bluuebunny/crossref_metadata_2025 huggingface dataset:
Censor’s acoustical Doppler effect analysis—Is it a valid method?
Authors: Piquette Jean C. , Van Buren A. L. , Rogers Peter H.
Published: October 2005

In the article, ‘‘Acoustical Doppler effect analysis—Is it a valid method?’’ [J. Acoust. Soc. Am. 83, XXX–XXX (1988)], Censor considers the problem of scattering in the presence of moving objects under conditions of space- and time-dependent moving media. He considers this situation in the context of a generalized linear wave equation. This equation predicts the generation of Doppler-type spectral components at frequencies that are equal to (i) the sum of the frequencies of the primary waves, (ii) the difference of the frequencies of the primary waves, and (iii) harmonics of these sum-and-difference frequencies. However, since the nonlinear wave equation also predicts scattered spectral components at these same frequencies, and since those predicted by the nonlinear theory are usually much stronger than those predicted by Censor’s theory, the generalized linear wave equation used by Censor is generally inadequate for accurately predicting the amplitudes of the spectral components of interest. However, a limited regime is identified in which the spectral components predicted by Censor’s theory can dominate those predicted by nonlinear theory.
Earphones in audiometry
Authors: Zwislocki Jozef , Kruger Barbara , Miller James D. , Niemoeller Arthur F. , Shaw Edgar A. , Studebaker Gerald
Published: October 2005

The advantages and disadvantages of three types of earphones for audiometric testing are discussed. Supraaural earphones continue to be recommended for this purpose, in preference to circumaural and insert types.
An investigation of voided PVdF after exposure to high-pressure pulses
Authors: Leaver P. , Cunningham Michael J.
Published: October 2005

The effect of high-pressure (0–75 MPa) pulses on the piezoelectric properties of voided PVdF film has been investigated. The SEM micrographs show that microvoids still exist in the material after exposure to many such pressure pulses. The measured decrease in the piezoelectric coefficient reported by other workers would appear to require a new explanation.
Transducer array excitations for optimum difference patterns
Authors: McNamara Derek A.
Published: October 2005

Exact synthesis techniques for arrays of transducers providing difference patterns are reported. These methods utilize the class of functions known as the Zolotarev polynomials. They are the difference analogs of the sum array synthesis procedures based on the Chebyshev polynomials.
Active cancellation of noise in a liquid-filled pipe using an adaptive filter
Authors: Culbreth William G. , Hendricks Eric W. , Hansen R. J.
Published: October 2005

An experimental study of active attenuation of sound in a liquid-filled pipe is reported. The pipe was connected to a ‘‘noise’’ source at one end and opened into a large liquid reservoir at the other. A sound source for active cancellation purposes was located midway between the two extremities. A cancellation signal to drive the active source was generated by a digital, adaptive filter from hydrophones located in the duct and reservoir. The reduction in noise level was measured at the exit of the pipe into the reservoir and at selected locations in the reservoir. Sound attenuations in the 20-dB range were observed.
Theoretical estimates of sound scattering by atmospheric turbulence
Authors: Baikalova R. A. , Krekov G. M. , Shamanaeva L. G.
Published: October 2005

The coefficients of sound scattered by the temperature and wind fluctuations and common normalized scattering phase functions are computed using the von Karman three-dimensional spectrum of temperature fluctuations and the von Karman three-dimensional energy spectrum that enables one to take into account the outer scale of atmospheric turbulence. It is shown that both scattering coefficients have a quadratic frequency dependence and 1.67 power dependence upon the outer scale of turbulence. At the same time, the common scattering cross section is proportional to the cube root of the sound frequency that agrees with the previously obtained results. The obtained results are in a good agreement with the experimental data.
Transient Scholte wave transmission along rough liquid–solid interfaces
Authors: Chamuel Jacques R. , Brooke Gary H.
Published: October 2005

Transmission characteristics of transient Scholte waves along periodic and random liquid–solid interfaces are demonstrated using laboratory ultrasonic models. These characteristics indicate that, for periodic interfaces, the transmitted Scholte wave is composed of an attenuated main pulse, which arrives first, followed by substantial energy at the Bragg frequency, which is delayed and spread over a wide time window. Random topographic variations in the liquid–solid interface eliminate the transmission of the late-arriving components. The experiments are limited to a water ‘‘half-space’’ over a high-speed solid half-space, in which case, most of the Scholte wave energy is in the water. The Scholte wavelength is comparable to the horizontal spatial wavelength in the surface but is much greater than the vertical scale of the spatial variations. Results from composite interfaces formed by placing thin parallel scatterers on a plane solid surface and from corrugated interfaces formed by directly machining grooves and ridges in the solid are presented. Field data on transient Scholte wave propagation in the shallow waters of Barrow Strait of the Canadian Arctic are also described. The field data have some similar characteristics to that obtained from the ultrasonic models, which may indicate that the propagation in Barrow Strait is strongly influenced by the bottom topography of the region.
Time domain signal transmission and source location in a waveguide: Matched filter and deconvolution experiments
Authors: Clay C. S. , Li Saimu
Published: October 2005

The experiments were made in an ideal air waveguide having Sheetrock (hard) boundaries. Transmissions of a signal were from a source to a pair of receivers. Matched filter and deconvolution procedures were tested. Matched filters were computed for transmissions from a set of trial source locations to the receivers. The trial matched filters were then applied to the signals. The filtered signals were cross correlated. A map of cross-correlation absolute maxima for trial source locations gave the actual source location. Many smaller maxima indicated false locations. For the second method, the signals were deconvolved with estimates of the impulse transmission from trial locations. At the actual source location, deconvolution operations gave a diverging oscillatory remainder. The oscillations had a higher frequency than the signal. It was possible to low-pass filter the deconvolved signals and recover good replicas of the transmitted signal. The map of cross correlations of the deconvolved and filtered signals gave the source location. The deconvolution–low-pass filter method gave fewer and smaller indications of false locations than the matched filter method. However, the matched filter method was more tolerant of errors in the estimates of the impulse response.
Critical behavior of the ultrasonic attenuation for the binary mixture: Methanol and cyclohexane
Authors: Fast Steven J. , Yun S. S.
Published: October 2005

The experimental value of the slope of α/f 2 vs f −1.06 of the ultrasonic attenuation for the critical mixture is compared to the calculated value based on the dynamic scaling theory at the critical temperature. The values of α/f 2 vs f −1.06 yield a straight line as predicted by theory. The adiabatic coupling constant g is calculated and compared to the experimental value. The experimental values of α/αc for methanol and cyclohexane are compared to the scaling function F(ω*) and to the values of α/αc for 3He and Xe.
Reflection and transmission of normally incident ultrasonic waves on periodic solid–liquid interfaces
Authors: Mampaert K. , Leroy O.
Published: October 2005

It is verified experimentally that when a broadband beam interacts with periodically rough boundaries at normal incidence, the spectrum of the reflected beam contains several minima that are characteristics of the various parameters of the interface. An analytical approach to this problem was made by Claeys and Leroy [Rev. Cethedec 72, 183–193 (1982)] for the case of a liquid–solid boundary. In the present work the theory is extended for waves incident from the solid into the liquid. The frequency dependence of the reflection coefficient is calculated for various periodic structures, from which a correlation between the extrema of the spectrum and surface type waves, as well in the solid and the liquid, is discussed.
Sound power emission in reverberation chambers
Authors: Maa Dah-You
Published: October 2005

Sound power emission of a simple source in a reverberation chamber is derived from the normal mode theory and compared to that in free space. Both pure-tone and noise sources are considered. The acoustic impedance of the sound source itself is deemed important in its power emission and incorporated into the analysis. The acoustic impedance presented to the source by the sound field produced in the chamber varies significantly from point to point, and this leads to the large variability of the power output of the source in the room. But the average obtained over the whole room approximates well the sound power produced in free space, provided that the source impedance is large compared to the field impedance and that the frequency is high enough so that the normal modes overlap. A statistical formula is derived for the power emission as a function of the space coordinates in the room. It is found that the power emission is a maximum on the boundary, and undulates about the free-field value when the source is moved toward the center of the room. The average power emission is less than the free-field value if the averaging avoids the high-power region near the boundaries, as is usually the case. The difference is derived that seems to explain the earlier results of sound power measurements.
Multibeam imaging using spatially variant insonification
Authors: Jaffe Jules S. , Cassereau Philippe M.
Published: October 2005

The simultaneous transmission of a number of specially coded waveforms can provide a number of substantial advantages for active sonar imaging. Two of the possible advantages are increased imaging speed and better sidelobe rejection. In order to maintain the integrity of the individual, but simultaneously transmitted, beams, the signals must possess specific mathematical properties. A narrow autocorrelation function and a small cross-correlation function are desirable in order to insure both accurate range resolution and rejection of neighboring beams. It is demonstrated that this design criterion is identical to that encountered in multiaccess, spread spectrum, communication systems. The time-bandwidth properties of the system therefore limit the simultaneous requirement of decorrelatable beams and good range resolution. As a specific implementation of the technique, a frequency hopping code is presented. The performance of this code is examined and it is demonstrated that this code is nearly optimal with respect to the above criterion. Various configurations of transducers are considered that specifically exploit the properties of spatially variant insonification (SVI). The principles of multibeam sonar imaging systems using spatially variant insonification are illustrated by constructing several examples of active sonar systems whose performances are superior over traditional designs.
Minimum bandwidth interpolation of real discrete data
Authors: Birdsall Theodore G. , Bold Gary E. J.
Published: October 2005

A DFT-spectrum-preserving transformation from one finite set of real numbers to a larger set of real numbers is developed. This transformation is completely in the time domain. Its convolution kernel, psinc(x;P), is analogous to the sinc(x) function familiar in Fourier transform work with continuous waveforms. The application to generation of periodic signals with specified bandlimited spectra is illustrated, as is interpolation using a mixture of time-domain and radix-2 fast Fourier transform (FFT) processing.
The estimation of target motion parameters from cpa time measurements in a field of acoustic sensors
Authors: Dommermuth F. M.
Published: October 2005

The flight parameters of a nonmaneuvering aircraft can be determined from the closest points of approach (cpa) time registrations in a field of acoustic sensors. In plane geometry, and with four sensors, the problem has a (nearly) closed-form solution. Monte Carlo simulation is applied to demonstrate that the solution behaves in a stable manner against a deviation from the hypothesis of zero target height, in the order of the distance between sensors, as long as the target velocity is not too high. Application to real data has demonstrated the feasibility of the procedure.
Generation and detection of high-order harmonics in liquids using a scanning acoustic microscope
Authors: Germain L. , Cheeke J. D. N.
Published: October 2005

The nonlinear generation of harmonics by high-power focused acoustic beams in liquids has been investigated. A transmission mode acoustic microscope using focal plane detection has been used for high-harmonic signal sensitivity. Detection of up to the 14th harmonic in ethanol has been achieved at an emission frequency of 15 MHz. Measurements show that signal in all harmonics tends to saturate at a very high emitted power. At lower power, harmonics varied as Pn1, where P1 is the emitted power and n the harmonic number. Resolution improvement of the acoustic microscope by receiving at harmonic signals has also been demonstrated. The resolution has been shown to increase as (n)1/2 for reception at the nth harmonic, in good agreement with focused Gaussian beam theory. A nonlinear resolution improvement by a factor of 3 has been obtained.
Comparison of perturbation theories for rough-surface scattering
Authors: Jackson Darrell R. , Winebrenner Dale P. , Ishimaru Akira
Published: October 2005

Rayleigh–Rice perturbation theory is compared with the more rigorously derived perturbation theory based on the extinction theorem (or extended boundary condition) for the case of Dirichlet boundary conditions. Numerical calculations for a sinusoidal surface profile show that the two theories give identical results when carried out to high order. This is true even when the two series do not seem to converge numerically. Numerical convergence of the two series is found in several cases, including some cases in which the Rayleigh hypothesis is invalid. For surfaces of arbitrary shape, the two perturbation series appear superficially to differ at third and higher order. It is shown, however, that a reciprocity transformation of one series makes it identical to the other through fifth order. Finally, it is shown that reciprocity holds in both perturbation theories, establishing analytically the equivalence of the two theories at least through fifth order. These results are surprising given the limited regime of validity for the Rayleigh hypothesis compared with the extinction theorem. They are useful in that they justify the use of perturbation formulas obtained from the Rayleigh hypothesis in lieu of the more complicated formulas obtained from the extinction theorem. While these results do not establish the identity of the two perturbation methods to all orders or settle questions as to their convergence, they do provide some theoretical clues to the nature of these problems.
Quantitative evaluation of microfracture due to disbonding by waveform analysis of acoustic emission
Authors: Yuyama S. , Imanaka T. , Ohtsu M.
Published: October 2005

Surface motions due to a disbonding of a stainless overlay welded on base metal of a pressure vessel have been measured by the use of a commercially available flat-frequency displacement transducer. The experimental result showed that a buried tensile crack (penny-shaped crack) can be generated by hydrogen-induced disbonding of stainless weld overlay from base metal. Acoustic emission (AE) was found to be very sensitive and effective to monitor the disbonding. Some tens of AE events could be located by using two meaningful Δt values. The detected waveforms due to the disbonding exhibited interesting variation as a function of the distance between the source epicenter and the transducer location. On the basis of the theory of elastodynamics and dislocation models, simulation analysis was made for surface motions due to a penny-shaped crack parallel to the stress-free surface in a half-space. Simulated waveforms were obtained as a function of the distance between the epicenter and the observation position. Comparison of the detected and simulated waveforms indicated remarkable agreement in the early time response. This agreement demonstrates the applicability of the transducer and the present simulation analysis to quantitative waveform analysis relating to fundamental AE work. It is shown that quantitative analysis of microfracture due to the disbonding can be readily made by comparison of experimentally measured surface displacements and theoretically calculated surface motions.
Evaluation of vertical vibration given to the human foot
Authors: Miwa Toshisuke
Published: October 2005

The effects of acceleration amplitudes and frequencies of vertical foot vibration on mechanical and sensation responses were studied in two sets of experiments. The first experiments determined the mechanical characteristics of the foot in three seated subjects at frequencies between 5 and 1000 Hz, in terms of the driving point mechanical impedances and acceleration transmission ratios between the foot and lower leg. In the second set of experiments, sensation scales for foot vibrations were determined in ten seated subjects at octave center frequencies between 8 and 400 Hz, which involved equal sensations of continuous and impulsive motions, sensation magnitudes, and rating of five successive categories of sinusoidal motion. Contours of mechanical and sensational responses are presented. Using the results obtained, a foot response meter was made and used in a field survey to evaluate foot vibration.
Acoustical Doppler effect analysis—Is it a valid method?
Authors: Censor Dan
Published: October 2005

The Doppler effect approach is a powerful tool used in various areas of physics to analyze motion in a wave field, by observing the frequency shifts of scattered waves. In acoustics, Doppler effect analysis is used for diagnostics in biomedical systems and for industrial applications, e.g., in cases where scatterers are present in moving fluids. The theoretical models used to analyze such systems usually ignore the fact that the moving ambient medium might produce effects of the same order of magnitude as the scatterers themselves. It has even been argued that in certain circumstances such effects should completely cancel the Doppler frequency shifts. A model is developed here that contributes to our understanding of the scattering in the presence of moving objects and space- and time-dependent moving media. The model is restricted to irrotational flows, neglects velocity effects except of the first order in the Mach number v/c, and assumes slow variations in the ambient medium. These restrictions facilitate the analytical discussion of specific canonical problems. The present study indicates that Doppler effects can be produced by moving scatterers in a medium at rest, scatterers at rest in a moving medium, and in configurations in which combined motion of scatterers and media take place. The Doppler effects are of the same order of magnitude in all cases. This vindicates the simple models used for research and applications, which assume that the moving objects produce Doppler effects but neglect the flow of the surrounding medium.
The scattering of ultrasonic waves by multiphase polycrystals
Authors: Hirsekorn Sigrun
Published: October 2005

The theory of ultrasonic propagation in single-phase polycrystals presented in previous articles [J. Acoust. Soc. Am. 72, 1021–1031 (1982); 73, 1160–1163 (1983)] is generalized to calculate the scattering coefficients and phase and group velocities of plane compressional and shear waves in multiphase polycrystals. The analytical calculation was done for macroscopically isotropic materials with phases of cubic, hexagonal, or orthorhombic single-crystal symmetry in second-order perturbation theory using the assumption that the relative mean quadratic deviation of the wavenumbers in the polycrystal considered from its homogeneous isotropic approximation is small. Numerical evaluation is carried out for a two-phase material of α- and γ-Fe.
On the nonobservance of nonspecular bounded beam reflection effects of Lamb modes
Authors: de Billy M. , Molinero I.
Published: October 2005

Reflection and transmission effects are investigated for angles of excitation of Lamb waves that are near the longitudinal critical angle. It will be shown that, for this particular angle, the coupling at the interfaces liquid/solid/liquid is such that the leaky-surface-wave-radiation effect does not occur because of the weak coupling between the two media. This result affects only the symmetrical Lamb modes Si (i≠0).
A reanalysis of the acoustic scattering from elastic spheroids
Authors: Hackman Roger H. , Sammelmann Gary S. , Williams Kevin L. , Trivett D. H.
Published: October 2005

The elastic response of fluid-loaded, elastic spheroids to an end-on incident acoustic wave is analyzed for a variety of aspect ratios and material properties. The focus of this analysis is the nature of the elastic excitations of the target, and, to a lesser extent, the nature of the inelastic background. It is concluded that the low kL/2, resonant response of the target is closely related to a bar wave, propagating at nearly one and one-half times the shear speed at low frequencies and that the rigid body solution with recoil is the appropriate background choice for all materials. Bistatic scattering calculations are also studied, and it is concluded that the lobe structure of the elastically reradiated signal cannot be used to characterize a resonance without a priori knowledge of the target. The results contradict recent, but more phenomenologically oriented, studies.
Reflection characteristics of an elastic slab containing a periodic array of circular elastic cylinders: P and S
V wave analysis
Authors: Lakhtakia Akhlesh , Varadan Vasundara V. , Varadan Vijay K.
Published: October 2005

The reflection and transmission characteristics of circular elastic cylinders arranged periodically in an elastic slab are examined. A simple approach synthesized from Fourier–Bessel expansions and the T-matrix method has been used for the analysis of a two-dimensional problem involving P and SV waves. The computed results are of importance in grating theory as well as in noise control, although the procedure given is restricted to only the low-frequency regime.
Probability density functions of sums of sinusoidal waves having nonuniform random phases and random numbers of multipaths
Authors: Barakat Richard
Published: October 2005

The purpose of this article is to study the first-order statistics (i.e., probability density functions and moments) of finite sums of cosines and of sines, each having nonuniformly distributed random phases governed by a von Mises probability density function. The number of sinusoids N is, first, taken to be deterministic, but arbitrary, and, second, taken to be a discrete random variable governed by a negative binomial distribution (which includes the Poisson distribution as a special case). Since the phase probability density functions are nonuniform, the probability density functions of the cosine sum and the sine sum are different. The probability density functions of these cosine and sine sums are evaluated using Fourier series expansions whose Fourier coefficients are sampled values of the corresponding characteristic functions. Representative numerical calculations have been carried out to illustrate the general features. The corresponding moments have also been evaluated. Finally, the behavior of the probability density functions and moments when N approaches infinity in the deterministic situation and 〈N〉 approaches infinity in the random situation is investigated, the former involving the theory of stable probability density functions, the latter involving the theory of infinitely divisible probability density functions.
Direction of arrival estimation by eigenstructure methods with imperfect spatial coherence of wave fronts
Authors: Paulraj A. , Kailath T.
Published: October 2005

Eigenstructure/subspace methods for direction of arrival estimation are only applicable when each wave front contributes a rank one component to the array covariance. This implies that the wave fronts need to have perfect spatial coherence. In several practical situations where the wave fronts may only have partial spatial coherence, eigenstructure algorithms show poor performance such as overestimation of the number of sources, bias, and reduced accuracy and resolution in estimating the directions of arrival. In this article, the performance degradation due to partial spatial coherence is studied and a new approach is proposed that exploits the underlying coherence model to yield asymptotically exact estimates. For finite data, this method provides improved results only when the number of snapshots exceeds a certain threshold. Results of computer simulations are also presented.
Simulation of auditory–neural transduction: Further studies
Authors: Meddis Ray
Published: October 2005

A computational model of mechanical to neural transduction at the hair cell–auditory-nerve synapse is presented. It produces a stream of events (spikes) that are precisely located in time in response to an arbitrary stimulus and is intended for use as an input to automatic speech recognition systems as well as a contribution to the theory of the origin of auditory-nerve spike activity. The behavior of the model is compared to data from animal studies in the following tests: (a) rate-intensity functions for adapted and unadapted responding; (b) two-component short-term adaptation; (c) frequency-limited phase locking of events; (d) additivity of responding following stimulus-intensity increases and decreases; (e) recovery of spontaneous activity following stimulus offset; and (f) recovery of ability to respond to a second stimulus following offset of a first stimulus. The behavior of the model compares well with empirical data but discrepancies in tests (d) and (f) point to the need for further development. Additional functions that have been successfully simulated in previous tests include realistic interspike-interval histograms for silence and intense sinusoidal stimuli, realistic poststimulus period histograms at various intensities and nonmonotonic functions relating incremental and decremental responses to background stimulus intensity. The model is computationally convenient and well suited to use in automatic recognition devices that use models of the peripheral auditory system as input devices. It is particularly well suited to devices that require stimulus phase information to be preserved at low frequencies.
Three-dimensional acoustic waves in the ear canal and their interaction with the tympanic membrane
Authors: Rabbitt R. D. , Holmes M. H.
Published: October 2005

The long and slender geometry of the ear canal supports an infinite number of cross-sectional acoustic modes. The lower mode(s) travel along the length of the ear canal, while the higher modes are trapped near the ends of the canal. Many of these waves are introduced as a result of the complex vibrational shape of the eardrum. A three-dimensional mathematical model of the ear canal is formulated that includes this acoustic interaction. The coupled system is solved using matched asymptotic expansions that take advantage of the small slenderness ratio. This solution in the ear canal is in the form of a series of modes, the first being the plane-wave solution. As an illustrative example, the analysis is applied to a geometry that partially represents the ear canal and eardrum of a cat. The results indicate that the plane-wave solution is supplemented by multidimensional trapped modes at low frequencies and by a limited number of traveling waves at high frequencies. The magnitude of these higher modes generally increases with frequency and can significantly influence the acoustic coupling of the ear.
Masking patterns in the bullfrog (R
a
n
a c
a
t
e
s
b
e
i
a
n
a). I: Behavioral effects
Authors: Simmons Andrea Megela
Published: October 2005

A psychophysical technique based on reflex modification was used to measure masked auditory thresholds in the bullfrog (Rana catesbeiana). Masked thresholds were converted to critical ratios to describe the frequency selectivity of the bullfrog’s hearing. The bullfrog’s critical ratio function is complex. At low frequencies (100–600 Hz), it increases gradually with tone frequency at a rate of about 4 dB/octave. At high frequencies (1000–2500 Hz), the rate of increase with tone frequency is steeper (9 dB/octave). Critical ratios are lowest at frequencies around 1000 Hz (about 18 dB). Unlike effects previously reported in another anuran species, the green treefrog, the bullfrog’s critical ratio function is not parallel to its pure-tone audiogram. Moreover, the relationship of the bullfrog’s critical ratio function to the spectral composition of its species-specific vocalizations is not as compelling as in the green treefrog.
The shape of the ear’s temporal window
Authors: Moore Brian C. J. , Glasberg Brian R. , Plack C. J. , Biswas A. K.
Published: October 2005

This article examines the idea that the temporal resolution of the auditory system can be modeled using a temporal window (an intensity weighting function) analogous to the auditory filter measured in the frequency domain. To estimate the shape of the hypothetical temporal window, threshold was measured for a brief sinusoidal signal presented in a temporal gap between two bursts of noise. The duration of the gap was systematically varied and the signal was placed both symmetrically and asymmetrically within the gap. The data were analyzed by assuming that the temporal window had the form of a simple mathematical expression with a small number of free parameters. The values of the parameters were adjusted to give the best fit to the data. The analysis assumed that, for each condition, the temporal window was centered at the time giving the highest signal-to-masker ratio, and that threshold corresponded to a fixed ratio of signal energy to masker energy at the output of the window. The data were fitted well by modeling each side of the window as the sum of two rounded-exponential functions. The window was highly asymmetric, having a shallower slope for times before the center than for times after. The equivalent rectangular duration (ERD) of the window was typically about 8 ms. The ERD increased slightly when the masker level was decreased, but did not differ significantly for signal frequencies of 500 and 2000 Hz. The temporal-window model successfully accounts for the data from a variety of experiments measuring temporal resolution. However, it fails to predict certain aspects of forward masking and of the detection of amplitude modulation at high rates.
Binaural unmasking in infants
Authors: Schneider Bruce A. , Bull Dale , Trehub Sandra E.
Published: October 2005

Localization responses to a broadband noise signal presented against a broadband noise masker were obtained from 12-month-old infants and adults. Two loudspeakers, one to the left and one to the right of the listener, continuously presented identical broadband maskers. On a trial, a broadband signal was added to one of the loudspeakers. Subjects were required to identify the loudspeaker producing the signal. Noise signals were either coherent (from the same noise generator) or incoherent (from an independent noise generator). Both infants and adults found it easier to locate the incoherent signals even when the two types of signals were adjusted to produce equal increments in power. Since monaural performance, after this adjustment, should be equivalent for the two cases, superior performance for incoherent signals implies that binaural processing is involved. The same result was observed in control experiments in which coherent and incoherent signals were presented over earphones to adults. These results suggest that the mechanisms responsible for binaural unmasking are operative by 12 months of age.
Auditory temporal acuity in relation to category boundaries; speech and nonspeech stimuli
Authors: Kewley-Port Diane , Watson Charles S. , Foyle David C.
Published: October 2005

Experiments were conducted to determine the underlying resolving power of the auditory system for temporal changes at the onset of speech and nonspeech stimuli. Stimulus sets included a bilabial VOT continuum and an analogous nonspeech continuum similar to the ‘‘noise-buzz’’ stimuli used by Miller et al. [J. Acoust. Soc. Am. 60, 410–417 (1976)]. The main difference between these and earlier experiments was that efforts were made to minimize both the trial-to-trial stimulus uncertainty and the cognitive load inherent in some of the testing procedures. Under conditions of minimal psychophysical uncertainty, not only does discrimination performance improve overall, but the local maximum, usually interpreted as evidence of categorical perception, is eliminated. Instead, discrimination performance for voice onset time (VOT) or noise lead time (NLT) is very accurate for short onset times and generally decreases with increasing onset time. This result suggests that ‘‘categorization’’ of familiar sounds is not the result of a psychoacoustic threshold (as Miller et al. have suggested) but rather of processing at a more central level of the auditory system.
Use of focused ultrasonic receivers for remote measurements in biological tissues
Authors: Gavrilov Leonid R. , Dmitriev Vladimir N. , Solontsova Lyudmila V.
Published: October 2005

The feasibility of using a focusing ultrasonic transducer as a sound pressure receiver is discussed. It is shown theoretically that, at certain angular apertures of the receiver, its output signal is proportional to the sound pressure in the field point coincident with the receiver center of curvature. The receivers of this type have been demonstrated suitable for remote measurements of field spatial distribution of plane and focused ultrasonic radiators. Data are presented on the experimental testing of focused receivers in measuring acoustic fields in water, air, and certain samples of biological tissues. The instruments are sufficiently universal and allow the measurement not only of acoustic fields, but also of temperature increments in locally heated media, as well as permit one to follow the initiation and development of ultrasonic cavitation and study nonlinear effects. The remote sensing ability and high sensitivity of focused ultrasonic receivers allow their practical use in biomedical acoustics for noninvasive measurements.
Imitation of a VOT continuum by native speakers of English and Spanish: Evidence for phonetic category formation
Authors: Flege James Emil , Eefting Wieke
Published: October 2005

This study examined imitation of a voice onset time (VOT) continuum ranging from /da/ to /ta/ by subjects differing in age and/or linguistic experience. The subjects did not reproduce the incremental increases in VOT linearly, but instead showed abrupt shifts in VOT between two or three VOT response ‘‘modes.’’ The location of the response shifts occurred at the same location as phoneme boundaries obtained in a previous identification experiment. This supports the view that the stimuli were categorized before being imitated. Children and adults who spoke just Spanish generally produced only lead and short-lag VOT responses. English monolinguals tended to produce stops with only short-lag and long-lag VOT values. The native Spanish adults and children who spoke English, on the other hand, produced stops with VOT values falling into all three modal VOT ranges. This was interpreted to mean that they had established a phonetic category {th} with which to implement the voiceless aspirated realizations of /t/ in English. Their inability to produce English /p,t,k/ with the same values as native speakers of English must therefore be attributed to the information specified in their new English phonetic categories (which might be incorrect as the result of exposure to Spanish-accented English), to partially formed phonetic realization rules, or both.
Anisotropy of the ultrasonic backscatter of myocardial tissue: II. Measurements i
n v
i
v
o
Authors: Madaras E. I. , Perez J. , Sobel B. E. , Mottley J. G. , Miller J. G.
Published: October 2005

The purpose of this investigation was to determine the angular dependence of the backscatter from canine myocardial tissue in vivo and to compare it with the variation of backscatter over the cardiac cycle that has been recognized and reported previously. The backscatter was measured from regions of left ventricular wall in canine hearts in which the fibers of the muscle lay parallel to the surface of the heart and were oriented predominantly in a circumferential fashion. Because of technical considerations, the angle of insonification was varied systematically through two cycles in which the angle relative to the muscle fiber axes ranged from 60°–120°. Backscatter was maximum at angles of interrogation perpendicular to the myocardial fibers and minimum at those most acute (60°) relative to the orientation of the fibers. The previously observed variation of integrated backscatter over the heart cycle was evident at each angle of interrogation. At end systole, the average maximum-to-minimum angular variation of integrated backscatter as 5.0±0.4 dB. At end diastole, the average maximum-to-minimum angular variation was 3.2±0.4 dB. Thus, even though angular dependence of the backscatter from tissues with directionally oriented structures is substantial, the anisotropy does not account for cardiac-cycle-dependent variation of backscatter. Accordingly, the angular dependence should be incorporated in approaches to quantitative tissue characterization with ultrasound.
Response of an edge-supported, circular, foil electret earphone with radially varying parameters
Authors: Busch-Vishniac Ilene J.
Published: October 2005

Analytical and experimental investigations have shown that there is an upper limit to the sound-pressure level that can be produced in the ear canal by an edge-supported, circular, foil electret earphone driven at a given voltage. It is possible to increase the maximum achievable earphone sensitivity by allowing the transducer electrical, material, or geometrical properties to vary radially. Theoretical arguments limit the increase in maximum sensitivity to 6 dB or less. Consideration of the effects of a radially varying charge density distribution and airgap thickness suggest that a 5-dB increase in sensitivity is actually obtainable. The introduction of radially varying parameters could also be used to increase the maximum achievable sensitivity in a foil electret microphone. The static deflection analysis presented in the article is valid for circular, edge-supported, foil electret microphones as well as earphones.
The effect of electrode stiffness on the piezoelectric and elastic constants of a piezoelectric bar
Authors: Moffett Mark B. , Ricketts Donald , Butler John L.
Published: October 2005

Electrodes that are stiff and thick compared with the underlying piezoelectric substrate material can substantially change the effective piezoelectric and elastic constants from those values that would be obtained in the absence of electrodes. A simple analytical model for the stress distribution inside a composite piezoelectric bar, consisting of two outer electrode layers and one inner piezoelectric layer, is used to calculate the effective g31, g32, g33, and gh piezoelectric constants, as well as the effective si j (i, j=1,2,3) elastic compliance coefficients. Numerical results for copper-clad, voided poly(vinylidene fluoride) (PVDF) sheets are presented.
Acoustic diffraction by an absorbing finite strip in a moving fluid
Authors: Asghar S.
Published: October 2005

The diffraction of a line source of sound by an absorbing finite strip in the presence of a fluid flow is investigated. The problem is solved by a method due to Jones [Q. J. Math. 3, 189–196 (1952)] based on the Wiener–Hopf technique [B. Noble, The Wiener–Hopf Technique (Pergamon, London, 1958)]. The diffracted field is shown to be the sum of a field produced by the two edges of the strip and a field due to the interaction of the two edges. The farfield is then calculated using asymptotic approximations.
Maintenance of intraoral pressure during speech after maxillary resection
Authors: Minsley Glenn E. , Warren Donald W. , Hinton Virginia
Published: October 2005

Although structural defects such as cleft palate and severe anterior open bite alter vocal tract resistance, compensatory responses usually result in maintaining consonant pressures at an adequate level. The purpose of the present study was to determine if individuals with an acquired palatal defect spontaneously develop similar compensatory behaviors. The pressure-flow technique was used to measure aerodynamic variables associated with consonant production after surgery and obturation. Although intraoral pressures decreased considerably immediately after surgery, pressures were maintained at a mean level of 3.5-cm H2O. Respiratory volumes increased as much as fourfold without obturation and were normal with obturation. Voice–voiceless differences in air volumes among consonants were maintained even in the presence of the defect. These findings suggest that compensatory responses are directed toward maintaining an appropriate level of intraoral pressure for consonant production.
Evidence of high-frequency acoustic emissions from the white-beaked dolphin (L
a
g
e
n
o
r
h
y
n
c
h
u
s a
l
b
i
r
o
s
t
r
i
s)
Authors: Mitson R. B. , Morris R. J.
Published: October 2005

Recordings of the signals from a school of white-beaked dolphins show that the frequency of their acoustic emissions extends to at least 305 kHz. These signals were detected by a sector scanning sonar used as a passive listening device of high bearing and time resolution. The records contain three types of signal, one of high intensity, one of a variable high repetition rate, and another showing a time-varying effect. Acoustic signals radiated by dolphins have been recorded and studied over a long period of time by many investigators. The purpose of this letter is to report evidence that acoustic emissions from white-beaked dolphins have significant energy at frequencies around 305 kHz, about one octave higher than previously observed. The observations discussed here were made aboard the fisheries research vessel Clione in the Wellbank flat area of the southern North Sea on 13 June 1970 between 1040 and 1110 h. When the dolphin signals were observed, the transmitter of the sector-scanning sonar in use was turned off, and the system was utilized as a passive listening device of high bearing and time resolution.
Guided waves in a moving layer of fluid
Authors: Cooper Jeffery , Guillot Jean Claude
Published: October 2005

It is shown that under certain conditions a moving layer of fluid can function as an anisotropic waveguide for acoustic waves. An asymptotic formula is obtained for the frequencies of the guided waves.
Equivalent-network representations of the generalized Hooke’s law for isotropic materials
Authors: Rudgers Anthony J.
Published: October 2005

It is shown that the generalized Hooke’s law—the constitutive relation for all solid materials that behave mechanically in a linear fashion—defines the topology of equivalent networks analogous to such solids insofar as mechanical behavior is concerned. Two equivalent networks are reported, one representing each of the two forms in which Hooke’s law is usually expressed. Each analog is a six-port network that can be decomposed into a pair of independent three-port networks. One three-port network in each pair reflects the extensional behavior of a material and one its distortional behavior. Elastic moduli and compliances appear as immittances in the networks. Since network topology is determined only by the analytic form of Hooke’s law and by the symmetry intrinsic in the material considered, such immittances can be mathematical entities more general than complex quantities. Some results from linear elasticity theory are interpreted using the analog networks, and their application in describing the viscoelastic behavior of materials is considered briefly. The analysis pertains principally to homogeneous isotropic materials.
Interaction of sound waves. Part III: Two real beams
Authors: Tjo/tta Jacqueline Naze , Tjo/tta Sigve
Published: October 2005

This article is a theoretical study of the nonlinear interaction between two sound beams in a lossless fluid, intersecting each other at arbitrary angles. The governing equation for the sum and difference frequency components is solved in the quasilinear approximation for prescribed conditions on the sources of the two beams. A solution that is uniformly valid in space is obtained in the form of a Fourier integral. Asymptotic evaluations at large distance from the sources lead to simple formulas that relate the amplitude and phase of the generated sound to the on-source conditions. Diffraction effects are fully accounted for, and shown to be important even at large distances. Relevance to earlier literature on the scattering of sound by sound is discussed.
Nonlinear bubble dynamics
Authors: Prosperetti Andrea , Crum Lawrence A. , Commander Kerry W.
Published: October 2005

The standard approach to the analysis of the pulsations of a driven gas bubble is to assume that the pressure within the bubble follows a polytropic relation of the form p=p0(R0/R)3κ, where p is the pressure within the bubble, R is the radius, κ is the polytropic exponent, and the subscript zero indicates equilibrium values. For nonlinear oscillations of the gas bubble, however, this approximation has several limitations and needs to be reconsidered. A new formulation of the dynamics of bubble oscillations is presented in which the internal pressure is obtained numerically and the polytropic approximation is no longer required. Several comparisons are given of the two formulations, which describe in some detail the limitations of the polytropic approximation.