoptic expendable bathythermograph survey of the warm‐core Gulf Stream ring 81‐D, conducted in September 1981 when the ring was located 550 km south of Halifax, Nova Scotia, provided the basis for a detailed study of the ring’s sound‐speed field. Salinities used for computing sound speed were derived from nonsynoptic conductivity–temperature–depth data collected during the survey. Analysis of the sound‐speed field, using vertical and horizontal sections and satellite imagery, revealed the ring’s typical high sound‐speed core, but also showed increased horizontal and vertical gradients along the ring’s western margin as compared to its eastern side. This asymmetry appears to be related to a surface streamer of warm, higher sound‐speed Gulf Stream water overlying colder, lower sound‐speed slope water, resulting in a subsurface sound duct centered 100 m below the surface along the ring’s western margin. The subsurface duct and increased vertical gradient resulted in 30–50 dB greater loss at depths of 100 and 200 m in the ring’s eastern margin as compared to its western side and center. Strong ray channeling and refraction of a 2000‐Hz source at a depth of 100 m was also noted. Based on these observations and predictions, warm‐core rings may possess regions of increased acoustic range dependence due to the interactions of waters along their margins.
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43.30.Es Velocity, attenuation, refraction, and diffraction in water, Doppler effect
92.10.Vz Underwater sound

Three models of global ocean noise

Roger Dashen and Walter Munk

J. Acoust. Soc. Am. Volume 76, Issue 2, pp. 540-554 (1984); (15 pages) | Cited 5 times

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The vertical directionality of ambient low‐frequency (shipping) noise at midlatitudes has been measured by Wales and Diachok [S. C. Wales and O. I. Diachok, J. Acoust. Soc. Am. 70, 577–582 (1981)] in the Atlantic and by Williams and Fisher (R. B. Williams, personal communication. The measurements were taken in October 1979) in the Pacific. At the sound axis the angular distribution in intensity is flat from 0° (horizontal) up to the inclination of the surface‐limited rays. The intensity falls off sharply for steeper rays (which are associated with lossy bottom reflections). This observed flat angular distribution is in contrast with the bimodal distribution (peaked near the inclinations of surface‐limited rays and zero for flat rays) which is expected from surface sources in a range‐independent environment. A flat angular distribution is equivalent to an equal partition of energy among modes; once such equipartition is attained, the distribution remains unaltered with propagation (or scattering) in a lossless channel. The simplest model consists of surface sources generating rays of steep axial inclination, which are then scattered into flat rays by internal waves throughout the ocean volume. The model fails because of the weakness of the scatterers, requiring 104 km for equipartition. There are two regions for the noise energy to couple directly into flat (near‐axial) rays: (i) at high latitudes where the rising sound axis intersects the surface, and (ii) at the continental slope where the sound axis intersects the rising bottom. The second model consists of sources in the high latitude duct (where the sound axis is essentially at the surface), with energy broadly partitioned among modes from the very start (dipole sources in a linear sound speed gradient give precisely equipartition). Subsequently, the energy is ducted downward along the axis into midlatitudes, preserving equipartition. This model fails because of the low density of shipping at high latitudes. In the third model, the steeply descending rays from coastal shipping are bounced into flat near‐axial rays over the continental slope, as proposed by Wales and Diachok. Although there is some mystery as to how this will lead to the observed high degree of mode equipartition, we conclude (reluctantly) that reflections at the continental slope are probably the dominant mechanism for getting energy into the flat rays.
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43.30.Nb Noise in water; generation mechanisms and characteristics of the field
43.30.Bp Normal mode propagation of sound in water
92.10.Vz Underwater sound
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