bluuebunny/crossref_metadata_2025 huggingface dataset:
Reflection and transmission of acoustic wideband plane waves by layered viscoelastic media
Authors: Stepanishen Peter R. , Strozeski Bernard
Published: October 2005

The reflection and transmission of acoustic wideband plane waves by layered viscoelastic media is addressed via the use of transfer matrix and Fourier transform methods. Both the reflected and transmitted time dependent pressures are expressed as convolution integrals which involve the incident pressure and a reflected or transmitted impulse response, respectively. The impulse responses are equivalent to the inverse Fourier transforms of the pressure reflection and transmission coefficients which are obtained by transfer matrix methods for layered viscoelastic media. Numerical results for reflected and transmitted pressures are presented to illustrate the nature of the precursors and the distortion of the incident pulse as a function of incident angle and layer configuration. These results, which were obtained via the use of FFT methods, illustrate the effect on the reflected and transmitted pressures of losses within the layers.
Radially propagating surface and plate waves
Authors: Pardee W. J.
Published: October 2005

Families of radially propagating exact solutions of the elastic wave equation with stress-free boundaries on a surface and on a plate are described. The waves are characterized by angular dependence exp(imϑ) with m an arbitrary integer. The relationship to plane-wave Rayleigh waves and plate modes is demonstrated and possible applications to ultrasonic inspection mentioned.
Discussion of detection threshold with reverberation limited conditions
Authors: Kroenert J. T.
Published: October 2005

A formulation for the detection threshold of a sonar receiver operating with a reverberation background is derived. The similarity of the result to the noise-limited detection threshold is briefly discussed.
Preliminary data on frequency discrimination in infancy
Authors: Olsho Lynne Werner , Schoon Celia , Sakai Ron , Turpin Robin , Sperduto Vincent
Published: October 2005

An operant head-turn technique was used to measure frequency-difference thresholds for 5- to 8-month old infants and for adults. At a standard of 1000 Hz, presented at 70 dB above adult threshold, infant thresholds averaged 21.6 Hz, adult thresholds, 7.4 Hz. In a two-alternative forced choice procedure, difference thresholds of the same adults approached those reported by Wier et al. [J. Acoust. Soc. Am. 61, 178–184 (1977)].
Combination bands and the measurement of the auditory filter
Authors: Lutfi Robert A. , Patterson Roy D.
Published: October 2005

An experiment was conducted to determine if combination bands generated by the interaction of signal and noise distorts measures of the auditory filter shape. Probe tones with frequencies of 0.68, 0.76, 0.84, 0.92, and 1.0 kHz were used to measure the masking patterns produced by (1) a notched noise with edges at 0.6 and 1.2 kHz, (2) a high-pass noise with cutoff at 1.2 kHz, and (3) a high-pass noise (cutoff 1.2 kHz) combined with a 1.0-kHz tone. The results show that the cubic difference band, generated by the interaction of the 1.0-kHz tone and the nearest components of the high-pass noise, produces little if any masking over and above that produced by the high-pass noise alone, and far less masking than the notched noise produces in the same region. Within the framework of a power-spectrum model of masking, the data indicate that this type of combination band does not distort the shape of the auditory filters derived previously with notched noise maskers.
Resonance theory of the effective properties of perforated solids
Authors: Gaunaurd G. C. , Überall H.
Published: October 2005

We develop an analytic, unified, and systematic methodology based on scattering theory, for determining the dynamic (frequency-dependent) effective properties of micro-inhomogeneous (visco) elastic media, such as effective elastic moduli, wave speeds, and wave attenuations. The small inhomogeneities are modeled deterministically as fluid-filled spherical cavities, and the Ament–Toksöz method for obtaining static effective properties is extended to the dynamic (resonant) case by retaining those higher-order terms in a long wavelength expansion which give rise to the ultrasonic resonances of the microinhomogeneities. Rescattering from the inhomogeneities has been neglected, thus restricting the applicability of our results to the case of moderate inhomogeneity concentrations. The results of the present analysis are affected by the presence of shear waves in the solid matrix, and they contain all the findings of our previous dynamic resonance theory of gas bubbles in liquids, as well as nearly all the static results available in the earlier literature which do not take rescattering effects into account, as particular cases. We graphically display many numerical results for fluid-filled cavities in rubber matrices.
Sampling rate reduction in multichannel processing of bandpass signals
Authors: Brown J. L.
Published: October 2005

The uniform sampling rate required to reconstruct a deterministic bandpass signal x(t) having spectrum confined to I1∪I2, where I1 = [−ω0−σ/2, −ω0+σ/2), I2 = [ω0−σ/2, ω0+σ/2) with ω0?σ/2≳0 depends critically on the positioning of the band and varies from σ/π to 2σ/π samples per second, the minimum rate of σ/π being attained if and only if ω0+σ/2 is an integer multiple of σ. If the bandpass signal x is now used as a common input to an even number m of linear time-invariant filters to produce m outputs z1(t),...,zm(t), then it is proved that, under a certain ’’independence’’ requirement on the filters (a matrix function condition), the input x may be reconstructed from samples of the outputs {zk(t)}, each output being sampled at the uniform rate of σ/mπ samples/second, or (1/m)th the minimum sampling rate associated with the input. The dependence on band position is removed by a partitioning of the set I1∪I2 into m disjoint subsets J1,...,Jm of equal length and a subsequent mapping procedure which allows J1 to be mapped (discontinuously) in a one-to-one manner onto Jk for 1?k?m. As an example, it is shown that samples of the bandpass signal x and its first derivative x′, taken at the common rate of σ/2π samples per second (m = 2), suffice to determine x completely, a generalization of an early theorem due to Fogel [IRE Trans. Inf. Theory, IT-1, 47–48 (1955)].
Forward and backward projection of acoustic fields using FFT methods
Authors: Stepanishen Peter R. , Benjamin Kim C.
Published: October 2005

The forward and backward propagation of harmonic acoustic fields using Fourier transform methods is presented. In particular, the forward propagation of a velocity distribution to obtain a pressure field and the backward propagation of a pressure field to obtain a velocity distribution are addressed. Numerical examples are presented to illustrate the nearfield behavior of the pressure field from complex planar vibrators, e.g,—an ultrasonic transducer or plate, with nonuniform velocity distributions. The numerical results, which were obtained via the use of FFT algorithms, are presented for vibrators which are operating above and below coincidence. These results illustrate the acoustic nearfield as a function of distance from the vibrator. Numerical results are also presented to illustrate the backward projection method. The pressure field of a 3×3 focused array is back projected to obtain the velocity distribution for several cases of interest. These results illustrate the utility of the transform method and the effect of spatial windows or filters in its implementation using FFT algorithms.
Ultrasonic absorption in aqueous organic mixtures. N, N-dimethylformamide and water at 25°C
Authors: Silber Herbert B. , Cervantes Richard A.
Published: October 2005

Ultrasonic absorption measurements on mixtures of water and N, N-dimethylformamide (DMF) demonstrate the existence of a frequency independent absorption at each composition. An analysis of the absorption as a function of water content reveals the presence of two maxima.
Correction procedure for measurements of the electroelastic effect in transverse fields
Authors: Reider Georg A. , Kittinger Erwin , Tichý Jan
Published: October 2005

The determination of the dependence of the elastic stiffnesses of an applied dc field (electroelastic effect) by means of ultrasonic velocity measurements presents difficulties when electric fields perpendicular to the propagation direction are applied. In such a geometry the field is disturbed by the transducer. The magnitude of the field therefore varies along the path of the ultrasonic pulses. A simple method, based on the variation of the size of the field generating electrodes, to correct the measured field effect is described.
Nearfield inverse scattering formalism for the three-dimensional wave equation: The inclusion of a p
r
i
o
r
i velocity information
Authors: Weglein A. B.
Published: October 2005

We address the problem of identifying a local velocity, c(r), in a three-dimensional scalar wave equation from nearfield data. The implicit model assumptions of previous nearfield inverse scattering procedures are examined. These assumptions cannot be reasonably assumed in certain applications. Therefore, a method for extending the range of validity of nearfield inverse scattering procedures is presented. In addition, we present a technique for incorporating a priori information or estimates into this formal wave equation inversion procedure. An approximate perturbative solution for this formalism has the ability to accommodate selective and potentially troublesome multiples within the Born model.
The phases of basilar-membrane vibrations
Authors: Geisler C. Daniel , Rhode William S.
Published: October 2005

Experimental phase data from the Mössbauer-effect measurements of basilar-membrane vibration are given. The phase lag increased with intensity for frequencies less than best frequency, but was a decreasing function of intensity above best frequency. A series of linear minimum-phase representations of the basilar membrane’s motion were also calculated; they show similar trends.
Acoustic invariance and the perception of place of articulation: A selective adaptation study
Authors: Landahl Karen L. , Blumstein Sheila E.
Published: October 2005

Two adaptation experiments were conducted exploring the perception of place of articulation in stop consonants. We hoped to determine whether in making a phonetic decision about place of articulation, the perceptual system is sensitive to subtle changes in the fine structure of a CV stimulus (i.e., onset formant frequencies and transition motions) when both the adapting and test stimuli shared the same invariant properties. These invariants are defined in terms of the gross spectral shape at stimulus onset. In the first experiment, the effects of adaptors varying in duration (full CV syllables or shortened CV syllables called onsets), vowel context ([a] versus [i]), onset formant frequencies, and presence or absence of moving transitions were tested on CV [ba da ga] test stimuli. All adaptors contained sufficient information to extract the invariant properties for place of articulation based on spectral shape at consonant release. Results showed that the various onsets did not adapt full CV [ba da ga] test stimuli. In the second experiment, the effects of the onset adaptors were tested on onset CV [ba da ga] test stimuli. Results showed that onsets can adapt an onset place of articulation continuum in a manner similar to place of articulation adaptation using full CV syllables. Further, the fine structure of the stimuli significantly affected the adaptation results. Finally, vowel contingency effects seem to reflect differences in onset frequencies of the consonants in CV syllables rather than the steady-state frequencies of the following vowels.
Melodic accent: Experiments and a tentative model
Authors: Thomassen Joseph M.
Published: October 2005

The perception of accent in tone sequences is a constructive process in which physical cues are matched against anticipated accents. The anticipation of the observer can experimentally be controlled by embedding the short tone sequence to be investigated in a context with a meter: method of controlled anticipation. An investigation of melodic accentuation, resulting from the succession of frequency intervals, revealed that in principle every change of frequency level between two successive tones can be interpreted as accentuation of the terminal tone of the change. The melodic contour seems to be most important. The first of two intervals in opposite directions operates as the strongest accentuation, whereas two intervals in the same direction are equally effective. The effect of relative magnitude is less pronounced. Only in the case of clearly diverging relative magnitudes the largest interval is the most powerful, particularly when the intervals are in the same direction. The advantage of rises over falls is almost negligible. The short-term influence of physical factors on momentary accent perception allows for a description in terms of a ’’memory window’’ sliding along the tone sequence. At each moment the frequencies within the window provide the physical cue for accent that has to be matched against anticipation. If the span of the window is minimal, i.e., three tones, accent perception in sequences of four tones, embedded according to the method of controlled anticipation, has been accounted for fairly well, the correlation coefficient between predictions and outcomes being 0.76.
Acoustic wave scattering from a fluid/solid periodic rough surface
Authors: Chuang Shun-Lien , Johnson Richard K.
Published: October 2005

A rigorous theory based on the extended boundary condition method is proposed to solve the problem of elastic wave scattering from a periodic fluid/solid interface. The diffraction efficiencies of the reflected compressional wave in the fluid and the transmitted shear and compressional waves are calculated. The energy conservation criterion is used to check the accuracy of the numerical results. The effect of loss (viscoelasticity) in the solid is also included. The wave diffraction from a water and acrylic rough surface is measured. Good agreement between the theory and the experiment is obtained.
Effects of low-frequency biasing on auditory-nerve activity
Authors: Schmiedt Richard A.
Published: October 2005

Intensity functions of single fibers in the auditory nerve of gerbils were obtained to tone bursts alone and tone bursts superimposed on a low-frequency biasing signal. The bias was a triangular sound-pressure waveform with a period of 100 ms and was usually presented at 90 dB SPL. Cochlear microphonics (CM) recorded in scala media of the basal and second turns of the cochlea were trapezoidal in shape in response to the triangular waveform of sound pressure. Assuming the CM waveform reflects basilar-membrane displacement at very low frequencies, it is concluded that the input impedance of the gerbil cochlea is substantially resistive at frequencies as low as 10 Hz. Intensity functions of single fibers with characteristic frequencies (CFs) below about 12 kHz exhibited enhanced thresholds to CF tones associated with basilar-membrane displacement toward scala tympani; conversely, thresholds to CF tones were suppressed during displacement toward scala vestibuli. Tone-alone thresholds were usually between the two biased conditions. The bias had little effect on responses of tones placed below or above CF and on the activity of fibers with CFs greater than about 12 kHz. These physiological results are compatible with corresponding psychophysical measures obtained from human observers.
An adaptive nulling technique for signal reception
Authors: Reddi S. S.
Published: October 2005

An adaptive technique capable of eliminating directional noise sources is presented for linearly spaced sensor elements. The technique utilizes the signal nulling properties of the eigenvectors corresponding to the minimal eigenvalue of the covariance matrix of the received signal vector. To receive signals in a specified direction, a null elimination method using polynomial divide is described. The proposed technique is applicable for sensors with independent white self-noises of identical variance, and external point signal/noise sources.
Effects of the sub-surface bubble layer on sound propagation
Authors: Novarini Jorge C. , Bruno Daniel R.
Published: October 2005

Based on photographic data of bubble populations and theoretical considerations, a formula for the spectrum of wind-generated bubbles in the open sea is derived. This formula is used in a computer study to calculate the full effect of bubbles on refraction and attenuation in sound propagation both in the surface duct and in vertical paths. The study is carried out for frequencies in the range 8–60 kHz, and wind speeds to 30 kn. Attenuation is found to be very significant in this range. For practical purposes formulae for the loss per limiting ray cycle and for the two-way attenuation in a vertical path are obtained by fitting the numerical results. These formulae can be easily implemented on hand-held calculators.
On scatter from a rough interface
Authors: Tolstoy I.
Published: October 2005

Earlier work on coherent scatter from a rough boundary between fluids of different densities demonstrated the existence of a boundary wave due to multiple coherent scatter. This note points out needed modifications to some of the numerical constants.
Cochlear drainage and basilar membrane tuning
Authors: Patuzzi R. , Sellick P. M. , Johnstone B. M.
Published: October 2005

We have demonstrated that drainage of the scala tympani, even though it produces a large loss of sensitivity, does not produce a change in best frequency.
Experiments on the single woodwind tone hole
Authors: Keefe Douglas H.
Published: October 2005

Impedance parameters associated with the lumped T circuit representing the tone hole in the woodwind musical instrument transmission-line model are measured for two types of tone holes. One type has a diameter large relative to the height of the tone-hole chimney, as on the saxophone. The other type has a chimney height nearly equal to the hole diameter, as on the clarinet. The imaginary parts of the series and shunt impedances, measured under small signal conditions, agree with predicted values, and the closed-hole series impedance data agree with earlier data of Nederveen and van Wulfften Palthe [Acustica 13, 65–70 (1963)]. A semi-empirical expression is deduced, by use of measurements of Bouasse [Tuyaux et Resonators (Librairie Delagiare, Paris, 1929), p. 239], Benade and Murday [J. Acoust. Soc. Am. 41, 1609 (1967)], and the theory of Keefe [J. Acoust. Soc. Am. 72, 676 (1982)], for the open-hole effective length te of a tone hole with a pad suspended above it. This expression correctly predicts the values of te for the two types of tone holes measured as well as for the flute tone-hole data obtained by Coltman [J. Acoust. Soc. Am. 65, 499–506 (1979)]. The open-hole shunt resistance, which includes radiation loss from the open-hole, viscous shearing loss in the bulk of the air, and wall loss at the sharp corners of the hole and within the hole chimney, is measured. The ratio of the radiation resistance to the total shunt resistance for a single hold varies systematically with frequency. This ratio is low at low frequencies due to large losses at the corners and edges, is a maximum near 750 Hz for sax-type holes and decreases again at higher frequencies due to increased shearing losses.
On the failure of the Kirchhoff assumption in backscatter
Authors: Jebsen Gary M. , Medwin Herman
Published: October 2005

Diffraction backscatter from a semi-infinite plate and from a rigid plane wedge is studied in the time and frequency domains. The spectrum of diffraction backscattered sound for a point source, as predicted by use of the Kirchhoff assumption in the Helmholtz–Kirchhoff integral formulation, is compared to experimental results and is found to be substantially incorrect. The errors are very large when the least time path to the diffracting edge is near grazing, for example, 30 dB error at θ=4° to the plate. The Fourier transform of the Biot–Tolstoy closed form, normal coordinate, impulse solution gives accurate predictions of the experimental measurements in the frequency domain.
Sound absorption based on ocean measurements. Part II: Boric acid contribution and equation for total absorption
Authors: Francois R. E. , Garrison G. R.
Published: October 2005

The absorption of sound in seawater is considered as the sum of three contributions: those from pure water, magnesium sulfate, and boric acid. Contributions from other reactions are small and are not included. The pure water and magnesium sulfate contributions obtained from analyses of extensive oceanic measurements, including many in the Arctic, were discussed in Part I. In Part II, an analysis is made of all reported measurements in the low-frequency region (0.2–10 kHz) to evaluate the contribution of boric acid. This is done by subtracting the pure water and magnesium sulfate contributions determined in Part I from the total absorption to give a more accurate estimate of the boric acid contribution than previously obtained. The three contributions are then combined to form an equation with both a theoretical basis and a satisfactory empirical fit that will be useful to researchers and engineers in the field of underwater sound. The equation applies to all oceanic conditions and frequencies from 200 Hz to 1 MHz.
Ultrasonic inspection of fiber suspensions
Authors: Dion J. L. , Malutta A. , Cielo P.
Published: October 2005

An acousto-optical method for the inspection of fibrous materials is presented, with particular regard to paper mill applications. This technique permits very fast on-line differentiation between pulp suspensions containing fibers of different average sizes. The basic principle is presented which is related to the Rayleigh disk phenomenon, as well as preliminary experimental results.
Coupling of Lamb waves with the aperture between two elastic sheets
Authors: Rokhlin S. I. , Bendec F.
Published: October 2005

The interaction between ultrasonic Lamb waves and the region of rigid contact between two elastic layers is explored analytically. This problem is a model of two sheets welded in this region, and is of great practical importance in a nondestructive evaluation of welds. To uniquely define the dimensions of the region on the basis of the transmitted ultrasonic signal, the experimental conditions are selected in such a manner as to avoid resonance in the region of contact. Our experiments show that there exists a one-to-one relationship in the form of T∼d3 between the transmission coefficients T of the wave through a region of contact having diameter d.
The effect of test difficulty on the sensitivity of speech discrimination tests
Authors: Dillon Harvey
Published: October 2005

The sensitivity of speech discrimination tests is defined as being large if a small change in experimental conditions causes a large and repeatable change in test score. The aim of this paper is to investigate ways by which test sensitivity can be maximized. The effect of test difficulty on sensitivity is examined by the use of a model based on signal detection theory and subjective similarity rating concepts. For several sets of assumptions about the parameters underlying the perceptual processes, the model indicates that test difficulty should be in the range 73% to 87% to achieve the maximum sensitivity with speech tests using between four and eight response foils. The model results also indicate that the sensitivity increases with the number of response foils. When the variation of test reliability with test difficulty is taken into account, the test difficulty which maximizes the sensitivity/reliability trade-off lies in the range 85% to 90%. It is argued that irrespective of the optimum test difficulty, a maximally sensitive test will contain items equal to one another in difficulty.
High temperature acoustic bond compatible with fluoride fluorites
Authors: Foster R. B. , Brewer J. A. , Montgomery S. R. , Pederson D. O.
Published: October 2005

In order to study metal fluorides of the fluorite structure at temperatures greater than 650 °K using ultrasonic techniques, several previously reported acoustic bonds were found to be inadequate. DuPont 9770 silver–platinum paste has been found to act as an effective acoustic bond for longitudinal ultrasound in contrast to the usual high temperature oxide acoustic bonds which break because they interact strongly with fluoride materials. Measurements of longitudinal ultrasonic velocities have been made up to 796 °K in [110] oriented CdF2 and up to 850 °K in [100] oriented BaF2. In neither of these measurements did the bonds break at the highest temperatures.
Visual and tactual perception of syllable number in sentence stimuli
Authors: Bourgeois Michelle S. , Goldstein Howard
Published: October 2005

The purpose of this study was to determine whether suprasegmental information could be perceived by artificially deafened subjects via the Multipoint Electrotactile Speech Aid (MESA) so as to enhance the visual perception of connected discourse. This study compared subjects’ untrained ability to perceive the number of syllables in sentence stimuli in three conditions: Visual Alone (VA), Tactile Alone (TA), and Tactile plus Visual (TV). Five adults tapped the temporal pattern of stimuli using a telegraph key. Stimuli consisted of 1-, 3-, 5-, and 7-syllable meaningful sentences and 5- and 7-syllable (nonmeaningful) second-order sentences. The subjects perceived correctly a mean of 37% of the stimuli in the TA condition, and approximately 60% of the stimuli in the VA and TV conditions. Three possible explanations are offered to account for these results: (1) the limitations of the MESA’s electrocutaneous transform of the speech signal, (2) the sensory limitations of the skin, and (3) the absence of extensive training.
Probability density estimates of surface and bottom reverberation
Authors: Wilson Gary R. , Powell Dennis R.
Published: October 2005

Selected surface reverberation and bottom reverberation returns were used to compute estimates of the probability density function of the instantaneous reverberation. To estimate the densities, 6500 samples of surface reverberation and 3078 samples of bottom reverberation were used. The collections of samples were tested for randomness, independence, homogeneity, and normality. Both the surface and bottom reverberation were found to be non-Gaussian. Kernel density estimation techniques were applied to the collections of samples to provide univariate estimates of the densities. The densities were seen to be nearly Gaussian, but with heavier tails. Heavier tailed densities generally result in higher false alarm rates for detectors designed for a Gaussian noise process.
A method for constructing wave velocity and density profiles from the angular dependence of the reflection coefficient
Authors: Hooshyar M. A. , Razavy M.
Published: October 2005

If the acoustic wave velocity and the density of an inhomogeneous medium are dependent on one of the coordinates only, then it is possible to express the logarithmic derivative of the pressure along this coordinate as a nonlinear first-order differential equation. In the present work a particular finite difference approximation to this equation is found which allows one to obtain the reflection coefficient as a ratio of two polynomials involving the sine of the angle of incidence. In this way one can find, in a very simple way, the unknown coefficients of the two polynomials from the values of the reflection coefficient for different angles, and at the same time one can determine the wave velocity and the density, from the unique continued fraction expansion of this rational representation for two different frequencies.
A procedure for detecting variability of psychophysical thresholds
Authors: Hall J. L.
Published: October 2005

In adaptive psychophysical testing, it is desirable to identify experimental runs during which the subject’s threshold changes. This is not easy to do, because the testing level changes during the course of the run. The following screening procedure can assist in detecting threshold variability. At the conclusion of the run, determine for each trial the discrepancy between observed and expected response. Next, determine the linear regression of this discrepancy upon trial number. If the subject’s response behavior is stable and well described by the psychometric function, then the expected value of slope of the linear regression is equal to zero. If the observed slope differs greatly from zero, then it is unlikely that the subject’s response behavior is stable. Results from computer simulations and psychophysical experiments are presented.
Feynman diagram analysis of transducer impulse response
Authors: Banah A. H. , Korpel A. , Vogel R. F.
Published: October 2005

Transducer impulse response is analyzed by introducing two novel elements. First, the usual equivalent circuit of the transducer is replaced by a simple reentrant transmission line configuration. Second, a Feynman diagram method is applied which involves tracing the exciting signal through all possible pathways to the time and place of observation. The theory is applied under various conditions of electrical and acoustical loading, and results compared with computer simulations and physical experiments.
Piezo-acoustic rotation in crystals
Authors: Kumaraswamy K. , Krishnamurthy N.
Published: October 2005

A relationship between acoustic and optical gyrotropic tensors is given. The effect of stress on acoustical activity for crystals belonging to D3, S4, and Td point groups is studied and it is found that in the acoustically inactive S4 and Td point groups, for unaxial stress along x direction and for propagation along z direction, the degeneracy of the shear wave is lifted giving rise to left-elliptical and right-elliptical polarized modes. The experimental method of observing such splittings is suggested.
Weak and short waves in inhomogeneous isotropic elastic materials. I.
Authors: Tokuoka Tatsuo , Shimauchi Katsuyuki
Published: October 2005

Wave propagation in an elastic material is investigated theoretically. The material is assumed to be isotropic and inhomogeneous and to have a nonlinear stress–strain relation, and the prestrain is assumed to be dynamic and inhomogeneous. Geometrical acoustics is applied, and the wave is assumed to be weak and short and to have an arbitrarily curved wave front. The amplitude is less than the wavelength, and the wavelength is less than the distances over which such wave quantities as prestrain and stress are subject to considerable change. By equating first-order terms, a principal longitudinal and two principal transverse waves are shown to exist and their speeds of propagation are evaluated. Likewise, by equating second-order terms, amplitude equations which govern the growth and decay of amplitude are derived. The variation of amplitude depends upon the curvature of the wave front, the velocity gradient and prestrain and material inhomogeneities, the nonlinearity of the stress–strain relation, and the waveform. The results obtained in simple cases are identical with those derived using the method of singular surface.
Effective masking bandwidths at low frequencies
Authors: Fidell Sanford , Horonjeff Richard , Teffeteller Sherri , Green David M.
Published: October 2005

Masking of low-frequency sinusoids of varying durations by Gaussian noise of varying spectral shape was measured in three different studies. Common solutions to technical problems associated with control and specification of low-frequency signals were used in the three studies. If interpreted in terms of Fletcher’s critical ratio assumptions, data from the first study lead to the inference that the masking bandwidth is inversely related to signal frequency below about 200 Hz. Data from the second study rule out the likelihood that the apparent increase in masking bandwidth is attributable to changes in auditory integration times at low frequencies. The data of the third study suggest that the apparent increase in auditory filter bandwidth at low frequencies is more adequately explained by a decrease in observers’ detection efficiency than by broadening of the filter bandpass.
Psychophysical measures of two-tone suppression and distortion products (2f1−f2) and (f2−f1)
Authors: Humes Larry E.
Published: October 2005

Psychophysical two-tone suppression and the growth of the (2f1−f2) and (f2−f1) distortion products were measured in four normal-hearing young adults using a forward-masking paradigm. The stimulus parameters investigated were: (1) f1=750 and 3000 Hz; (2) f2/f1=1.11, 1.26, and 1.41; (3) L1=50, 65, 80, and 90 dB SPL; and (4) L2−L1 varied from −20 to +20 dB in 10-dB increments. It appears that the p-law class of nonlinearity, which maintains that suppression and growth functions for the distortion products are directly related, is not supported by the data. Of existing models of aural nonlinearity, Goldstein’s [J. Acoust. Soc. Am. 41, 458–479 (1967)] normalized power series appears to provide the most accurate description of the data, especially when modifications brought about by suppression are incorporated into the model.
Place cues for nasal consonants with special reference to Catalan
Authors: Recasens Daniel
Published: October 2005

This study investigates the perceptual contributions of formant transitions and nasal murmurs to the identification of the unreleased Catalan nasal consonants [n], [ν], [∥] (alveolar, palatal, velar, respectively) after [a] in absolute final position. Transition and murmur patterns were synthesized and varied simultaneously and systematically by interpolating between optimal values obtained from spectrographic analysis of natural speech. Catalan subjects were asked to identify the synthetic stimuli as [n], [ν], and [∥]. The main findings were: (1) Although transitions provided more effective cues for place of articulation than murmurs, the murmurs did make a significant contribution to the [∥]–[n] distinction. (2) The cue value of the transitions ([ν]>[n], [∥]) was inversely related to that of the murmurs ([∥], [n]>[ν]). It is concluded that static and dynamic place cues for nasals in an [aC♯] context are perceptually integrated with reference to the typical pattern of production of these consonants.
Surface acoustic admittance of highly porous open-cell, elastic foams
Authors: Lambert Robert F.
Published: October 2005

This work presents a comprehensive study of the surface acoustic admittance properties of graded sizes of open-cell foams that are highly porous and elastic. The intrinsic admittance as well as properties of samples of finite depth were predicted and then measured for sound at normal incidence over a frequency range extending from about 35–3500 Hz. The agreement between theory and experiment for a range of mean pore size and volume porosity is excellent. The implications of fibrous structure on the admittance of open-cell foams is quite evident from the results.
Target strength of liquid-filled spheres
Authors: Folds Don L. , Loggins Chester D.
Published: October 2005

The liquid-filled target sphere is a high target strength reflector which, since its first use in 1971, has proven to be of great utility in sonar research. The spherical metal shell filled with a low-velocity liquid is being used as a calibrated, passive, aspect-independent target. To date, the characteristics of this target have only been described in a narrow ka range by simple ray theory models. In this paper, a comprehensive treatment for 0<ka<100 for various shell materials and filling fluid refractive indices is presented, using results from wave theory analyses. Comparisons are made with air-filled and water-filled spheres and with solid spheres. Form function versus ka plots, echo time history, and target strength versus frequency are presented. Results show good agreement between computed and measured target strengths and permit an accurate prediction of target strength over a wide range of frequency and fluid velocities.
Waterborne noise due to ocean thermal energy conversion plants
Authors: Janota Claus P. , Thompson Donald E.
Published: October 2005

Public law reflects a United States national commitment to the rapid development of Ocean Thermal Energy Conversion (OTEC) as an alternate energy source. OTEC plants extract the stored solar energy from the world’s tropical seas and in so doing pose a potential for altering the character of the ambient noise there. The sources of noise from an OTEC plant are analyzed in the context of four configurations, two of which were built and tested, and two which are concepts for future full-scale moored facilities. The analysis indicates that the noise resulting from the interaction of turbulence with the seawater pumps is expected to dominate in the frequency range 10 Hz to 1 kHz. Measured radiated noise data from the OTEC-I research plant, located near the island of Hawaii, are compared with the analysis. The measured data diverge from the predicted levels at frequencies above about 60 Hz because of dominant non-OTEC noise sources on this platform. However, at low frequency, the measured broadband noise is comparable to that predicted.
Acoustic-reflex activity and behavioral thresholds following exposure to noise
Authors: Gerhardt Kenneth J. , Hepler Ernest L.
Published: October 2005

The relationships between properties of the acoustic reflex and temporary threshold shift (TTS) were examined in eight subjects exposed to a 95 dB SPL, 1.0-kHz octave-band noise for 4 h. The specific pattern of TTS obtained from this exposure was consistent with the expected sensitivity changes along the cochlear partition. Maximum decrease in behavioral thresholds was noted at 1.4 kHz with significant TTS also occurring at 2.0 and 4.0 kHz. Behavioral threshold at 0.5 kHz, one octave below the center frequency of exposure, was not affected. Significant reflex threshold shift (RTS) occurred at 1.4 and 2.0 kHz. In addition, RTS was noted at 0.5 kHz in the absence of any change in behavioral sensitivity at that frequency. Magnitude of the acoustic reflex was examined from threshold to 10-dB sensation level. A systematic reduction in magnitude was noted during the noise exposure for 1.4 and 2.0 kHz. The same pattern did not emerge for 0.5 kHz. Magnitude of the acoustic reflex pre-exposure was significantly correlated to TTS at 1.4 kHz. Changes in acoustic reflex thresholds and magnitudes followed the same time course as changes in behavioral thresholds during the growth and recovery periods.
On the plane-wave reflection coefficient and nonspecular reflection of bounded beams for layered half-spaces underwater
Authors: Bogy D. B. , Gracewski S. M.
Published: October 2005

We study the recently derived reflection coefficient for plane waves in a liquid that are incident on the liquid–solid interface of a solid half-space, which consists of a single layer of one elastic material bonded to a substrate of a different material. Plots of the magnitude of the reflection coefficient versus the incident angle are presented for many sets of material parameters and values of frequency f and layer thickness d. The use of the results presented for the study of nonspecular reflection of bounded acoustic beams is of primary interest. We therefore seek to identify all the critical incidence angles for nonspecular reflection. We find that nonspecular reflection can occur, not only in connection with surface waves that are purely propagating modes in the absence of the liquid, but also for leaky modes on a layered half-space, provided the leakage is not too great. We also investigate, in particular, the surface wave propagation for the case of a stiff layer on a soft half-space, and we find that the purely propagating mode cuts off with increasing fd when its speed reaches the shear wave speed of the substrate, as reported in the literature. However, as fd increases further, a leaky mode appears that approaches the Rayleigh wave for the layer. This leaky mode is also associated with nonspecular reflection for large enough fd.
Inverse scattering in a stratified medium
Authors: Stickler D. C.
Published: October 2005

In this analysis the following problem is considered: A point harmonic source at frequencies ω1 and ω2 is located in the region z<0, where the assumption is made that both the sound speed and density profiles are known. For z>0 the sound speed and density profiles are unknown. These two profiles are recovered from a measurement of the pressure field for all r at some fixed depth z<0 at the two frequencies. Trace formula methods are used. The following assumptions are needed: First, c(z) and ρ(z) approach c1, ρ1 as z→−∞, and c2, ρ2 as z→+∞, and although c2, ρ2 are not known, it must be known that c2>c1. Second, the angular frequency of the source must be such that no trapped modes are excited. While the sound speed c(z) can be complex, the limiting values c1 and c2 must be real. If c(z) also depends on frequency and the form of the dependence is known, say, c(z)=cR(z) +iωλ(z)cI(z), then cR(z), cI(z), and λ(z) can be recovered. Explicit expressions are obtained in the realistic case when cI(z) is not large. If a density is known and cI(z) =0, then only a measurement at one frequency is required. Two numerical examples are given; in both examples ρ(z)≡1 and c(z) is real. The first example is for a monotically increasing profile and the second has a low velocity zone. Typical sediment parameters are used.
A Lamb wave voltage sensor
Authors: Toda Kohji , Mizutani Koichi
Published: October 2005

A voltage sensor using a Lamb wave delay line oscillator is described. The device consists of two pairs of interdigital transducers and one plate electrode at the central part of the device. All of these transducers have the counter electrodes on the bottom surface of the substrate. The oscillation frequency of the device changes significantly with the voltage applied to the central plate electrode. Performances of the voltage sensor are given, including sensitivity and its frequency dependence.
Effect of half-wavelength membranes on the axial resolution of real-time ultrasonic scanners
Authors: Ophir Jonathan , Narayana P. A.
Published: October 2005

The effect of interposing a half-wavelength membrane between the transducer and the load in mechanically sectored ultrasonic scanners was investigated. In particular, the effects of impedance mismatch and detuning on broadband spectra were theoretically and experimentally studied. These studies indicate that for certain common cases, a bandwidth reduction of 20%–30% can be anticipated, resulting in a proportional decrease in the axial resolution.
High-frequency acoustic properties of a fluid/porous solid interface. II. The 2D reflection Green’s function
Authors: Feng Shechao , Johnson David Linton
Published: October 2005

A 2-D space–time reflection Green’s function is developed using the Cagniard–de Hoop technique for a fluid/lossless porous media planar interface configuration. It is then used to study the effects of the various surface waves whose velocities were calculated in the previous article. The time-dependent pressure response to a modeling source signal (Blackman–Harris pulse) for certain simulated experimental configurations is also presented. It is concluded that the amplitudes with which the new surface modes are generated are large enough to enable their detection.
T-matrix approach to study the vibration frequencies of elastic bodies in fluids
Authors: Peterson B. A. , Varadan V. V. , Varadan V. K.
Published: October 2005

The T matrix or null field method is used as a computational scheme for analyzing the scattering frequencies of a homogeneous elastic body in a fluid. These frequencies have a unique distribution, in the complex plane, for each body. We solve a scalar transcendental equation to find the scattering frequencies for a sphere. These frequencies are used as starting points in a matrix approach to find the scattering frequencies for a prolate spheriod. Lists and figures of the most important scattering frequencies for a sphere and a prolate spheroid are given.
Propagation of acoustic waves in a fluid-filled borehole surrounded by a concentrically layered transversely isotropic formation
Authors: Chan Andrew K. , Tsang Leung
Published: October 2005

The method of real axis integration is applied to compute the acoustic waveform due to a point source in a fluid-filled borehole surrounded by a concentrically layered transversely isotropic formation. The problem is of interest in acoustic logging because the earth, due to its intrinsic horizontally layering structure, is essentially a transversely isotropic medium. The presence of an invasion zone introduces concentric layering in the vicinity of the borehole. Due to the axial symmetry of the problem, only two characteristic waves are excited in the transversely isotropic medium. The effects of the anisotropy and concentric layering on the acoustic waveforms are studied.
Properties of acoustic and electromagnetic transmission coefficients and transfer matrices of multilayered plates
Authors: Scharnhorst Kurt P.
Published: October 2005

With the aid of certain symmetry properties of the elementary transfer matrices of acoustic and electromagnetic field vectors in single layers of absorbing materials, we derive the transformation properties of the system transfer matrices of bonded stacks of absorbing layers under the operation of reversal of the direction of incident radiation. While writing the energy transmission coefficients in such a way that the system transfer matrices appear explicitly, we apply their transformation properties to show that under certain circumstances these coefficients are invariant with respect to front and back surface illumination.
Effects of static and dynamic stress on the piezoelectric and dielectric properties of PVF2
Authors: Meeks Steven W. , Ting Robert Y.
Published: October 2005

The effects of hydrostatic pressure and pressure cycling on the piezoelectric properties of polyvinylidene fluoride (PVF2) have been experimentally investigated by using an acoustic reciprocity technique. The hydrostatic piezoelectric constants and the relative dielectric constant were measured as a function of pressure and pressure cycling for both voided and nonvoided PVF2 samples. The dynamic response of these materials to high-amplitude pressure pulses having a rise time of 1–3 ms was also determined. The results showed that the microvoid structures in PVF2 improve the material’s piezoelectric properties but at the same time increase its pressure dependence and introduce a hysteresis effect with changing hydrostatic pressure. Nonvoided PVF2 films were also shown to have a good dynamic response to pressure pulses and, therefore, are promising for applications such as underwater shock sensors.
Underwater sound generation by breaking wind waves
Authors: Kerman Bryan R.
Published: October 2005

The problem of identifying the source of wind-generated underwater sound is reviewed. Amalgamated observations of the ambient noise reveal a similarity structure, both in the acoustical spectrum and wind dependency, which allows for a considerable simplification of the problem. Mechanisms of sound generation are discussed with particular reference to oscillating bubbles. Air entrainment by breaking waves and the probabilistic distribution of bubbles are discussed. A model for underwater noise generation by bubbles oscillating in a breaking wave is proposed. It is argued that the most intense sound is associated with bubbles the radius of which is comparable to the Kolmogorov scale length. A slight three-eighths wind dependency is predicted for the frequency of the maximum intensity. Several arguments, one based on the number density of bubbles in a breaking wave, another based on the areal coverage of whitecaps, lead to the deduction that the sound intensity from a field of breaking waves varies as friction velocity to the three-halves power. Agreement in structure and order of magnitude is demonstrated.