bluuebunny/crossref_metadata_2025 huggingface dataset:
Signal detection in complex comodulated backgrounds by normal-hearing and cochlear-impaired listeners
Authors: Hall Joseph W. , Grose John H.
Published: October 2005

Comodulation masking release (CMR) was investigated in normal-hearing and cochlear-impaired listeners. The narrow-band masker centered on the tonal signal was flanked by a series of other narrow noise bands, some of which had temporal envelopes that were the same as that of the on-signal band (comodulated bands) and some of which had different temporal envelopes (codeviant bands). Previous research using such stimuli with normal-hearing listeners indicated that CMR was often substantially reduced when two codeviant bands were present at spectral locations close to the signal frequency, but that CMR recovered to some extent when more codeviant bands were added. In the present study, cochlear-impaired listeners showed an abnormally large reduction in CMR when codeviant bands were present, and poorer recovery of CMR with increasing number of codeviant bands. Supplementary experiments suggested that the poor recovery of CMR with increasing number of codeviant bands may have been due to the small range (in dB) over which CMR could occur in cochlear-impaired listeners. It is possible that abnormal reduction in CMR with codeviant bands present was due to poor peripheral analysis in hearing-impaired listeners.
Hearing threshold shifts from repeated 6-h daily exposure to impact noise
Authors: Hamernik Roger P. , Ahroon William A. , Davis Robert I. , Lei Sheau-Fang
Published: October 2005

Exposure of chinchillas to broadband, high-level impact noise on an interrupted 6-h daily schedule over 20 days has shown that pure-tone thresholds measured immediately following each daily exposure improve as much as 30 dB despite the continuing noise exposure. The time constant of this recovery effect (toughening) and the magnitude of the effect are related to the audiometric test frequency and the exposure energy. The trauma, quantified by permanent threshold shifts and sensory cell losses, produced by the interrupted exposure paradigm is generally less than that produced by an equal-energy uninterrupted exposure. The wide variations in the temporal pattern of threshold shift across similarly exposed animals suggest that the toughening effect reflects the underlying susceptibility of that animal to noise trauma.
The role of frequency resolution and temporal resolution in the detection of frequency modulation
Authors: Madden John P.
Published: October 2005

The experiment investigated subjects’ ability to detect short-duration changes in frequency. In an adaptive, 2AFC task, three normal-hearing subjects were asked to distinguish a sinusoidal signal that increased in frequency in a series of discrete steps from a standard that was identical except that its frequency increased essentially continuously. The signals were 60 ms in duration with center frequencies of 0.25, 0.5, 1, 2, 3, 4, and 6 kHz. The smallest frequency increase between steps (FI) at which the stepped signal could be distinguished from the standard was determined as a function of the number of steps in the signal. As the number of steps increased and the step duration decreased, the FI at first decreased and then reached a roughly asymptotic level. Eventually, however, at a certain number of steps, the FI increased rapidly. The data were analyzed using a model of auditory temporal resolution that included a bank of bandpass filters, a nonlinearity, a temporal integrator, and a decision device. The analysis yielded ERDs that ranged from 3.8 to 5.0 ms and did not change systematically with frequency. Detector efficiency varied considerably, being greatest at 0.5 and 1 kHz, and declining at higher and lower center frequencies.
Selective acoustic phonetic impairment and lexical access in an aphasic patient
Authors: Caplan David , Utman Jennifer Aydelott
Published: October 2005

The relationship between acoustic-phonetic disturbances and lexical access was explored in an aphasic patient. M.L. had a restricted disturbance of phonemic discrimination that affected the discrimination of voicing contrasts in nonword stimuli. Despite this impairment, her discrimination of voicing contrasts in words and her comprehension of auditorily presented words containing voiced segments was excellent. Performance on lexical decision was impaired: M.L.’s rejection of nonwords was poor and her reaction times and error rates for word stimuli showed a trend toward being influenced by the lexical status (word or nonword) of the item that would be formed by a change in voicing. The results are consistent with a role for a phonemic code in auditory word recognition, coupled with lexical-to-acoustic/phonetic feedback, but are also compatible with the view that other access codes for the Phonological Input Lexicon are also available.
Masking of speech by amplitude-modulated noise
Authors: Gustafsson Hans Å. , Arlinger Stig D.
Published: October 2005

The masking of speech by amplitude-modulated and unmodulated speech-spectrum noise has been evaluated by the measurement of monaural speech recognition in such noise on young and elderly subjects with normal-hearing and elderly hearing-impaired subjects with and without a hearing aid. Sinusoidal modulation with frequencies covering the range 2–100 Hz, as well as an irregular modulation generated by the sum of four sinusoids in random phase relation, was used. Modulation degrees were 100%, ±6 dB, and ±12 dB. Root mean-square sound pressure level was equal for modulated and unmodulated maskers. For the normal-hearing subjects, essentially all types of modulated noise provided some release of speech masking as compared to unmodulated noise. Sinusoidal modulation provided more release of masking than the irregular modulation. The release of masking increased with modulation depth. It is proposed that the number and duration of low-level intervals are essential factors for the degree of masking. The release of masking was found to reach a maximum at a modulation frequency between 10 and 20 Hz for sinusoidal modulation. For elderly hearing-impaired subjects, the release of masking obtained from amplitude modulation was consistently smaller than in the normal-hearing groups, presumably related to changes in auditory temporal resolution caused by the hearing loss. The average speech-to-noise ratio required for 30% correct speech recognition varied greatly between the groups: For young normal-hearing subjects it was −15 dB, for elderly normal-hearing it was −9 dB, for elderly hearing-impaired subjects in the unaided listening condition it was +2 dB and in the aided condition it was +3 dB. The results support the conclusion that within the methodological context of the study, age as well as sensorineural hearing loss, as such, influence speech recognition in noise more than what can be explained by the loss of audibility, according to the audiogram and the masking noise spectrum.
Measurements of ultrasonic pulse arrival time and energy level variations produced by propagation through abdominal wall
Authors: Hinkelman Laura M. , Liu Dong-Lai , Metlay Leon A. , Waag Robert C.
Published: October 2005

Ultrasonic pulse arrival time and energy level variations introduced by propagation through human abdominal wall specimens have been measured. A hemispheric transducer transmitted an ultrasonic pulse that was detected by a linear array transducer after propagation through an abdominal wall section. The array was translated in the elevation direction to collect data over a two-dimensional aperture. Differences in arrival time and energy level between the measured waveforms and calculated references that account for geometric delay and spreading were found. Plots of waveforms compensated for geometric path, maps of time delay differences and energy level fluctuations, and statistics derived from these for water paths and tissue paths characterize the measurement system and describe the time delay differences and energy level fluctuations caused by 14 different human abdominal wall specimens. Repeated measurements using the same specimens show that individual tissue path measurements are reproducible, the results depend on specimen position, and frozen storage of a specimen for three months does not appear to alter the time delay differences and energy level fluctuations produced by the specimen. Comparison of measurements at room and body temperature indicates that appreciably higher time delay differences occur at body temperature while energy level fluctuations and time delay difference patterns are less affected. For the 14 different abdominal wall specimens, the rms time delay differences and energy level fluctuations have average values of 43.0 ns and 3.30 dB, respectively, and the associated correlation lengths of the time delay differences and energy level fluctuations are 7.90 and 2.28 mm, respectively. The spatial patterns of time delay difference and energy level fluctuation in the reception plane appear largely uncorrelated, although some background variations in energy level fluctuation are similar to features in time delay difference maps. The results provide important new information about the variety and range of ultrasonic wave front arrival and energy variations caused by transmission through abdominal wall.
Acoustic streaming near a rigid sphere
Authors: Nyborg Wesley L.
Published: October 2005

It is shown for a flow field with vorticity, that even if the velocity u is axisymmetric, the term [(∇×u)⋅∇)]u is, in general, nonzero. In his treatment of acoustic streaming near a rigid sphere, Lane [J. Acoust. Soc. Am. 27, 1082 (1955)] dropped this term; this is probably why his results differ from those of others.
Absorption and velocity of ultrasound in binary solutions of poly (sodium 4-styrenesulfonate) and water
Authors: Esquivel-Sirvent R. , Yun S. S. , Stumpf F. B.
Published: October 2005

The absorption and velocity of ultrasound at 21 MHz and the shear viscosity were measured for water solutions of poly (sodium 4-styrenesulfonate) as a function of concentration and temperature. The molecular weight of the polymer is 70 000. The concentrations used were 1%, 5%, and 9% by weight, and the temperatures were 25, 30, 35, 40, and 45 °C. The absorption or α/f2 decreases almost linearly with increasing temperature at a given concentration and increases with concentration at a given temperature. The velocity is a linearly increasing function of the temperature and also increases with concentration at a given temperature. In addition, the shear viscosity decreases linearly with temperature and increases with concentration.
Acoustic imaging using ambient noise: Some theory and simulation results
Authors: Potter John R.
Published: October 2005

This article is concerned with the theory and simulation of passive imaging of quiet objects using the ambient noise field as illumination, a method known as ‘‘Acoustic Daylight.TM’’ A great body of work exists on active and passive acoustic systems, but the principle of using ambient noise as the sole illumination for acoustic imaging is almost unexplored. The possible performance envelope of an acoustic daylight system as a function of object shape, composition, degree, and orientation of anisotropy in the illuminating field is discussed. With such a large number of controlling variables a simple scattering model is required in the first instance for the problem to remain tractable. The theoretical development employs the Helmholtz–Kirchhoff integral with far-field approximations, evaluated by the stationary phase technique, which results in an analytical approximation for the energy density scattered near the specular angle by an object for a single source–object–receiver geometry. The expression is applied in a numerical implementation that sums over many sources and segments of a modeled object to give the total field. The model can be used for a wide range of object shapes and materials immersed in various ambient noise fields of practical interest. Some simulations of various objects in a homogeneous shallow-water duct are given. It is found that useful images can be formed provided either the ambient noise field is not isotropic in all three dimensions or the object is not perfectly reflecting.
Characteristics of photostrictively produced optoacoustic pulses
Authors: Dharamsi A. N. , Joshi R. P.
Published: October 2005

The characteristics of optoacoustic pulses produced by photostrictive means are investigated. Since such acoustic disturbances have a nonthermal origin, and can be as short as the inverse of the highest frequency phonons that couple the photostrictive deformation to the lattice, ultrashort (subpicosecond) optoacoustic pulses can be produced. The differences are discussed between cold photostrictive optoacoustic pulses and those produced by thermal means in terms of what may be called a rise time reduction factor that characterizes the relative pulsewidths of the thermal to nonthermal pulses; a criterion for picking materials that would show large rise time reduction factors is given. The strength of a photostrictive optoacoustic pulse, in the high-intensity regime, is calculated. Since the nonthermal nature of the photostrictive optoacoustic pulse is important in the production of ultrashort optoacoustic pulses, thermalization mechanisms subsequent to laser irradiation of the photostrictive material are examined. It is shown that there is a trade-off between the strength of the compression and the initial temperature that it exhibits, and an estimate of the expected initial temperature of the compression is given. The characteristics of photostrictively generated optoacoustic pulses and those produced by other means, including nonthermal electrostrictive generation, are compared.
Power flow analysis of surface waves on a cylindrical elastic shell in an acoustic fluid
Authors: Borgiotti Giorgio V. , Rosen Erik M.
Published: October 2005

It is known that an elastic cylindrical lossless shell immersed in an acoustic fluid can guide acoustic energy longitudinally without attenuation. In fact, for the physical and geometric parameters within suitable ranges, different surface wave modes, with different angular dependence around the cylinder, can be supported by the structure. These modes propagate longitudinally with subsonic phase velocities, and are evanescent in the transverse direction. The concomitant dispersion relationships, which provide the phase velocity versus frequency, are here established by using a thick shell model, in the form of a transverse resonance equation. Numerical results indicate that for frequencies greater than ka≥∼5 the surface wave propagation tends to become isotropic. This effect is manifested by the change of the shape of the dispersion curve, relating longitudinal and circumferential wave numbers which turns into a circle from the ‘‘figure 8’’ characteristic of the low-frequency regime. The intensity vector field in the fluid and in the shell are studied for different surface wave modes, at different frequencies with the aim of understanding the mechanism of the power flow. For the axisymmetric case it is found that in the lower portion of the frequency region of existence of the mode, the power flowing in the fluid is substantially larger than in the shell, whereas at higher frequency the situation is reversed. For nonaxisymmetric modes the power flow within the shell is higher than in the fluid with the exception of the n=1, mode for which in a limited frequency region the power transported within the fluid is slightly higher. Also for the intermediate frequency range, i.e., ∼2<ka<∼4, the power is transported via a shear and bending mechanism.
Acoustic radiation from periodic and sectionally aperiodic rib-stiffened plates
Authors: Cray Benjamin A.
Published: October 2005

The far-field and near-field solutions for the radiated acoustic pressure from a line-driven fluid-loaded, rib-stiffened thin elastic plate have been obtained. The plate has been configured to have two sets of rib stiffeners, though the formulation given has been extended to include additional rib-stiffener sets. The stiffeners composing a given set are identical and are spaced periodically with distance l. However, one set of stiffeners is shifted by an amount Δ from the other set. In this manner, portions of the plate may be configured with periodic repeating sections of arbitrary length l having aperiodic rib spacing. The stiffeners exert reactive forces upon the plate, but not angular moments. Fluid loading is included on the upper surface of the plate while the lower surface is unloaded, except for a time harmonic line force applied normal to the lower surface. The far-field radiated pressure has been obtained using the method of stationary phase. Numerical integration techniques were used to obtain the near-field acoustic pressure.
Fully three-dimensional exact and ray asymptotic formulation of the characteristic wave fields on a spherical shell surface
Authors: Ho J. M. , Felsen L. B.
Published: October 2005

Fully three-dimensional Green’s functions are important for synthesizing the acoustic scattering response from submerged spherical shells due to excitation not only by actual radiating sources without special symmetries but also by induced sources on the shell which can characterize the effects of truncations or loadings of the empty undisturbed shell prototype. As in a previous two-dimensional (2-D) study of scattering due to axisymmetric (azimuthally independent) source configurations [J. M. Ho and L. B. Felsen, J. Acoust. Soc. Am. 88, 2389–2414 (1990)], the goal is the derivation of self-consistent hybrid ray-mode asymptotic algorithms from appropriate rigorous alternative spectral representations; hybrid ray-mode algorithms have been shown to be well matched to the wave phenomena which generate the scattered acoustic fields in the fluid in the mid- and high-frequency range ka≳5, where k is the wave number in the fluid and ‘‘a’’ is the mean radius of the shell, and also under pulsed excitation. The presentation here deals with the rigorous spectral foundation, asymptotics, and ray-acoustic interpretation of the rich variety of generic 3-D wave phenomena encountered on the shell surface, which must be understood in order to treat the general case of arbitrary source and observer locations in a follow-up paper.
Phase variabilities and zeros in a reverberant transfer function
Authors: Tohyama Mikio , Lyon Richard H. , Koike Tsunehiko
Published: October 2005

The phase trend of a transfer function (TF) has a nearly constant group delay in a reverberant sound field under high modal overlap conditions. This phase trend is predictable from the number of nonminimum phase zeros of the TF. This paper investigates the phase variability from such a phase trend in a reverberant TF. These phase fluctuations, which are generally due to random occurrences of both poles and zeros, can be expressed using the group delay, which is the first derivative of the accumulated phase. Theoretical analysis of the group delay implies that its fluctuations have a ‘‘1/f’’ type of spectrum and that the variance of the group delay is independent of the frequency band and decreases as the damping of the system increases. The results are confirmed by the power spectrum and correlation analysis using measured TF records. Accumulated phase variances are also investigated on the basis of the Δ statistic [F. Dyson and M. Mehta, ‘‘Statistical Theory of the Energy Levels of Complex Systems. IV,’’ J. Math. Phys. 4, 701 (1963)]. The variances increase in linear proportion to the frequency interval of interest, as the frequency interval increases; however, they increase in proportion to the square of the frequency interval when the frequency interval is short.
Prediction and evaluation of the scattering from quadratic residue diffusers
Authors: Cox Trevor J. , Lam Y. W.
Published: October 2005

The scattering from quadratic residue diffusers has been predicted using methods based on the Helmholtz–Kirchhoff integral equation. The methods consisted of two boundary integral methods, and two more approximate solutions utilizing Kirchhoff’s boundary conditions. The predictions were compared to measurements made in both the near and far fields. An accurate boundary integral method which works below and above the well cutoff frequency has been found. The limitations of the more approximate methods have been defined. The approximations behind the quadratic residue diffuser’s design have been tested. The important assumption of a phase change local reacting admittance over each well face was found to be good over a wide range of frequencies. The frequency limit of this approximation has also been defined.
The use of image contrast and entropy criteria for the estimation of imaging parameters in acoustic microscopy
Authors: Douglas Bretton L. , Kent S. Davis , Lee Hua
Published: October 2005

Certain key acoustic imaging parameters such as target velocity and range, sound velocity, and sound attenuation, are often not available with precision. The images formed with erroneous parameters suffer from degradation in resolution and dynamic range. Objective criteria for evaluating the quality of acoustic images enable us to search the parameter space so that the optimal acoustic images can be formed. In this paper, two such criteria, image contrast and image entropy, are successfully applied to the estimation of the depth of features imaged in holographic acoustic microscopy.
Quantitative performance analysis of the phase-only technique for high-resolution acoustical imaging
Authors: Lee Hua
Published: October 2005

The phase-only technique is commonly used in holographic imaging. It utilizes only the phase information of the resultant complex wave field for image reconstruction. The amplitude information is either unavailable due to the limited data acquisition capability or removed for wave-field data compression purposes. From the perspective of signal processing, phase-only image formation is an extreme case of signal reconstruction from partial information. In the past, the capability of high-resolution imaging with only the phase information and the superior resolving capability over the counterpart, amplitude-only method have been demonstrated. However, the previous study was limited to several selected cases, and the resolution analysis was largely qualitative. It is highly desirable to conduct a quantitative performance evaluation and theoretical resolution analysis for the phase-only technique. Image reconstruction with partial wave-field information often involves nonlinearity because of the loss of wave-field information. Therefore, resolution analysis becomes a difficult task for the conventional measure. In this paper, the problem is approached with an alternative resolution formula and is extended to include the effects of wave-field information loss. As a result, it is now possible to quantitatively evaluate the resolving capability of the phase-only method. With this technique, one can also numerically compare the performance with that of the amplitude-only case, and theoretically support the experimental findings. In addition, this approach can also be applied to a quantitatively performance evaluation of various low bit-rate imaging schemes.
Beamforming with dense random arrays: The development of a spatially shaded polyvinylidene fluoride acoustic transducer
Authors: McGehee Duncan , Jaffe Jules S.
Published: October 2005

This article describes an approach to array design that results in the construction of transducers producing precisely controlled radiation patterns. The method of dense random arrays employs an array of equally weighted elements, randomly distributed with a density distribution that matches a desired shading. As the spatial density of elements increases, the theoretical radiation pattern approaches that of the ideal shading. If the ideal shading is real (e.g., for a symmetric beam), all elements in the random array will be either in phase or in phase opposition, and the array will require a single amplifier coupled with a phase inverter. If the ideal shading is both real and positive (e.g., Gaussian or Blackman–Harris shading), all elements will be in phase and will require only one amplifier. This approach was used to design a linear array to generate a 2° wide Gaussian beam. The elements had a minimum spacing of one-quarter of a wavelength and were placed using a Monte Carlo approach. A theoretical sidelobe level of −21.8 dB was achieved, with good agreement in the central beam (2.4° beamwidth predicted). A 500-kHz acoustic transducer with this element distribution was built using 110-μm-thick polyvinylidene fluoride (PVDF). Experiments reveal a radiation pattern very close to the predicted pattern, with −20.8-dB sidelobes.
A computational model of the auditory periphery for speech and hearing research. I. Ascending path
Authors: Giguère Christian , Woodland Philip C.
Published: October 2005

A dual analog/digital model of the ascending path through the entire auditory periphery is described. The analog representation consists in the concatenation of electrical circuit submodels for (a) the diffraction of the external ear system; (b) the propagation through the concha and auditory canal; (c) the transmission through the middle ear; (d) the basilar membrane motion and cochlear hydrodynamics; (e) the fast motile mechanism of the outer hair cells; and (f) the neural transduction process of the inner hair cells. Time-domain numerical solutions are obtained by applying the technique of wave digital filtering onto the resulting analog circuit. The present version of the model reproduces the sound pressure gain at the eardrum for lateral sound incidence, the vibration characteristics of the stapes, and the low-frequency attenuation provided by the stapedial muscle. Source elements in the cochlear module provide level-dependent basilar membrane tuning curves leading to dynamic compression of input signals near the characteristic frequency/place. The output is the tonotopic distribution of firing activity in the auditory nerve. A companion article addresses the modeling of the descending paths [C. Giguère and P. C. Woodland, J. Acoust. Soc. Am. 94, 343–349 (1993)].
A computational model of the auditory periphery for speech and hearing research. II. Descending paths
Authors: Giguère Christian , Woodland Philip C.
Published: October 2005

The auditory model described in Giguère and Woodland [J. Acoust. Soc. Am. 94, 331–342 (1993)] is applied to the simulation of the descending paths to the peripheral ear. An external feedback unit regulates the average firing rate of inner hair cell afferent fibers via a simplified modeling of the dynamics of the acoustic reflex to the middle ear and of the slow efferent innervation of the outer hair cells. The terminal effector of the acoustic reflex system is the stapedial muscle which stiffens the middle ear and reduces vibration of the stapes by up to 15 dB below 1000 Hz. The control function of the efferent system is realized by modulating the coupling gain between the inner hair cell cilia and the surrounding subtectoral fluid over a range of 24 dB. The efferent system has the capability to regulate firing rate over selective tonotopic regions of the auditory nerve. It operates at a lower target rate and has a faster response than the acoustic reflex system. The feedback unit leads to dynamic compression of speech cochleograms along both the time and frequency axes.
Modeling of a piezoelectric transducer and its application to full waveform acoustic logging
Authors: Kostek S. , Randall C. J.
Published: October 2005

A velocity-stress finite-difference (VS-FD) model is presented for a cylindrical piezoelectric transducer in a borehole. The borehole may be irregular and the surrounding formation inhomogeneous. The model is two dimensional in that azimuthal symmetry is assumed. The description of the tranducer is a full elasto-electromagnetic one, including transverse isotropy in the elastic, dielectric, and piezoelectric parameters, and dissipation in the piezoelectric material. The borehole propagation portion of the model is verified by comparison with a standard transform technique. Predictions of the model for a piezoelectric cylinder radiating into a fluid medium are compared to experimental results with excellent agreement. The radiation patterns of a bare transducer near resonance frequencies are found to be anisotropic. Acoustic waveforms in a borehole excited by a finite sized cylindrical transducer are displayed and are quite different from those excited by an ideal point pressure source. The effect of borehole loading upon the impedance of the transducer is shown to be small.
On the underwater acoustic field of a moving point source. I. Range-independent environment
Authors: Lim Paul H. , Ozard John M.
Published: October 2005

Hawker [J. Acoust. Soc. Am. 65, 675–681 (1979)] derived the acoustic field of a slowly moving point source with constant horizontal velocity in a uniform waveguide. The acoustic field for sources moving with arbitrary but small horizontal velocities, a more general result, is obtained in this paper. The wave equation is solved via a temporal Green’s function, and the ensuing acoustic field is naturally expressed in terms of retarded times familiar in relativity theory and electrodynamics. This contrasts sharply with conventional solutions in acoustics that are expressed in terms of contemporary time. For a given source motion, the solution may be recast entirely in terms of contemporary time. In the special case of a slowly moving source with constant horizontal velocity, the new solution reduces to that of Hawker. An example is given to illustrate the form of the new solution for a point source in circular motion in a horizontal plane.
Observations of underwater sound at frequencies below 1500 Hz from breaking waves at sea
Authors: Hollett Reginald D.
Published: October 2005

An experiment was performed to obtain underwater sound recordings at frequencies below 1500 Hz from a patch of sea surface in the presence of breaking waves, concurrently with video recordings of events in the patch. The sound recordings were obtained using a vertical array in end-fire mode. Some results are presented for wind speeds of 10 and 15 m s−1. The sound recordings consist of series of discrete bursts of sound, each burst lasting a few seconds. The stronger bursts are readily identified with breaking waves. The weaker bursts are attributed to smaller breakers obscured from view. The sound is generated during the breaking phase. The spectral components are observed at all frequencies down to 75 Hz (down to 50 Hz at times of less shipping). The increase in spectrum level is 10 to 15 dB. In general, the spectrum appears to evolve with the breaking phase, the higher frequency components arising first, at the onset of breaking, the lower frequency components arising a second or more after.
Simulation of acoustical and elastic waves and their interaction
Authors: Andreassen O/yvind , Lie Ivar
Published: October 2005

A method for numerical simulation of wave propagation through an interface separating two media, e.g., water and ocean bottom, is derived using Chebyshev spectral collocation. The propagation of acoustical waves in water is modeled by the Euler equations applied to a stratified fluid, while the elastic waves are modeled by the equations of linear elasticity. The transmission of the waves through the interface is based on the physical boundary conditions, continuous normal velocity component and normal stress, and implemented via characteristic boundary conditions. Domain decomposition procedures are used to solve the equations in each of the two physically different domains and to match the solutions at the boundary. At the interface modeling the ocean surface, free boundary conditions are used. The conditions at the lower and vertical boundaries are constructed to give free transmission of the wave modes, making no influence on the wave propagation. Some test cases are discussed, the simplest based upon a plane interface, the second with a piecewise linear interface made up of a horizontal and an inclined part.
Optimization of hydrophone placement for acoustic arrays using simulated annealing
Authors: Hayward Thomas J.
Published: October 2005

The simulated annealing technique of nonlinear optimization [S. Kirkpatrick, C. D. Gellatt, Jr., and M. P. Vecchi, Science 220, 671–680 (1983)] is applied to optimization of horizontal and vertical sonar receiver array configurations. Optimizations of horizontal planar arrays to minimize array noise gain in a 2-D isotropic noise field result in regular geometric arrangements of the array elements. Performance measures are then formulated for arbitrary 3-D array configurations using either plane-wave beamforming or linear matched-field beamforming. These measures, which are based on normal-mode modeling of average array signal and noise responses, are applied first to optimization of plane-wave–beamformed vertical arrays. The optimized vertical-array configurations exhibit less regularity of spacing than do the horizontal arrays, because of the complexity of the acoustic field in the vertical. The results can be interpreted as a compromise between placement of hydrophones at depths with high signal-to-noise ratio and separation of hydrophones to reduce the array noise gain. Examples are given for optimization for matched-field processing based on minimization of average array noise power or average sidelobe power.
Stability of determination of composite moduli from velocity data in planes of symmetry for weak and strong anisotropies
Authors: Chu Y. C. , Rokhlin S. I.
Published: October 2005

The determination of elastic constants from ultrasonic bulk wave velocity data taken in a plane of symmetry is studied. It is shown that the problem is well-posed, i.e., the solution is unique and stable. The displacement polarization factors are used to define the degree of material anisotropy and represent solutions of the Christoffel equation. Such a representation in a rotated coordinate system helps to derive simple expressions for coefficients describing the sensitivity of ultrasonic waves to different elastic constants. Thus the optimal refraction angles for velocity measurement can be determined simply. The analysis performed shows that the elastic constants reconstructed from velocity data are not affected by the selection of initial guesses used in a nonlinear least-square optimization (the solution is unique). The solution stability is validated by performing reconstruction with different levels of random scatter in the velocity data. The effect of the angle range used for velocity measurements has been analyzed, and it is shown that, depending on the refraction-angle range, reconstruction of the longitudinal elastic constants is dominated either by the quasilongitudinal or by the quasitransverse velocity. The desirable range of refraction angles for determination of elastic constants with high accuracy is determined.
The scattering of an acoustic wave from the absorbing-elastic coupling of two half-planes
Authors: Asghar S. , Hussain Akhtar , Ahmad Bashir
Published: October 2005

The scattering of an acoustic wave from an absorbing half-plane coupled with an elastic half-plane is considered. The planes are subjected to heavy-fluid loading where the coupling between the fluid and the plate motions is significant. It is observed that the scattered field consists of a subsonic surface wave (Biot–Stoneley wave) traveling along the elastic plate and an edge diffracted wave. The effect of absorption on the scattered field is shown explicitly in terms of the absorbing parameter.
Weakly nonlinear waves and acoustic streaming produced by an oscillating rigid cylinder
Authors: Furuyama Shinji , Inoue Yoshinori
Published: October 2005

The weakly nonlinear propagation of waves radiated from a rigid cylinder executing harmonic translatory oscillations in a direction perpendicular to its axis into an ideal gas is studied theoretically, under the condition that an acoustic Reynolds number is sufficiently large. The entire propagation process, from generation of sound to the stage where the wave amplitude is saturated, is analyzed in the leading order approximation. It is shown that in the near-field acoustic streaming occurs around the cylinder in the next order. The compressibility in fluid together with the nonlinearity plays an essential role in this acoustic streaming. For the problem up to the shock formation a far-field equation is exactly solved and the subsequent evolution into the sawtooth wave is examined using the equal-areas rule. These multidimensional waves have the directional quality proportional to cos θ (θ is the angle measured from the direction of oscillation of the cylinder). At a great distance it appears that the saturation of the wave and the amplitude simultaneously becomes independent of cos θ there.
An optimal absorbing boundary condition for finite difference modeling of acoustic and elastic wave propagation
Authors: Peng Chengbin , Toksöz M. Nafi
Published: October 2005

This paper presents an optimal absorbing boundary condition designed to model acoustic and elastic wave propagation in two-dimensional and three-dimensional media using the finite difference method. In this condition, extrapolation on the artificial boundaries of a finite difference domain is expressed as a linear combination of wave fields at previous time steps and/or interior grids. The acoustic and elastic reflection coefficients from the artificial boundaries are derived. They are found to be identical to the transfer functions of two cascaded systems—the inverse of a causal system and an anticausal system. The method makes use of the zeros and poles of reflection coefficients in a complex plane. The optimal absorbing boundary condition described in this paper yields, on the average, reflection coefficients about 10-dB smaller than Higdon’s absorbing boundary condition, and about 20-dB smaller than Reynolds’ absorbing boundary condition.
Acoustic scattering from an air-filled cylindrical shell with welded flat plate endcaps: Experimental and theoretical study
Authors: Lecroq F. , Maze G. , Décultot D. , Ripoche J.
Published: October 2005

Many authors have already studied the acoustic scattering from infinite cylinders or cylindrical shells both theoretically and experimentally. When the shells are insonified in a direction perpendicular to its axis, some circumferential waves propagate. When the insonification is not perpendicular to the axis of the shell, some helical waves propagate. In this paper, the influence of the length limitation of the shell on the different waves which propagate around the shell is studied. In the frequency range used in this work with a normal insonification, there was no difference between an infinite and a finite length shell. With an oblique incidence (10°), there were several resonances with the same vibration mode n but with different frequencies that were close to each other. A calculation, described in this paper, explains these phenomena.
A time-domain backpropagating ray technique for source localization
Authors: Voltz Peter , Lu I-Tai
Published: October 2005

A new method is presented for source localization which is based on a ray backpropagation procedure, and which exploits both the temporal and spatial characteristics of the multipath arrival structure at a receiving sensor array. The basic method consists of two steps. The first step employs a receiving sensor array to estimate the angles and relative arrival times of the various multipath trajectories which arrive at the receiver after having been emitted by the source located at an unknown range R and depth Z from the receiver. The second step utilizes a ray tracing technique to backpropagate the rays and produce an estimate of the source position by making full use of all the spatial and temporal information extracted by the array. The source signal is taken to be a narrow-band stochastic process, which simulates a realistic situation commonly encountered in the ocean acoustic environment. Some key advantages of the approach are (1) localization ambiguity is minimized by utilizing ray travel times as well as path convergence; (2) the approach does not require full-wave matched-field processing; (3) ray backpropagation is numerically very efficient; (4) phase ambiguity is eliminated by employing the group delay of arriving wave packets; (5) ray chaos can be avoided simply by excluding chaotic rays from the backpropagation algorithm.
Effects of anneal upon transmission loss and mode group velocity in polycrystalline metal wires
Authors: Nicholson N. C. , McDicken W. N. , Watson L. M. , Jervis J.
Published: October 2005

Relative transmission coefficients of pulses of ultrasound, over the frequency range 1.0–5.0 MHz, propagating in cold-drawn and heat-treated wires of aluminum, stainless steel, brass, and copper are compared. Various heating cycles were used to alter the structure of the grains in the wires and particularly the grain size itself. It was found almost without exception that starting from an initially cold-worked sample of wire, ultrasound transmission first of all decreased with heat treatment; then, as the grains started recrystallizing, ultrasound transmission increased, reaching a maximum at complete recrystallization, and thereafter decreased once again with the process of grain growth. The change in ultrasound transmission with heat treatment was most noticeable at higher frequencies, with a dramatic increase in transmission loss for wires subjected to extensive amounts of heat treatment. During the investigation it was discovered that, contrary to expectation, group velocities of modes propagating in stainless-steel wires were dependent upon the amount of heat treatment that the wires had been subjected to. Further study revealed that group velocities of modes propagating in brass wires were similarly affected by heat treatment. In particular, the lowest longitudinal mode which is predicted by Pochhammer’s theory to be equal to the bar velocity at the lower end of its frequency range, increased with amount of heat treatment and approached the dilatational velocity. No such marked changes were observed in the pure metal wires studied.
Electrostrictive ceramics for underwater transducer applications
Authors: Rittenmyer Kurt M.
Published: October 2005

The electromechanical properties of two electrostrictive materials designed for use in underwater acoustic applications are determined as functions of temperature and electric field. The materials are 0.859 Pb(Mg1/3Nb2/3)O3–0.141 PbTiO3 doped with 2.5% SrTiO3 or BaTiO3. Dielectric properties are determined as functions of temperature and electric field. The equivalent piezoelectric coefficients were found as functions of temperature to be equal to or superior to the lead zirconate–titanate ceramics at very modest dc bias fields (2 kV/cm) at temperatures in the range from 10 to 35 °C. Outside of this temperature range, the piezoelectric and dielectric coefficents decrease rapidly. Electromechanical losses were found to be sufficiently small for the SrTiO3 composition but not the BaTiO3 composition.
Diffuse waves on submerged thin shells
Authors: Weaver Richard L.
Published: October 2005

A statistical energy method is proposed for the calculation of the acoustic power and radiation pattern shed from diffusely vibrating thin-walled submerged shells. It is presumed that, at frequencies below coincidence where flexural waves cannot efficiently radiate into the fluid, radiation is dominated by the weakly fluid-coupled longitudinal and shear waves, which couple to the fluid by means of curvature and the Poisson effect. Assumed equipartition of acoustic energy amongst flexural, shear and extensional modes, and eikonal approximation calculations of the radiation rate from each mode type results in estimates for the diffuse radiation rate from a submerged shell. These rates are found to be largely independent of details of the structure and are very small, with loss tangents (Im{ω}/Re{ω}) of the order of 10−4. This is contrasted with the much larger loss tangents which are obtained at frequencies above coincidence.
Maximum likelihood estimation of the locations of multiple sources in an acoustic waveguide
Authors: Mirkin Adam N. , Sibul Leon H.
Published: October 2005

The deterministic maximum likelihood (ML) estimator is applied to the problem of estimating the locations of multiple sources in an acoustic waveguide. The structure of the estimator is examined for different noise fields, and the alternating maximization algorithm is proposed as an efficient method for its implementation. Asymptotic expressions for the estimators performance are presented and studied in detail for the special cases of one and two sources. The results of numerical simulations verifying these expressions and comparing the estimator’s favorable performance to that of the minimum variance distortionless response method are presented.
The effect of nonsimultaneous on-frequency and off-frequency cues on the detection of a tonal signal masked by narrow-band noise
Authors: Bernstein Leslie R. , Trahiotis Constantine
Published: October 2005

Listeners’ detection thresholds were measured for a 125-ms, 1-kHz tonal signal masked by a similarly gated 50-Hz-wide band of noise. A two-interval, adaptive, forced-choice procedure either with or without temporally surrounding cuing intervals containing 50-Hz-wide bands of noise was employed. When the cues were present, their center frequency was either 1 kHz (on-frequency) or 900 or 700 Hz (off-frequency). In the conditions of principal interest, the envelopes and phase modulations of the bands of noise were ‘‘frozen’’ across the four intervals that defined a trial, but were chosen randomly across trials. Thresholds were lowest with cues centered at 1 kHz and increased substantially when the center frequency of the cues was changed to 900 or 700 Hz. With cues centered at 700 Hz, performance was equivalent to that obtained without cues and with the masking noise ‘‘frozen’’ across the two intervals that defined a trial. A similar pattern of results was obtained with high-frequency stimuli, where sensitivity to fine-structure information is greatly reduced. Roving the level of the stimuli over a 40-dB range generally reduced sensitivity but did not greatly affect the overall pattern of the data. Thresholds obtained in the two-interval task with masking waveforms chosen randomly were compared with thresholds obtained when the masking waveform was ‘‘frozen’’ within, but not across trials. Differences in threshold appeared to be accounted for by the listeners’ use of changes in the mean slope of the envelope of the noise produced by adding the tonal signal.