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Journal of the Acoustical Society of America

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Nov 1988

Volume 84, Issue 5, pp. 1587-1970

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Parametric study of a laser‐generated thermoacoustic signal

Luis J. Gonzalez and Ilene J. Busch‐Vishniac

J. Acoust. Soc. Am. Volume 84, Issue 5, pp. 1587-1597 (1988); (11 pages) | Cited 1 time

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A parametric study of the generation of a sound‐pressure signal generated underwater by a moving thermoacoustic source has been conducted. Numerical results indicate that the source speed and the azimuthal angle between the source initial location and the receiver are the parameters that most affect the pressure signal. Nine signal properties were examined: six time‐dependent properties and three pressure‐dependent properties. Of these, the ratio of the peak to rms pressure is the most sensitive to source variations, and the duration time of the signal is least sensitive.
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43.38.Ar Transducing principles, materials, and structures: general
43.35.Ud Thermoacoustics, high temperature acoustics, photoacoustic effect
43.30.Yj Transducers and transducer arrays for underwater sound; transducer calibration
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Occurrence of transient cavitation in pulsed sawtooth ultrasonic fields

Eveline J. Aymé and Edwin L. Carstensen

J. Acoust. Soc. Am. Volume 84, Issue 5, pp. 1598-1605 (1988); (8 pages)

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Thus far, studies conducted to assess the safety of diagnostic ultrasound have employed sinusoidal sound fields. To evaluate the influence of nonlinearly distorted acoustic fields, this article compares the responses of microbubbles of variable size, exposed to (1) a sinusoidal pulse and (2) a sawtooth pulse. The nonlinear oscillations of a spherical bubble in a viscous compressible liquid stimulated into motion by an ultrasonic pulse are predicted, using a theoretical model for bubble dynamics. The maximum gas pressures inside the bubble when it collapses under the influence of a sinusoid or a sawtooth are deduced. Experimental work on Drosophila larvae exposed to sinusoidal and to sawtooth fields is consistent with the theoretical analysis.
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43.80.Cs Acoustical characteristics of biological media: molecular species, cellular level tissues
43.25.Yw Nonlinear acoustics of bubbly liquids
43.80.Qf Medical diagnosis with acoustics

Alternatives to the impulse response h(t) to describe the acoustical behavior of conical ducts

Joaquim Agulló, Ana Barjau, and Jordi Martínez

J. Acoust. Soc. Am. Volume 84, Issue 5, pp. 1606-1612 (1988); (7 pages) | Cited 6 times

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In unidimensional acoustical systems, the impulse response h(t) at the input section, which describes the pressure evolution originated at this section by the introduction of a flow unit impulse through it, relates pressure p(t) and flow u(t) at the input section by means of the convolution product p=h∗u. If damping and radiation are small, it is interesting to find other functions of faster decay than h(t) in order to improve the convolution convergence. As alternatives to h(t), this article studies the impulse responses h′(t) and h″(t), which correspond to the modified systems that result when coupling the original acoustical system input section to a cylindrical anechoic termination and a conical anechoic termination, respectively. These functions h′(t) and h″(t) are related to the plane‐wave reflection function Rp−(t) and spherical‐wave reflection function Rs−(t), respectively. The comparison of these three impulse responses shows that the use of h′(t) and h″(t), though of faster decay than h(t) in principle, is not always advisable. For conical bores with small truncation, the convolution with h′(t) may lead to numerical instability more easily than that with h(t). On the other hand, the impulse response h″(t) turns out to be divergent for certain geometrical duct configurations, and thus it is useless as a kernel function in a convolution in these cases.
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43.75.Ef Woodwinds
43.20.Mv Waveguides, wave propagation in tubes and ducts

Conical bores. Part I: Reflection functions associated with discontinuities

J. Martínez and J. Agulló

J. Acoust. Soc. Am. Volume 84, Issue 5, pp. 1613-1619 (1988); (7 pages) | Cited 3 times

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Reflection functions associated with discontinuities in conical bores are worked out for the usual cases found in woodwind instruments: taper and diameter discontinuities, open and closed ends, and open and closed holes. Radiation at open ends is considered through the impedance formulation for the open end of a cylindrical tube fitted with an infinite flange. The input impulse response of woodwinds, or related functions such as the plane‐wave or spherical‐wave reflection functions, can be calculated in the time domain by means of these reflection functions through multiple convolutions as shown in the companion article ‘‘Conical bores. Part II: Multiconvolution’’ [Martínez et al., J. Acoust. Soc. Am. 84, 1620–1627 (1988)].
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43.75.Ef Woodwinds
43.20.Mv Waveguides, wave propagation in tubes and ducts

Conical bores. Part II: Multiconvolution

J. Martínez, J. Agulló, and S. Cardona

J. Acoust. Soc. Am. Volume 84, Issue 5, pp. 1620-1627 (1988); (8 pages) | Cited 5 times

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The input impulse response, or related functions such as the plane‐wave or spherical‐wave reflection functions, of a conical bore with discontinuities can be calculated from the reflection functions associated with discontinuities by means of a multiconvolution process. This approach, as alternative to the Fourier transform of the acoustical impedance Z(f), is attractive because of the detailed description it gives of the pressure time evolution inside the bore. However, the calculation may become rather involved if each reflected and transmitted wave is followed individually, and numerical instability may arise whenever the implied reflection functions contain growing exponentials. The first difficulty has been overcome by summing up all outward traveling waves and all inward traveling waves to give a unique outward wave and a unique inward wave. Numerical instability has been avoided by using an iterative convolution algorithm. Internal damping due to viscous and thermal losses has been located at discontinuities and represented by means of damping functions through convolution products. The reflection functions used are presented in the companion article ‘‘Conical bores. Part I: Reflection functions associated with discontinuities’’ [Martínez and Agulló, J. Acoust. Soc. Am. 84, 1613–1619 (1988)].
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43.75.Ef Woodwinds
43.20.Mv Waveguides, wave propagation in tubes and ducts

Analysis of vocal tract parameters in Parkinsonian speech

I. Gath and E. Yair

J. Acoust. Soc. Am. Volume 84, Issue 5, pp. 1628-1634 (1988); (7 pages)

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A method for the analysis of vocal tract parameters is developed, aimed to perform quantitative analysis of rigidity from speech signals of Parkinsonian patients. The cross‐sectional area function of the vocal tract is calculated using pitch synchronous autoregressive moving average (ARMA) analysis. The changes in Parkinsonian subjects of the cross‐sectional area during the utterance of sustained sounds are attributed to both Parkinsonian tremor and rigidity. In order to isolate the effects of the rigidity on the vocal tract from those of the tremor, an adaptive tremor cancellation (ATC) algorithm is developed, based on the correlation of tremor signals extracted from different locations of the speech production system.
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43.72.Ar Speech analysis and analysis techniques; parametric representation of speech
43.70.Dn Disordered speech

Illusory continuity of interrupted speech: Speech rate determines durational limits

James A. Bashford, Jr., Mark D. Meyers, Bradley S. Brubaker, and Richard M. Warren

J. Acoust. Soc. Am. Volume 84, Issue 5, pp. 1635-1638 (1988); (4 pages) | Cited 4 times

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Deleted segments of speech can be restored perceptually if they are replaced by a louder noise. An earlier study of this ‘‘phonemic restoration effect’’ found that, when recorded discourse was interrupted periodically by noise, the durational limit for illusory continuity corresponded to the average word duration. The present study employed a different passage of discourse recorded by a different speaker. Durational limits for apparent continuity of discourse interrupted by noise were measured at the normal (original) playback speed, as well as at rates that were 15% greater and 15% less. At the normal playback rate, once again the limit of continuity approximated the average word duration—but of especial interest was the finding that changes in playback rate produced proportional changes in continuity limits. These results, together with other evidence, suggest that phonemic restorations represent a special linguistic application of a general auditory mechanism (auditory induction) producing appropriate syntheses of obliterated sounds, and that for discourse the limits of illusory continuity correspond to a fixed amount of verbal information, and not a fixed temporal value.
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43.71.Es Vowel and consonant perception; perception of words, sentences, and fluent speech
43.70.Fq Acoustical correlates of phonetic segments and suprasegmental properties: stress, timing, and intonation

The development of skill in producing word‐final English stops: Kinematic parameters

James Emil Flege

J. Acoust. Soc. Am. Volume 84, Issue 5, pp. 1639-1652 (1988); (14 pages)

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It was hypothesized that native English adults would be more skillful in producing word‐final English /p/ and /b/ than native English children who, in turn, would be more skillful in doing so than adult native speakers of a language (Mandarin Chinese) that does not possess word‐final stops. A video tracking system was used to monitor lip and jaw movements. The subjects in all three groups made vowels significantly longer before /b/ than /p/, but the effect seen for the English subjects was three times as large as the Chinese subjects’ effect and depended less on differences in lip closing velocity for /b/ and /p/. The English subjects also showed a difference in duration between /a/ and /i/ that was twice as large as the difference seen for the Chinese subjects. Of the three groups, only the English adults showed significantly greater displacement and peak movement velocity for the final stop consonant of /bap/ than /bab/. This suggested that their central phonetic representations specified a more forceful constriction of the lips for /p/ than /b/. The English adults seemed to compensate more effectively for a bite block in producing the final stops in /bip/ and /bib/. The results obtained for the English children were intermediate to those obtained for the English and Chinese adults, which is consistent with the hypothesized experience‐based differences in level of skill.
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43.70.Aj Anatomy and physiology of the vocal tract, speech aerodynamics, auditory kinetics
43.71.Gv Measures of speech perception (intelligibility and quality)

Patterns of interarticulator phasing and their relation to linguistic structure

Susan Nittrouer, Kevin Munhall, J. A. Scott Kelso, Betty Tuller, and Katherine S. Harris

J. Acoust. Soc. Am. Volume 84, Issue 5, pp. 1653-1661 (1988); (9 pages) | Cited 2 times

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Work by Tuller and Kelso [J. Acoust. Soc. Am. 76, 1030–1036 (1984)] and Kelso et al. [J. Phon. 14, 29–59 (1986)] has demonstrated stable relations between jaw and lip movements in /bV♯CVb/ utterances across rate and stress conditions. Specifically, the onset of lip movement toward the intervocalic consonant was found to be constant with respect to the vowel‐to‐vowel jaw cycle in both time and relative phasing. An attempt was made to replicate and extend this work by investigating interarticulator phase relations for utterances having a broader range of linguistic organization: In addition to rate and stress, syllable structure (open versus closed syllables) and identity of the intervocalic consonant (/p/ vs /m/) were manipulated. Results showed that the upper lip’s lowering onset varied systematically with respect to the jaw vowel cycle as a function of both rate and stress. In addition, syllable structure and consonant identity influenced the relation of lip and jaw gestures. There was a general tendency for any condition that shortened the first vowel to produce earlier onsets of the upper lip relative to the jaw. However, the within‐condition jaw cycle duration variability did not correlate with the within‐condition variability in phase. Thus it seems that stable interarticulator phase relations maintain not only the integrity of phonological structure, as suggested by Kelso et al., but structural integrity at other levels of linguistic organization as well.
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43.70.Bk Models and theories of speech production
43.70.Aj Anatomy and physiology of the vocal tract, speech aerodynamics, auditory kinetics
43.70.Fq Acoustical correlates of phonetic segments and suprasegmental properties: stress, timing, and intonation

Acoustic analysis of compensatory articulation in children

Shari R. Baum and William F. Katz

J. Acoust. Soc. Am. Volume 84, Issue 5, pp. 1662-1668 (1988); (7 pages) | Cited 1 time

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A study was undertaken to explore the effects of fixing the mandible with a bite block on the formant frequencies of the vowels [i a u] produced by two groups of children aged 4 and 5 and 7 and 8 years. Vowels produced in both normal and bite‐block conditions were submitted to LPC analysis with windows placed over the first glottal pulse and at the vowel midpoint. For both groups of children, no differences were found in the frequencies of either the first or second formant between the normal and bite‐block conditions. Results are discussed in relation to theories of the acquisition of speech motor control.
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43.71.Gv Measures of speech perception (intelligibility and quality)
43.70.Aj Anatomy and physiology of the vocal tract, speech aerodynamics, auditory kinetics

Comodulation masking release: Evidence for multiple cues

Joseph W. Hall, III and John H. Grose

J. Acoust. Soc. Am. Volume 84, Issue 5, pp. 1669-1675 (1988); (7 pages) | Cited 14 times

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Signal detection was determined in conditions where the masker was a 10‐Hz‐wide noise band centered on the signal, and in conditions where either a comodulated or noncomodulated noise band (centered at 0.8 times the signal frequency) was also present. Signal frequencies of 500 or 2000 Hz were investigated. In one condition of the first experiment, the signal was exactly the same 10‐Hz‐wide noise band as the masker, added to the masker in phase. This condition was designed to limit the availability of cues based upon dip listening, suppression, beating, or across‐frequency differences in noise envelope correlation, but to afford a cue based upon across‐frequency envelope amplitude difference. The narrow‐band noise signal resulted in approximately the same magnitude of comodulated masking release (CMR) as was found for a pure‐tone signal. This result suggested that one important cue for CMR is an across‐frequency difference in envelope amplitude. Stimulus conditions in the second experiment were intended to disrupt cues of across‐frequency envelope amplitude difference, but to afford cues based upon across‐frequency differences in noise envelope correlation. In this experiment, cues based upon envelope amplitude were impoverished by randomly varying the level of the flanking band from interval to interval, and by adjusting the level in the on‐signal band to be the same in the nonsignal intervals as the level of noise plus signal in the signal interval. Again, substantial CMRs occurred, suggesting that another cue for CMR may be envelope pattern or correlation. The results of these experiments indicated that CMR is probably based upon more than one stimulus variable.
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43.66.Dc Masking
43.66.Mk Temporal and sequential aspects of hearing; auditory grouping in relation to music
43.66.Ba Models and theories of auditory processes

The role of pinna movement for the localization of vertical and horizontal wire obstacles in the greater horseshoe bat, Rhinolopus ferrumequinum

Joachim Mogdans, Joachim Ostwald, and Hans‐Ulrich Schnitzler

J. Acoust. Soc. Am. Volume 84, Issue 5, pp. 1676-1679 (1988); (4 pages) | Cited 5 times

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Six Rhinolophus ferrumequinum were trained to fly through an array of vertical or horizontal wires. Obstacle avoidance performance was measured as the percentage of flights in which the bats did not touch the wires (successful flights). Bats with normal mobile pinnae scored between 70% and 90% successful flights both with vertical and horizontal wires. After surgically immobilizing the pinnae by cutting motor nerves and ear muscles, avoidance performance with vertical wires (horizontal target localization) was unchanged but the percentage of successful flights with horizontal wires (vertical target localization) decreased significantly. This demonstrates the importance of pinna movements for target localization in the vertical plane and supports the hypothesis that scanning movements with pinnae are used by Rhinolophus ferrumequinum for determination of target angle.
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43.66.Gf Detection and discrimination of sound by animals
43.80.Lb Sound reception by animals: anatomy, physiology, auditory capacities, processing

Four channels mediate the mechanical aspects of touch

S. J. Bolanowski, Jr., G. A. Gescheider, R. T. Verrillo, and C. M. Checkosky

J. Acoust. Soc. Am. Volume 84, Issue 5, pp. 1680-1694 (1988); (15 pages) | Cited 16 times

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Although previous physiological and anatomical experiments have identified four afferent fiber types (PC, RA, SA II, and SA I) in glabrous (nonhairy) skin of the human somatosensory periphery, only three have been shown to mediate tactile (mechanoreceptive) sensation. Psychophysical evidence that four channels (P, NP I, NP II, and NP III) do, indeed, participate in the perceptual process is presented. In a series of experiments involving selective masking of the various channels, modification of the skin‐surface temperature, and testing cutaneous sensitivity down to very low‐vibratory frequencies, the fourth psychophysical channel (NP III) is defined. Based on these experiments and previous work from our laboratory, it is concluded that the four channels work in conjunction at threshold to create an operating range for the perception of vibration that extends from at least 0.4 to greater than 500 Hz. Each of the four channels appears to mediate specific portions of the overall threshold‐frequency characteristic. Selection of appropriate neural‐response criteria from previously published physiological data and correlation of their derived frequency characteristics with the four psychophysical channels indicates that each channel has its own physiological substrate: P channel and PC fibers, NP I channel and RA fibers, NP II channel and SA II fibers, and NP III channel and SA I fibers. These channels partially overlap in their absolute sensitivities, making it likely that suprathreshold stimuli may activate two or more of the channels at the same time. Thus the perceptual qualities of touch may be determined by the combined inputs from four channels.
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43.66.Wv Vibration and tactile senses
43.64.Vm Physiology of the somatosensory system

The radiation impedance of the external ear of cat: Measurements and applications

J. J. Rosowski, L. H. Carney, and W. T. Peake

J. Acoust. Soc. Am. Volume 84, Issue 5, pp. 1695-1708 (1988); (14 pages) | Cited 10 times

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The configuration of external ears varies dramatically among mammalian species. In order to relate these structural differences to acoustic performance, it is useful to determine the ‘‘output’’ (radiation) impedance of the external ear. Measurements were made of the radiation impedance ZE of the cat external ear looking out from the location of the tympanic membrane. Freshly excised external ears were coupled to a calibrated sound source at the tympanic ring, and the resulting sound pressure at the source was measured. The ZE calculated from these measurements is masslike at frequencies below 2 kHz and approximately resistive above 4 kHz. The contributions of anatomically distinct sections of the external ear to ZE were assessed by measuring the impedance before and after surgical removal of the pinna flange and of the concha. Mean measurements of the lengths and cross‐sectional areas of components of the external ear are used in a simple model that consists of a uniform tube and an exponential horn; the radiation impedance of the model shows many of the features of the measured ZE’s. Measurements of the input impedance of the middle ear are combined with ZE to infer the diffuse‐field absorption cross section ADF, which is a measure of the ear’s performance as a coupler of acoustic power. It is suggested that ADF is useful for across‐species comparisons of the performance of external and middle ears.
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43.64.Ha Acoustical properties of the outer ear; middle-ear mechanics and reflex
43.64.Tk Physiology of sound generation and detection by animals
43.20.Rz Steady-state radiation from sources, impedance, radiation patterns, boundary element methods
43.80.Lb Sound reception by animals: anatomy, physiology, auditory capacities, processing

Delay‐Doppler resolution performance of large time‐bandwidth‐product linear FM signals in a multipath ocean environment

Jean‐Pierre Hermand and William I. Roderick

J. Acoust. Soc. Am. Volume 84, Issue 5, pp. 1709-1727 (1988); (19 pages) | Cited 4 times

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Active sonar systems that transmit large time‐bandwidth (TW)‐product linear frequency modulated (LFM) waveforms and receive echoes from targets of unknown range and speed can suffer considerable correlation losses that cannot be predicted from conventional (narrow‐band) ambiguity function theory. As is well known, the theory can be modified to include the effects of Doppler distortion on large TW‐product signals by correlating the received signal against a reference that is a time‐compressed version of the transmitted signal. In this article, the effects of multipath (or target highlight structure) and Doppler on the correlation process for rectangular‐weighted large TW‐product LFM waveforms are examined. Gaussian‐weighted waveforms are also considered to examine sidelobe behavior. It is shown that in a multipath environment, the correlator output peak does not generally occur at the correct Doppler reference channel. This is due to the constructive/destructive interference of the summation of complex delay‐Doppler autocorrelation functions associated with each return. A summation technique that identifies the appropriate Doppler reference channel is proposed; this technique allows the target parameters to be estimated if the signal‐to‐noise ratio is sufficiently high.
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43.60.Gk Space-time signal processing, other than matched field processing
43.30.Es Velocity, attenuation, refraction, and diffraction in water, Doppler effect
43.30.Vh Active sonar systems

Effect of transient signal length on cross‐correlation functions in a room

Hirofumi Yanagawa, Yoshio Yamasaki, and Takeshi Itow

J. Acoust. Soc. Am. Volume 84, Issue 5, pp. 1728-1733 (1988); (6 pages)

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An investigation was made of cross‐correlation functions with transient signals between two points, which correspond to both ears of a listener in a room. The interaural cross correlation is closely related to the subjective impressions of sound fields. The study attempted to account in a comprehensive way for the combined effects that initial reflected and reverberation sounds from music or other transient signals have on such impressions. To this end, cross‐correlation functions of the rise and fall of the sound field from transient signals were derived from the impulse responses at two points in the hall. These results were combined with image‐sources distribution patterns derived by the closely located four‐point‐microphone method; then, a comparative explanation was made of the changes with transient time duration of the cross‐correlation functions. Good agreement was found between changes with time in experimentally derived maximal cross‐correlation function values and the changes with time in image‐sources distribution of the sound field.
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43.55.Br Room acoustics: theory and experiment; reverberation, normal modes, diffusion, transient and steady-state response
43.55.Hy Subjective effects in room acoustics, speech in rooms
43.66.Pn Binaural hearing

Superposition of geometries of surface for desired directional reflections in a concert hall

Yoichi Ando and Masaru Sakamoto

J. Acoust. Soc. Am. Volume 84, Issue 5, pp. 1734-1740 (1988); (7 pages)

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In order to obtain desired directional reflections of boundary walls in a concert hall, which may greatly depend upon the frequency range of sound [Y. Ando and Y. Kurihara, J. Acoust. Soc. Am. 80, 833–836 (1986)], a method of superposing geometries of surface is proposed.
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43.55.Fw Auditorium and enclosure design
43.55.Hy Subjective effects in room acoustics, speech in rooms

Effect of traffic noise on the cyclical nature of sleep

G. J. Thiessen

J. Acoust. Soc. Am. Volume 84, Issue 5, pp. 1741-1743 (1988); (3 pages) | Cited 1 time

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Sleep changes from shallow to deep and back again in a cyclical manner with a period of around 90 min. The sleep of 12 subjects, each sleeping for 24 nights, was monitored by EEG. The results indicate that the cyclical nature may be somewhat disturbed by continuous free‐flowing traffic noise, at a level of 60 dB, if, for instance, waking is always considered as the end of one cycle. However, if a cycle is judged from a bird’s‐eye view of the sleep record, then it appears that the average subject persists in his normal cycle and the effect of noise is negligible. But individual differences are great and may even be in opposite directions [G. J. Thiessen and A. C. Lapointe, J. Acoust. Soc. Am. 64, 1078–1080 (1978)], which may result in obscuring real effects when data are averaged over a number of individuals. Defining a ‘‘sleep cycle’’ is of importance in view of reports [M. Herbert and R. T. Wilkinson, Proc. of Congress on Biological Effects on Noise, Dubrovnik, Yugoslavia (1973)] that the disturbance of the sleep rhythm has an effect on performance during the following day.
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43.50.Qp Effects of noise on man and society
43.66.Ed Auditory fatigue, temporary threshold shift
43.66.Mk Temporal and sequential aspects of hearing; auditory grouping in relation to music

Broadband acoustic holography reconstruction from acoustic intensity measurements. I: Principle of the method

Thierry Loyau, Jean‐Claude Pascal, and Paul Gaillard

J. Acoust. Soc. Am. Volume 84, Issue 5, pp. 1744-1750 (1988); (7 pages) | Cited 6 times

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A method, broadband acoustic holography from intensity measurements (BAHIM), is developed for the reconstruction of sources using nearfield acoustic intensity measurement. Nearfield acoustic holography (NAH) is used, but data concerning complex pressure on the hologram are not acquired directly. These data are obtained by processing measurements of active intensity and potential energy density (quadratic pressure). These quadratic values are measured independently at each point on the hologram and therefore do not require a phase reference signal corresponding to the source. This method is thus applicable to sources emitting a broadband spectrum and, more generally, to industrial sources, for which the excitation is not known. The principle of the method is described and the advantages of this type of processing are illustrated by examples.
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43.40.At Experimental and theoretical studies of vibrating systems
43.40.Dx Vibrations of membranes and plates
43.20.Ye Measurement methods and instrumentation
43.40.Yq Instrumentation and techniques for tests and measurement relating to shock and vibration, including vibration pickups, indicators, and generators, mechanical impedance

Elastic constant determination using generation by pulsed lasers

L. F. Bresse, D. A. Hutchins, and K. Lundgren

J. Acoust. Soc. Am. Volume 84, Issue 5, pp. 1751-1757 (1988); (7 pages) | Cited 7 times

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Illumination of a specimen by a pulsed focused laser is known to induce elastic waves, and models are available for both cases of thermoelastic generation and liquid evaporation. In this article, the inverse problem of recovering the elastic constants of a specimen from experimental waveforms recorded on‐ and off‐epicenter is considered. An algorithm, based on nonlinear least‐squares fitting, is presented and has been used on experimental displacement signals recorded on an aluminum plate with a Michelson interferometer. The choice of the receiver position is discussed and experimental results are given.
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43.35.Cg Ultrasonic velocity, dispersion, scattering, diffraction, and attenuation in solids; elastic constants
43.35.Ud Thermoacoustics, high temperature acoustics, photoacoustic effect

A method to account for acoustic microstreaming when predicting bubble growth rates produced by rectified diffusion

Charles C. Church

J. Acoust. Soc. Am. Volume 84, Issue 5, pp. 1758-1764 (1988); (7 pages) | Cited 2 times

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A reinterpretation of existing theory for rectified diffusion, the process by which bubbles in a sound field may grow in radius, is presented in order to quantitate the effect of acoustic microstreaming on bubble growth rates. The 1/t term in the growth rate equation is defined as the ‘‘decay term’’ and t as the ‘‘decay time,’’ the time required for the gas concentration in the liquid contacting the bubble to rise (or fall) from its initial to its final value. In the absence of microstreaming, t is the duration of sonification. In the presence of microstreaming, t may be calculated from the streaming velocity and the bubble radius. A comparison between theory and the experimental results of Eller [A. Eller, J. Acoust. Soc. Am. 46, 1246–1250 (1969)] and of Gould [R. K. Gould, J. Acoust. Soc. Am. 56, 1740–1746 (1974)] shows reasonable agreement in the low kHz range. Theoretical results in the frequency range of 1–10 MHz at 1 and 4 bar are also presented.
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43.35.Bf Ultrasonic velocity, dispersion, scattering, diffraction, and attenuation in liquids, liquid crystals, suspensions, and emulsions
43.25.Nm Acoustic streaming

Sound propagation through random currents using parabolic approximations

R. I. Brent, M. J. Jacobson, and W. L. Siegmann

J. Acoust. Soc. Am. Volume 84, Issue 5, pp. 1765-1776 (1988); (12 pages)

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The influence of random, horizontal, depth‐dependent ocean currents in the parabolic approximation is studied. The current is taken to have a depth‐dependent mean, upon which is superimposed a small fluctuating component. Emphasis is placed on received acoustic intensity. Recently derived parabolic equations including currents are examined using asymptotic and numerical methods. Expressions are derived for the mean and standard deviation of intensity. The fluctuating current component is taken as having an exponential‐cosine autocorrelation function with depth, although other functions could be used. Formulas obtained are sufficiently general to permit many types of depth‐dependent sound speeds and bottom interface models. Current fluctuation effects on intensity moments are illustrated for the specific case of an isospeed channel with a perfectly hard bottom. The acoustic consequences of changes in physical parameters directly related to current fluctuations, such as its standard deviation and correlation length, are discussed. Also exhibited are changes in random current effects on intensity that result from changes in noncurrent related parameters, such as acoustic frequency and channel depth.
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43.30.Bp Normal mode propagation of sound in water
43.30.Ft Volume scattering

Shallow water acoustic studies using an air‐suspended water waveguide model

Jacques R. Chamuel and Gary H. Brooke

J. Acoust. Soc. Am. Volume 84, Issue 5, pp. 1777-1786 (1988); (10 pages)

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A novel experimental technique is introduced that allows multimode interference and coupling due to boundary topography and to the presence of scatterers in shallow water acoustic waveguides to be studied in the absence of radiation and elastic bottom effects. The air‐suspended water waveguide model consists of a water layer bounded above by air and below by a thin rubber membrane supported by pressurized air to counteract the weight of the water. Experimental data on the transmission of transient ultrasonic signals along the ‘‘perfect’’ waveguide are presented and compared with theory. Both experimental and numerical results are used to demonstrate that multiple nondispersed discrete pulses in a waveguide are equivalent to a summation of highly dispersed waveguide modes. Preliminary experimental results are also given demonstrating the propagation of transient acoustic waves in a free‐fluid layer waveguide with sloped or periodic boundaries.
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43.30.Bp Normal mode propagation of sound in water
43.20.Mv Waveguides, wave propagation in tubes and ducts
43.20.Px Transient radiation and scattering

Measurements of upslope wave‐front curvature in a sand‐bottom wedge

H. Hobaek and Evan K. Westwood

J. Acoust. Soc. Am. Volume 84, Issue 5, pp. 1787-1790 (1988); (4 pages) | Cited 2 times

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The results of an experiment designed to measure the curvature of wave fronts traveling upslope in a water wedge having a sand bottom and an air surface are presented. In the experiment, a point source emits a narrow‐band pulse in the deep end of the wedge, and the resulting waveforms are measured on a vertical line in the shallow end of the wedge. Analysis of the recorded waveforms indicates that the wave fronts upslope from the source are curved and that the probable center of the curvature is the apex of the wedge. These results are in agreement with theoretical predictions for a wedge with perfectly reflecting boundaries, where the normal modes are referenced to circular arcs around the apex.
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43.30.Bp Normal mode propagation of sound in water
43.30.Dr Hybrid and asymptotic propagation theories, related experiments
43.20.Mv Waveguides, wave propagation in tubes and ducts

An exact solution to a modified wide‐angle parabolic equation

J. S. Robertson

J. Acoust. Soc. Am. Volume 84, Issue 5, pp. 1791-1793 (1988); (3 pages)

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A modified wide‐angle parabolic equation (MWAPE) [St. Mary et al., J. Comput. Phys. 71, 304–315 (1987)] is studied for a uniform plane‐parallel waveguide with pressure‐release surface and rigid bottom. In this situation, the MWAPE is separable, and the resulting fourth‐order boundary value problem is obtained and solved, which leads to an exact solution of the MWAPE. It is shown that the depth‐dependent eigenfunctions in this instance are identical to those resulting from both the standard parabolic equation and Helmholtz equation in the same channel. Modal wavenumbers for the MWAPE are shown to be equivalent to the first three terms of the Taylor expansion for the Helmholtz wavenumbers, which is one term better than the standard PE wavenumbers. This exact solution can serve as an accuracy benchmark for numerical implementations of the MWAPE.
Show PACS
43.30.Bp Normal mode propagation of sound in water
41.20.Jb Electromagnetic wave propagation; radiowave propagation
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