bluuebunny/crossref_metadata_2025 huggingface dataset:
Theoretical basis of a method for measuring the complex sound speed of fluids at low frequencies by using an actively terminated acoustic waveguide
Authors: Rudgers Anthony J.
Published: October 2005

In principle, a standing-wave pressure node can be established at (almost) any cross section in an actively terminated fluid-filled acoustic waveguide of fixed length at any frequency, even if the waveguide length is less than one-half the wavelength of the sound in the waveguide. By varying, at fixed frequency, the excitation of one of the transducers terminating the waveguide, this standing-wave node can be acoustically displaced in the waveguide by a known distance. This standing-wave-node displacement is the basis for a method by which one can, in principle, measure the sound speed and absorption coefficient of the fluid filling the waveguide. The equations for determining a value for the complex sound speed of the fluid (from which phase-speed and absorption-coefficient values can be obtained) are given for two different hypothetical implementations of the method. One implementation requires an array of three equispaced pressure sensors to be placed in the waveguide, and the other requires that an array of four such sensors be used. Only the analytic basis of the method is described; no experimental results are reported. The method is proposed as a possible means by which acoustic interferometric techniques can be extended to measure the properties of liquids and gases at frequencies lower than those that can be accommodated with present measurement devices.
Application of a piezoelectric flexural vibrator to a car horn
Authors: Kudo Michio , Fukami Tatuo , Hayashibe Rinpei
Published: October 2005

A piezoelectric ceramic horn for automobiles has been successfully fabricated using a unimorph type of flexural composite vibrator. Insertion of an appropriate metal disk between the ceramic and the diaphragm has made it possible to generate a sound-pressure level greater than 110 dB. Electrically driving the horn transmitter with an amplitude modulated signal has significantly improved the tone quality.
Comment on ‘‘Air absorption of motor vehicle noise’’ [J. Acoust. Soc. Am. 8
, 561–568 (1986)]
Authors: Verhas Hugo P.
Published: October 2005

It is found that Makarewicz’ article ‘‘Air absorption of motor vehicle noise’’ [J. Acoust. Soc. Am. 80, 561–568 (1986)] is confusing: Quantities like reception time t, emission time t′, observed frequency f ′, and emitted frequency f are not well defined and have various meanings; for instance, t and t′ in Fig. 1, respectively Fig. 1(a). Revised equations are presented. The revision reveals that the computations in Makarewicz’ article produce overestimated results and it is found that the content of the article is misleading. Corrections to these computations are presented.
Temporal integration in normal hearing, cochlear impairment, and impairment simulated by masking
Authors: Florentine Mary , Fastl Hugo , Buus So/ren
Published: October 2005

To assess temporal integration in normal hearing, cochlear impairment, and impairment simulated by masking, absolute thresholds for tones were measured as a function of duration. Durations ranged from 500 ms down to 15 ms at 0.25 kHz, 8 ms at 1 kHz, and 2 ms at 4 and 14 kHz. An adaptive 2I, 2AFC procedure with feedback was used. On each trial, two 500-ms observation intervals, marked by lights, were presented with an interstimulus interval of 250 ms. The monaural signal was presented in the temporal center of one observation interval. The results for five normal and six impaired listeners show: (1) normal listeners’ thresholds decrease by about 8 to 10 dB per decade of duration, as expected; (2) listeners with cochlear impairments generally show less temporal integration than normal listeners; and (3) listeners with impairments simulated using masking noise generally show the same amount of temporal integration as normal listeners tested in the quiet. The difference between real and simulated impairments indicates that the reduced temporal integration observed in impaired listeners probably is not due to splatter of energy to frequency regions where thresholds are low, but reflects reduced temporal integration per se.
Rate coding model for discrimination of simple tones in the presence of noise
Authors: Erell Adoram
Published: October 2005

The predictions of a rate coding model for frequency and amplitude jnd’s in the presence of noise are presented for a 1-kHz, 100-ms tone. The model for the neural response incorporates physiological data on dynamic range distribution and rate suppression. A central processor is assumed to estimate the tone frequency, or amplitude, from the tone-evoked rate increment profile. This central processor acts like an ideal detector with respect to the neural noise. The effects of the neural noise as well as the signal variability on the discrimination performance level are evaluated, and the signal variability is found to be significant. The combined effect of threshold distribution, rate suppression, and signal variability make the jnd’s practically invariant with noise level, in accordance with published psychophysical data. The values of the frequency jnd at high signal-to-noise ratio, however, are borderline in their consistency with the data. A more obvious discrepancy exists between the model and the psychophysical data regarding the ratio of frequency to amplitude Weber fractions, which can be resolved only by modifying the model auditory filters to be five times sharper than those measured in cats.
The development of a discrete transform for the Wigner distribution and ambiguity function
Authors: Poletti Mark A.
Published: October 2005

A theoretical basis for the development of the discrete Wigner distribution and ambiguity function is presented that is based on the temporal and spectral properties of the two-dimensional Wigner kernel function. This two-dimensional description is helpful in visualizing the various functions and shows that the increase in the number of points required to compute the discrete Wigner distribution is a natural consequence of the definition of the kernel, and that it does not contradict the Nyquist sampling theorem. A generalized set of pseudofunctions is introduced that involves applying a two-dimensional weighting function to the Wigner kernel or its two-dimensional Fourier transform, resulting in a Wigner distribution that is weighted or smoothed in time or frequency. Two forms of the Wigner distribution are derived. The first is a pure Wigner distribution without any windowing of the kernel that may be computed over the entire data set. The second involves the general set of pseudo-Wigner distribution that may be calculated over a subset of the data set. The discrete Wigner distribution of the analytic signal is also developed, and it is shown that the number of points may be reduced by a factor of 2, in the same way that the number of points required to represent the discrete analytic signal may be reduced. The discrete ambiguity function is developed along with the discrete Wigner distribution and it is shown that the four two-dimensional functions are interrelated by discrete one- and two-dimensional Fourier transforms.
Mechanical displacement induced in a piezoelectric structure: Experimental measurement by laser interferometry and simulation by a finite element method
Authors: Gindre Marcel , Urbach Wladimir , Coursant Roger H. , Fink Mathias
Published: October 2005

From the knowledge of piezoelectric material tensorial components one can, by the finite element method, calculate the electrical impedance versus frequency and simulate the mechanical deformation of piezoelectric bars. Here, the simulation results obtained with lead zirconate-titanate and lead titanate ceramics are reported. In order to check the validity of the simulation, interferometric measurements of the mechanical deformation amplitude were performed. It is shown that these measurements are able to reveal the inhomogeneity of the materials under study and that a small error in the tensorial parameter absolute values leads to an inconsistent picture of simulated mechanical deformation.
The relation between loudness and intensity difference limens for tones in quiet and noise backgrounds
Authors: Rankovic Christine M. , Viemeister Neal F. , Fantini Deborah A. , Cheesman Margaret F. , Uchiyama Craig L.
Published: October 2005

Recent studies of the relation between loudness and intensity difference limens (DLs) suggest that if, two tones of the same frequency are equally loud, they will have equal relative DLs [R. S. Schlauch and C. C. Wier, J. Speech Hear. Res. 30, 13–20 (1987); J. J. Zwislocki and H. N. Jordan, J. Acoust. Soc. Am. 79, 772–780 (1986)]. To test this hypothesis, loudness matches and intensity DLs for a 1000-Hz pure tone in quiet and in a 40-dB SPL spectrum level broadband noise were obtained for four subjects with normal hearing. The DLs were obtained in both gated- and continuous-pedestal conditions. Contrary to previous reports, equally loud tones do not yield equal relative DLs at several midintensities in the gated condition and at many intensities in the continuous condition. While the equal-loudness, equal-relative-DL hypothesis is not supported by the data, the relation between loudness and intensity discrimination appears to be well described by a model reported by Houtsma et al. [J. Acoust. Soc. Am. 68, 807–813 (1980)].
Detection, loudness, and discrimination of five-component tonal complexes differing in crest factor
Authors: Preece John P. , Wilson Richard H.
Published: October 2005

The detection, loudness, and discrimination performances of subjects with normal hearing were assessed using 3 five-component tonal complexes (1020–1100 Hz) with crest factors of 1.8, 2.6, and 3.2. The 3 five-component tonal complexes were: (1) equally detectable in broadband noise when presented at equal rms amplitude; (2) perceived as equally loud when presented at essentially equal rms amplitude; and (3) discriminable from one another when presented at equal loudness. The present data indicate that listeners can make discriminations on the basis of amplitude variations.
Shear wave logging in semi-infinite saturated porous formations
Authors: Schmitt D. P. , Zhu Y. , Cheng C. H.
Published: October 2005

Recent theoretical and experimental studies have demonstrated the interest of using nonaxisymmetric sources, such as dipole and quadrupole, to record shear wave events in any kind of formation (fast or slow). Nonaxisymmetric sources excite surface waves whose Airy phase is predominant in the records at intermediate frequencies (≂3 to 6 kHz). They are referred to as the flexural and screw modes, respectively, for the dipole and the quadrupole sources. Their dispersion and attenuation are studied in a fluid-filled borehole embedded in a homogeneous saturated porous formation. The two-phase medium is modeled using Biot’s theory modified in accordance with the homogenization theory. Calculation of synthetic full waveform logs is also performed using the discrete wavenumber method. Whatever the formation, the most reliable information that can be extracted from low-frequency parts of the wavetrains is the formation shear wave velocity and attenuation. It is of great interest in the inversion of Stoneley wave velocity and attenuation for the evaluation of in situ permeability. In the presence of fast formations, the attenuation of the Airy phase of both the flexural and screw modes is sensitive to the in situ permeability. The same conclusion holds for the slow formations only when they are saturated by a fluid of low viscosity and high compressibility.
Burying straw men in imaginary graves: A reply to Kewley-Port, Watson, and Foyle (1988)
Authors: Pastore Richard E.
Published: October 2005

Kewley-Port, Watson, and Foyle [J. Acoust. Soc. Am. 83, 1133–1145 (1988)] describe a study that uses several different procedures to measure thresholds for stimuli whose components differ in temporal onset. Unfortunately, misunderstandings and misconceptions (shared with other recent publications) resulted in conclusions that are both unnecessary and unwarranted. The Kewley-Port et al. article is discussed in terms of often replicated published findings on temporal order thresholds, and current misconceptions of perceptual concepts and models.
Some remarks on Pastore (1988)
Authors: Watson Charles S. , Kewley-Port Diane
Published: October 2005

Pastore [J. Acoust. Soc. Am. 84, XXX–XXX (1988)] has written a lengthy response to Kewley-Port, Watson, and Foyle [J. Acoust. Soc. Am. 83, 1133–1145 (1988)]. In this reply to Pastore’s letter, several of his arguments are addressed, and new data are reported which support the conclusion of the original article. That conclusion is, basically, that the temporal acuity of the auditory system does not appear to be the origin of categorical perception of speech or nonspeech sounds differing in temporal onsets.
Influence of ground reflection on measurements involving bands of noise
Authors: Bass Henry E. , Raspet Richard , Noble John
Published: October 2005

It has been shown [L. C. Sutherland and H. E. Bass, J. Acoust. Soc. Am. 66, 885–894 (1979)] that frequency-dependent atmospheric absorption can lead to a propagation loss for a band of noise that is much different from that for a pure tone at band center. In the presence of a ground surface, interference can also cause the sound amplitude to vary rapidly with frequency. When this occurs, the level measured for a pure tone can differ dramatically from that measured for a band of noise. Accurate treatment of this difference requires integration over the bandpass of the fractional octave band filter used in the measurement. Example calculations have been performed for a typical filter. These examples form a basis for general guidelines to be used when comparing theory to measurements.
Biot theory and stress–strain equations in porous sound-absorbing materials
Authors: Depollier Claude , Allard Jean F. , Lauriks Walter
Published: October 2005

The Biot model has been used extensively for the last 30 years. The equations of continuity of the models traditionally used to predict the acoustical properties of sound-absorbing materials are compared here to simplified expressions obtained from the Biot model. From this comparison, it is possible to point out inconsistencies in traditional models.
Diffuse field response, receiver impedance, and the acoustical reciprocity principle
Authors: Shaw E. A. G.
Published: October 2005

When an acoustical receiver of uncertain directivity, such as the external ear, is immersed in a diffuse sound field, there is a unique relationship between the response at the receiver diaphragm, the acoustic impedance of the diaphragm, and the impedance presented to the diaphragm by the receiver body and sound field. An explicit analysis based on the reciprocity principle shows that this relationship has broad validity subject to the inclusion of a radiation efficiency factor to allow for losses within the receiver itself. The overall performance of the receiver as a diffuse-field sound collector can be expressed in terms of an equivalent sound absorbing sphere the cross-sectional area of which cannot exceed λ2/4π.
Speech masking. II: Simultaneous masking thresholds under ‘‘naturalistic’’ listening conditions
Authors: Spiegel Murray
Published: October 2005

This article investigates the role of listening conditions in determining thresholds for probe tones masked by natural speech. These thresholds are of interest because they are a sensitive probe of the activity profile, or spectrum, of sounds such as speech in the auditory system. Most human performance tests are carried out under highly artificial listening conditions, which may not reflect how people listen to speech in common listening environments. In this study, reference conditions (similar to minimal uncertainty listening conditions used in many performance tests) were compared to a ‘‘naturalistic’’ listening condition and to another, intermediate, condition. In the naturalistic listening condition, listeners did not know the frequency or the position of probe tones; additionally, they were required to attend to the semantic content of sentences. In the reference condition, listeners knew the frequency and position of probe tones masked by single syllables. Average thresholds were elevated by 4 dB in the naturalistic listening condition with respect to the reference condition, and thresholds tended to be elevated more for higher-frequency probe tones. The results provide previously unknown information about the resolution of speech sounds in the auditory system during speech comprehension.
Broadband repetition pitch: Spectral dominance or pitch averaging?
Authors: Warren Richard M. , Bashford James A.
Published: October 2005

Repetition pitch (RP) produced by mixing noise with its restatement was studied under a variety of delays and filtering conditions. Both normal or cophasic mixtures (RP+) and polarity inverted or antiphasic mixtures (RP−) were used. In keeping with earlier reports, RP+ having a delay of t seconds produced a pitch of 1/t Hz for all spectral regions examined. Broadband RP− diverged from 1/t Hz in keeping with the literature, but the pitches heard under novel filtering conditions indicated that (contrary to some current theories) RP− is a weighted average of the different pitches contributed by different spectral regions. Polarity inversion of an echo introduces additional frequency-dependent delays, and it is suggested that the corresponding RP− at local regions of the basilar membrane reflects a temporal domain analysis based on the sum of these two types of delays.
Masking patterns in the bullfrog (R
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Authors: Freedman Edward G. , Ferragamo Michael , Simmons Andrea Megela
Published: October 2005

Responses of individual eighth-nerve fibers in the bullfrog (Rana catesbeiana) were measured to tone bursts at best frequency against a background of continuous, broadband masking noise. These data were used to calculate critical masking ratios to describe the fibers’ responses to tones embedded in noise. In the frequency response range of the amphibian papilla (100–1000 Hz), critical ratios increase with tone frequency. Critical ratios of basilar papilla fibers (1000–2000 Hz) are generally higher than those of amphibian papilla fibers. Critical ratios are also significantly related to fiber threshold such that fibers with high thresholds, regardless of their best frequencies, have higher critical ratios and are thus less selective to signals embedded in noise. Critical ratios based on neural responses show a somewhat different frequency-dependent trend than do critical ratios based on psychophysical data presented previously for this species [A. M. Simmons, J. Acoust. Soc. Am. 83, 1087–1092 (1988a)]. In addition, these neural critical ratios do not appear to be level independent, as are psychophysical critical ratios. The data suggest that frequency selectivity of hearing in the bullfrog as measured behaviorally is probably not mediated solely by spectral filtering in the auditory periphery.
Synchrony-dependent autocorrelation in eighth-nerve-fiber response to rippled noise
Authors: ten Kate Jaap H. , van Bekkum Marc F.
Published: October 2005

Autocorrelograms and interval and delay histograms of the eighth-nerve-fiber response in cats to cosine noise were recorded. A good detectability level for the delay oscillations in the autocorrelograms was always found, when the fiber had a high value of the synchronization index at characteristic frequency (CF). In order to study their relationship, autocorrelograms for cosine noise stimulation were computed by the substitution of synchronization indices in the Poisson distribution formulas for higher-order intervals. The approach was made possible through a further exploration of Johnson’s synchronization theory [D. H. Johnson, ‘‘The response of single auditory-nerve fibers in the cat to single tones: synchrony and average discharge rate,’’ Ph. D. thesis, MIT, Cambridge, MA (1974)]. It was shown that computed autocorrelograms somewhat resembled experimental ones. The differences between them concerned the envelopes of the ‘‘onset’’ and ‘‘delay’’ oscillations, viz., in their constrictions and amplitudes. These constrictions were shown to be significant only in recordings at delays ≥4/CF, corresponding to the dominant region for human repetition pitch.
Formulation for quantitative performance evaluation of holographic imaging
Authors: Lee Hua
Published: October 2005

In this article, an alternative approach is proposed to quantitatively evaluate image quality of holographic reconstructions. Instead of the conventional approach outlined by the Rayleigh resolution criterion, this approach describes the image quality in terms of the certainty of the estimation of the source distribution. Given the classical imaging parameters, this formulation gives results in exact agreement with the Rayleigh criterion. In addition, this formulation can be extended to quantitatively evaluate the degradation factors such as aperture offset, wave field sampling, quantization error, noise level, and phase-only data acquisition that are not considered in the formulation of Rayleigh resolution criterion. This approach can be also used for quantitative performance evaluation of enhancement algorithms for comparison purposes.
The time-domain solution of the wide-angle parabolic equation including the effects of sediment dispersion
Authors: Collins Michael D.
Published: October 2005

The wide-angle time-domain parabolic equation (TDPE), which is the inverse Fourier transform of the wide-angle parabolic equation (PE), is derived. A numerical solution for the model is described and a benchmark calculation is presented. The narrow-angle TDPE is also considered and its error is analyzed and compared with the error of the narrow-angle PE. The TDPE is compared with the progressive wave equation, which is shown to be restricted to narrow-angle propagation for practical purposes. In the sediment, attenuation is assumed to depend linearly on frequency and the corresponding causal dispersion law is assumed. The model is used to show that the effect of sediment dispersion on pulse propagation in the ocean can be significant.
Signal attenuation due to cavity leakage
Authors: Sherman Max H. , Modera Mark P.
Published: October 2005

The propagation of sound waves in fluids requires information about three properties of the system: capacitance (compressibility), resistance (friction), and inductance (inertia). Acoustical design techniques to date have tended to ignore the frictional effects associated with airflow across the envelope of the acoustic cavity (e.g., resistive vents). Since such leakage through the cavity envelope is best expressed with a power law dependence on the pressure, standard Fourier techniques that rely on linearity cannot be used. In this article, the theory relevant to nonlinear leakage is developed and equations presented. Potential applications of the theory to techniques for quantifying the leakage of buildings are presented. Experimental results from pressure decays in a full-scale test structure are presented and the leakage so measured is compared with independent measurements to demonstrate the technique.
Arrival time and pulse width of acoustic pulses in a turbulent ocean
Authors: Tarng J. H. , Wang L. K. , Yang C. C. , McDaniel S. T.
Published: October 2005

Pulse distortion in a turbulent ocean is investigated using the temporal moment method. The first- and second-order temporal moments are related to the pulse arrival time and pulse width, respectively. Without dispersion in the ocean, the pulse is expected to be delayed and broadened owing to sound-speed fluctuations. The effects of the vertical sound-speed profile are included. To simplify the computations, the turbulent ocean is assumed to be statistically homogeneous and isotropic, and to follow a Gaussian correlation function. In computing the temporal moments, the coefficients in a power series expansion of the two-frequency mutual coherence function have to be evaluated in terms of the relative difference between two wavenumbers. A bilinear sound-speed profile is used. The propagation range is limited under the assumption that the ray trajectory does not pass the depth of the minimum sound speed. Numerical results show that the effects of random scattering on the arrival time are negligibly small. However, random scattering will significantly broaden the pulse, especially when the range is large.
Sound attenuation through trees: Measurements and models
Authors: Price Margaret A. , Attenborough Keith , Heap Nicholas W.
Published: October 2005

Measurements obtained at three British woodlands for the frequency-dependent attenuation of broadband sound with distance under neutral atmospheric conditions are compared with the predictions of a model obtained by summing the separate contributions of the ground, the trunks and branches, and the foliage. The two latter contributions are predicted by an empirically modified multiple scattering approach. The principal features of the measured spectra, viz., the low-frequency peak in excess attenuation below 500 Hz and a gradual increase of attenuation with frequency above 1 kHz, are predicted in a tolerable fashion by the composite model, as are the observed differences in acoustic propagation in the three different woodland areas.
Equilibrium shape and location of a liquid drop acoustically positioned in a resonant rectangular chamber
Authors: Jackson H. W. , Barmatz M. , Shipley C.
Published: October 2005

The effect of a standing wave field in a rectangular chamber on the shape and location of an acoustically positioned drop or bubble is calculated. The sample deformation and equilibrium position are obtained from an analysis of the spherical harmonic projections of the total surface stress tensor. The method of calculation relies on the assumed condition that the sample is only slightly distorted from a spherical form. The equilibrium location of a levitated drop is combined with a formula introduced by Hasegawa to calculate the ka dependence of the radiation force function. The present theory is valid for large as well as small ka values. Calculations in the small ka limit agree with previous theories and experimental results. Examples are presented for nonplane-wave modes as well as plane-wave rectangular modes.
Sound in a layered fine fiber porous material with finite frame stiffness
Authors: Lambert Robert F.
Published: October 2005

This study reports some comparisons between predicted and measured sound propagation characteristics in a layered fiber, highly porous, air-saturated material having a structural frame that exhibits finite stiffness. It compares theoretical attenuation and phase speeds at several frequencies over a range of stiffness parameters varying from a ‘‘stiff’’ frame limit through a transition region and into a ‘‘soft’’ frame limit. Measured values of attenuation and phase speed in several samples of Kevlar 29 mounted in a small tube are compared to the theoretical predictions. These samples did not qualify for a soft frame limit but the comparisons are favorable in the stiffer frames regimes. Finally, comparisons are made between equivalent single-wave propagation and exact numerical solutions to the coupled equations of motion. Several comparisons between predicted and measured surface admittance characteristics of two bulk samples of Kevlar having quite different frame stiffness properties also are made. These comparisons show good agreement over a wide range of frequencies.
Radiation and scattering of acoustic waves from elastic solids and shells using the boundary element method
Authors: Seybert A. F. , Wu T. W. , Wu X. F.
Published: October 2005

In this article the radiation and scattering of sound from elastic bodies of arbitrary shape are examined. The coupled acoustic/elastic boundary value problem is reformulated into a pair of integral equations, one for the acoustic domain (the host fluid) and one for the elastic body. Both of these integral equations are valid at the interface (the body’s surface) between the elastic body and the fluid. The integral equations are coupled by continuity conditions at the interface. The integral equations are reduced to numerical form using quadratic isoparametric elements and solved simultaneously to determine the unknown pressure and displacements on the interface. Field solutions are obtained by quadrature of the data on the interface. The integral equation method is tested for several radiation and scattering problems in which the elastic body is either a hollow or solid sphere of various material compositions.
On the transient sound radiation from a planar source with time-varying extent
Authors: Levine Harold
Published: October 2005

An acoustical type of excitation, resulting from a planar source domain that appears instantaneously and steadily grows to a permanent finite size, is studied on the basis of linear theory and the particular assumptions: (i) that a uniform normal velocity prevails over the source; and (ii) that the velocity vanishes elsewhere in its plane. The total energy radiated by such sources during their entire transient phase is expressed in general terms and calculated explicitly for the representatives that eventually assume a circular or square shape. The energy varies in a continuous overall manner as a function of the speed that characterizes the expanding source area and, moreover, remains constant above the sonic speed level; a discontinuity in slope of the energy curve occurs at this level.
A note on the durations of fricatives in American English
Authors: Crystal Thomas H. , House Arthur S.
Published: October 2005

The recent observations of Baum and Blumstein on the durations of word-initial fricatives in citation form [J. Acoust. Soc. Am. 82, 1073–1077 (1987)] are augmented with additional data on word-initial and word-final fricatives in connected speech. In general, these data support their findings that voiceless fricatives are longer than voiced fricatives and that the distributions of the two classes overlap considerably. The distinction is more pronounced if the fricatives are first separated on the basis of their position in a word, whether word-final tokens are prepausal, and stress characteristic. The data suggest also that fricatives in connected speech are shorter than those in citation form.
Parametric study of a laser-generated thermoacoustic signal
Authors: Gonzalez Luis J. , Busch-Vishniac Ilene J.
Published: October 2005

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.
Occurrence of transient cavitation in pulsed sawtooth ultrasonic fields
Authors: Aymé Eveline J. , Carstensen Edwin L.
Published: October 2005

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.
The role of pinna movement for the localization of vertical and horizontal wire obstacles in the greater horseshoe bat, R
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Authors: Mogdans Joachim , Ostwald Joachim , Schnitzler Hans-Ulrich
Published: October 2005

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.
Effect of transient signal length on cross-correlation functions in a room
Authors: Yanagawa Hirofumi , Yamasaki Yoshio , Itow Takeshi
Published: October 2005

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.
Broadband acoustic holography reconstruction from acoustic intensity measurements. I: Principle of the method
Authors: Loyau Thierry , Pascal Jean-Claude , Gaillard Paul
Published: October 2005

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.
Real-time visualization of acoustic wave fronts by using a two-dimensional microphone array
Authors: Hiranaka Yukio , Nishii Osamu , Genma Takayuki , Yamasaki Hiro
Published: October 2005

This article describes a real-time visualization system for sound fields. The system includes a two-dimensional microphone array (8×8), which eliminates the need for mechanically scanning the microphone and enables real-time processing. Three methods are tested for drawing interpolated images of sound fields from the sparse sampling points. A frequency-detection circuit is introduced to show the direction of sound propagation stroboscopically. Superposition of visualized sound wave fronts on the video picture of the field helps one to understand the sound fields present.
Estimates of two-point, broadband temporal coherence using a z-transform technique
Authors: Feuillade C. , Kinney W. A.
Published: October 2005

Values of broadband coherence versus time delay are presented for two horizontally separated receivers in water overlying a rigid bottom. These values are given for different source azimuth angles (from broadside to endfire) and for (a) surface-bottom (SB) paths, (b) bottom-surface (BS) paths, and (c) a combination of SB and bottom-reflected (B) paths. The acoustic wavelength band considered is the passband from 0.2–1.0 m. The water depth and range are both 5 km. The source and receivers are all at 200 m depth, with the receivers separated by 25 m. The ocean bottom is assumed to be rigid and flat. Scattering from the ocean surface is modeled using the time-domain, facet-ensemble method [H. Medwin, J. Acoust. Soc. Am. 69, 1060–1064 (1981); C. S. Clay and W. A. Kinney, J. Acoust. Soc. Am. 83, 2126–2133 (1988)] applied to a long-crested wave model of the ocean surface using actual wave-height measurements with an rms value of 1 m. A z-transform algorithm (suggested by C. S. Clay) is used to perform broadband filtering and to compute coherence. Results demonstrate how signals that arrive endfire via SB paths possess greater coherence (with values near 0.8) than signals that arrive via BS paths (values near 0). This is because the SB path involves scattering off areas on the ocean surface that are close together and physically similar.
Interpretation of the three-dimensional sound fields scattered by submerged elastic shells and rigid spheroidal bodies
Authors: Gaunaurd G. C. , Werby M. F.
Published: October 2005

The direct scattering problem associated with submerged spheroidal targets at frequencies within their resonance regime is studied. The incident waves are plane and continuous, and the composition of the spheroid can be either impenetrable or penetrable. In the impenetrable case, the body is assumed rigid. In the penetrable case, the target is an elastic shell, whose motion is governed by the exact three-dimensional equations of linear elastodynamics. The aspect ratio of the spheroids takes on values from L/D=1.5–30. The method used in the calculations is the extended boundary condition (EBC) or T-matrix method. The target’s form function or scattering angular pattern in the farfield versus monostatic variable angles of incidence at fixed frequencies (i.e., monostatic angular plots), or versus frequency, at fixed directions of observation (i.e., backscattering responses), is displayed. The graphs exhibit the versatility of the EBC method, particularly in cases, such as for the elastic shell, in which analytic solutions are not possible. The case of an elastic shell is considerably more difficult than that of any impenetrable or solid elastic spheroid. The aspect ratio analyzed here for a shell is at the current upper limit of performance of the computational method used in our analysis. Various resonance effects in the displayed plots are studied, particularly the resonance isolation process present in the backscattering responses and the connection to combinations of Legendre functions observable in the angular plots. The relative values of the creeping-wave levels and those due to specular reflections are also compared. For very elongated spheroids, the creeping wave levels seem to be stronger(!). Calculated predictions are displayed, and an explanation of this interesting situation is offered.
Ultrasonic backscatter from flowing whole blood. I: Dependence on shear rate and hematocrit
Authors: Yuan Y. W. , Shung K. K.
Published: October 2005

Previous results show that ultrasonic backscatter from red blood cells (RBCs) suspended in saline is a function of hematocrit and frequency and that it can be affected by flow disturbance. The experimental data agree well with the theories. In the present article, results on ultrasonic backscatter from flowing whole blood are reported. Studies have been conducted on porcine, bovine, and human blood. Ultrasonic backscatter of flowing whole blood differs from that of RBC suspensions in that it is shear-rate dependent, which means that it is a function of spatial position of the blood in the flow conduit. Moreover, the results indicate that it is also species dependent. This behavior can be readily understood when red cell aggregation is considered.
On the cut-on frequencies of a large round duct with azimuthal as well as radial partitions
Authors: Munjal M. L.
Published: October 2005

This letter deals with a three-dimensional analysis of circular sectors and annular segments resulting from the partitioning of a round (cylindrical) duct for use in an active noise control system. The relevant frequency equations are derived for stationary medium and solved numerically to arrive at the cut-on frequencies of the first few modes. The resultant table indicates among other things that azimuthal partitioning does not raise the cutoff frequency (the smallest cut-on frequency) beyond a particular value, and that radial partitioning is counterproductive in that respect.
Sound propagation through random currents using parabolic approximations
Authors: Brent R. I. , Jacobson M. J. , Siegmann W. L.
Published: October 2005

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.
Acoustic waves generated by a point source in a sloping fluid layer
Authors: Pao Yih-Hsing , Ziegler Franz , Wang Yi-Sun
Published: October 2005

The propagation of acoustic waves generated by a point source in a wedge-shaped fluid layer on top of a semi-infinite space is analyzed by applying the generalized ray method. The horizontal top surface is assumed at a constant pressure and the lower surface of the wedge is in contact with another large body of fluid. Numerical results are presented for the case of a slow wave-speed bottom and a fast wave-speed bottom with three different dipping angles (0°, 5°, 10°) at various locations near a center of explosion with a step-time function. The diffraction from the apex of the wedge is neglected in this otherwise exact analysis.
Bispectrum of ship-radiated noise
Authors: Hinich Melvin J. , Marandino Davide , Sullivan Edmund J.
Published: October 2005

The bispectrum of ship-radiated noise is estimated. The noise was received on a towed array being towed by the same ship that served as the noise source. The array was beamformed such that the forward endfire beam pointed toward the towing platform and the broadside beam sampled the environment without the radiated noise of the ship. The results show that there exist frequency-dependent bispectral components in the ship’s radiated noise, whereas the ambient noise does not contain any significant bispectral components. Since the existence of a nonzero frequency-dependent bispectrum indicates the existence of nonlinear components in the noise-generating mechanism, it is concluded that the radiated noise of the towing platform contains such nonlinear mechanisms. Therefore, the bispectrum could be used to indicate the existence of such noise sources as would normally be hidden in the background noise when the usual spectral estimation procedures are applied.
Nonlinear forced vibrations of shallow shells on regular polygonal bases
Authors: Coleby J. R. , Mazumdar J.
Published: October 2005

The nonlinear, large amplitude vibrations of elastic, shallow shells when subjected to transient pressure loading are analyzed in a relatively simple manner. The isoamplitude contour lines approach is used to derive the basic equations for shallow shell vibrations. The coupled system of governing equations thus obtained is solved for shells of regular polygonal planform with various types of dynamic loading. Also, an equivalent analysis in which Berger’s approximation is used is presented and a comparison is made of the results obtained by both methods. Some comparison is also made with previously obtained results, as available in the literature. All details are explained by graphs.
On the energetics of axially moving continua
Authors: Wickert J. A. , Mote C. D.
Published: October 2005

The total mechanical energy associated with an axially moving string or beam that travels between two supports is not constant. In general, the total energy varies at twice the frequency of free oscillations. The time-dependent component of the energy derives from energy flux through the supports, and the convective velocity of material particles in the continuum renders the net flux nonzero. Expressions for the temporal variation of the energy associated with the string and beam models are derived and analyzed. For single-mode free response of the traveling string, the total energy is constant at particular transport speeds.
Resonance scattering in suspensions
Authors: Hay Alex E. , Schaafsma Arjen S.
Published: October 2005

Measured and theoretical total cross sections for aqueous suspensions of lead glass and polystyrene beads are presented. Attenuation is measured from 1 to 100 MHz in a recirculating suspension circuit using a swept-frequency system and broadband transducer pairs. The theoretical calculations employ the phase shift formalism and the coherent removal of a rigid scatterer background. Good agreement between theory and experiment is obtained for both types of particle, and departures from the rigid sphere cross section are due to resonance scattering. The resonance features in the glass bead cross sections are dominated by broad Rayleigh wave resonances, with frequencies close to those given by the in vacuo free-body resonance condition, and represent departures from the rigid sphere cross section of, at most, 25%. In contrast, the polystyrene bead cross sections are dominated by narrow resonance features with maximum amplitudes up to five times greater than the geometric scattering cross section. It is shown that these resonances, which we call giant resonances, occur at frequencies given by an immersed free-body resonance condition that is derived by assuming the existence of wave trapping in the fluid at the surface of the sphere. This condition yields frequencies that are wholly real, consistent with the observed narrow resonance widths, and leads to an approximate expression for the resonance amplitudes that is in good agreement with the exact calculations. The meridional wave phase speeds are consistent in the appropriate limit with Stonely waves. The giant resonances cease to exist if the meridional wave phase speed approaches the speed of sound in the ambient fluid.