bluuebunny/crossref_metadata_2025 huggingface dataset:
Attenuation, dispersion, and anisotropy by multiple scattering of transmitted waves through distributions of scatterers
Authors: Groenenboom Jeroen , Snieder Roel
Published: October 2005

Scattering of waves causes the coherent wave field to be attenuated and dispersed. These phenomena express the fact that the pulse loses coherence by which incoherent coda energy is created. First-order scattering theory violates the law of energy conservation and therefore cannot be used when the wave field is strongly distorted. An approximation is proposed which estimates the interaction between different scatterers by considering only multiple forward scattering interactions. Internal of a single scatterer all multiple interactions are maintained. This approximation can only be valid for the first part of the wave field and sufficiently weak scattering conditions. The heterogeneous medium can then be described as an effective medium that is a function of the scatterer density and forward scattering amplitude and the background medium. Simulations of the multiple scattering process with isotropic scatterers in two dimensions show that the discrepancies between the exact and approximate solution are small compared to the difference with the undisturbed wave field, even when the pulse is severely attenuated. Contrary to single scattering theory multiple scattering maintains the propagation of a stable and localized coherent wave. Apparently the nonlinear multiple scattering interactions cause a tendency for the coherent wave field to become insensitive to the specific scatterer distribution.
Scholte wave diffraction by a dihedral: Study at oblique incidence
Authors: Duflo Hugues , Tinel Alain , Duclos Jean , Lebeau Gilles
Published: October 2005

The geometrical theory of diffraction established by Keller allows one to describe the interaction between a bulk wave and a dihedral edge. It is experimentally verified that Keller’s laws are also valid to describe the interaction of a surface wave (the Scholte–Stoneley wave) with the edge of an elastic dihedral. The diffracted energy is on Keller’s cone.
Traveling-wave decomposition of surface displacements associated with scattering by a cylindrical shell: Numerical evaluation displaying guided forward and backward wave properties
Authors: Kaduchak Gregory , Marston Philip L.
Published: October 2005

Internal displacements of spherical shells subjected to steady sound waves in water have previously been computed by other researchers [e.g., R. Hickling et al., J. Acoust. Soc. Am. 92, 499 (1992)]. Such displacements can be perplexing to directly interpret with a guided wave representation because of the superposition of counterpropagating waves in a steady-state analysis. In this research the surface displacements of a cylinder were evaluated since they can be mathematically decomposed into counterpropagating circumferential traveling waves. (Unlike an analogous decomposition for spheres, the traveling-wave amplitudes in the cylinder case are regular at 0 and 180 deg.) By limiting attention to the radial displacements of the outer surface, it was also possible to display the response to short-tone bursts and thereby distinguish between counterpropagating wave packets. Both the steady-state and burst response situations clearly manifest waves launched on the shell. Shells studied include 2.5% and 10% thick SS304 shells with coincidence frequency excitations of the subsonic a0− Lamb wave and high-frequency (near kLh≊π) excitation of a negative group velocity Lamb wave.
Acoustic scattering from a sphere of small radius coated by a penetrable one
Authors: Kakogiannos Nikolaos B. , Roumeliotis John A.
Published: October 2005

The scattering of a plane acoustic wave from an impenetrable or a penetrable sphere of acoustically small radius coated by another penetrable sphere, is considered in this work. The method of separation of variables is used, combined with translational addition theorems for spherical wave functions. Analytical expressions are obtained for the scattered pressure field and the various scattering cross sections. Numerical results are given for various values of the parameters and for both an impenetrable or a penetrable inner sphere.
Effective measures for nonstationary microscale stiffness variation using multiresolution decomposition
Authors: Steinberg Ben Zion , McCoy John J.
Published: October 2005

Using the recently developed theory of multiresolution decomposition, a self-consistent formulation that governs the macroscale response of a linear dynamical system with nonstationary, microscale, stiffness heterogeneity is developed. The effects of the stiffness microstructure on the macroscale response are expressed via an across-scales coupling operator that can be interpreted as an effective large-scale measure of the material properties. It is shown that a stiffness microstructure can significantly affect a macroresponse. The effective properties are studied in the limit of a widely separated scales via general asymptotic considerations and specific numerical examples.
Comments on ‘‘Sound scattering by cylinders of noncircular cross section: A conformal mapping approach’’ [J. Acoust. Soc. Am. 96, 3064–3079 (1994)]
Authors: Laura Patricio A. A.
Published: October 2005

The authors have developed an extremely important method for predicting the far-field scattered pressure due to a plane wave incident upon an infinitely long cylinder of noncircular cross section. The method requires conformal transformation of the exterior and interior of a closed surface into a semi-infinite strip. The present letter discusses pertinent references dealing with (i) numerical methods for determining conformal mapping expressions and (ii) applications of the conformal mapping approach to acoustics situations.
Effect of random sea surface and bottom roughness on propagation in shallow water
Authors: Rouseff Daniel , Ewart Terry E.
Published: October 2005

The potential difficulties associated with modeling acoustic propagation in shallow-water environments are well documented. Larger scale deterministic features combine with random fluctuations in the water column, sediment, sea surface, and water–sediment interface to produce an extremely complicated propagation regime. The extent to which each of these factors needs to be included in realistic propagation modeling remains to be quantified. Toward this end, results from a series of detailed simulations generated using the parabolic equation method are presented. Beginning with a deterministic downward refracting sound-speed profile and a known sloping bottom, realizations of the random features are sequentially added to the simulation. Wind-driven surface gravity waves and power-law bottom roughness are considered. The individual and cumulative effects of these scattering mechanisms on the acoustic wavefront are quantified. Successive interactions with the random interfaces are studied. A modal decomposition reveals evidence of significant mode coupling. Temporal fluctuations in the acoustic wave are related to the time evolution of the sea surface.
Sound generation by a vortex ring collision
Authors: Tang S. K. , Ko N. W. M.
Published: October 2005

A collision between two vortex rings and its sound generation is studied numerically using the contour dynamics method. Results suggest that the radial acceleration and the rate of change of the axial acceleration of the vortex rings are the more important dynamic parameters for sound generation during the interaction. The former is important at or near the pass-through instant when the vortex rings are coplanar and are of unequal strength. The latter, being important in the sound generation during a head-on collision before the vortex ring cores are very close to each other, especially when the rings are thin, is also important in sound generation by an unequal strength vortex ring collision after the pass through when the vortex cores are separated by a distance so that the mutual induction strength does not result in significant change of the impulse of the stronger ring.
A head and transducer support system for making ultrasound images of tongue/jaw movement
Authors: Stone Maureen , Davis Edward P.
Published: October 2005

A head and transducer support system (HATS) was developed for use in ultrasound imaging of tongue movement. Ultrasound is an imaging technique that captures tongue motion during speech and thus has great appeal as a tool for speech research. However, because ultrasound systems are designed for clinical use, the transducer is hand-held and it is almost impossible to hold it completely steady under the chin when collecting tongue data. A system was needed to fix the head and support the transducer under the chin in a known position without disturbing speech. The HATS system was designed, constructed, and modified to provide valid, reliable tongue movement data by (1) immobilizing the head and (2) positioning the ultrasound transducer in a known relationship to the head.
Growth of low-pass masking of pure tones and speech for hearing-impaired and normal-hearing listeners
Authors: Dubno Judy R. , Ahlstrom Jayne B.
Published: October 2005

Tonal thresholds and consonant recognition were measured in low-pass maskers as a function of masker bandwidth and spectrum level. Thresholds and consonant-recognition scores were obtained for normal-hearing subjects, and for pairs of normal-hearing subjects (who listened in threshold-equating background noise) and hearing-impaired subjects. Consonant-recognition scores were compared to scores predicted by a modified articulation index. Mean thresholds measured in low-pass maskers were higher for hearing-impaired than for normal-hearing subjects for signal frequencies above the masker. Slopes of functions relating thresholds for signals above the masker to masker spectrum level were not significantly different between hearing-impaired and normal-hearing subjects listening in spectrally shaped broadband noise (SSBB), but were shallower than slopes of masking functions for normal-hearing subjects listening without SSBB. Slopes of masking functions for signals within the masker were equivalent for all subjects. Slopes of functions relating consonant recognition to masker spectrum level were similar within subject pairs, whereas, in some cases, slopes of functions relating consonant recognition to speech level were shallower for hearing-impaired subjects than for their normal-hearing counterparts. Although greater improvement in consonant recognition with speech level was predicted for hearing-impaired than for normal-hearing subjects, on average, less improvement with speech level was observed. Shallower slopes of functions relating score to speech level observed for some hearing-impaired listeners may result from more shallow growth of speech sensation levels in spectral regions above the low-pass masker.
On measuring psychometric functions: A comparison of the constant-stimulus and adaptive up–down methods
Authors: Dai Huanping
Published: October 2005

Psychometric functions were obtained using the conventional constant-stimulus method and an adaptive up–down method, for both computer-simulated and human observers. Except when the stimuli are closely placed, psychometric functions obtained with the adaptive method are as accurate as those obtained with the constant-stimulus method. Empirically, the adaptive method has some potential advantages owing to its ability to automatically concentrate the trials within the dynamic range of the psychometric function. It needs no pilot measurements for setting the signals as required by the constant-stimulus method. Furthermore, following a marked change in the underlying psychometric function, the distribution of the trials is automatically readjusted. Thus, on the basis of empirical considerations, the adaptive method is a better choice than the constant-stimulus method for measuring psychometric functions.
Lateralization of comodulated complex waveforms
Authors: Saberi Kourosh
Published: October 2005

This study examines the ability to lateralize a complex signal characterized by correlated temporal activity across widely separated frequency regions. The high-frequency complex consisted of two narrow-band stimuli. The two stimuli had common interaural delays but different carriers centered on nonoverlapping critical bands. Two basic conditions were examined: The narrow-band stimuli had temporal envelopes which were (1) identical or (2) different. In the first experiment, narrow bands of noise were used which either had identical temporal envelopes (comodulated) or statistically independent envelopes (CFs=2550 and 3350 Hz). In the second experiment, two sinusoidally amplitude-modulated (SAM) tones were used whose modulators either had the same starting phase or a different starting phase (CFs=2550 and 4000 Hz). Results of the first experiment showed that for bandwidths narrower than 300 Hz, comodulated bands produced significantly lower interaural-delay thresholds compared to independent bands. Results of the second experiment showed that when the two SAM tones (100-Hz modulation rate) had the same modulator starting phase, interaural-delay thresholds were lowest.
Villchur revisited: Another look at automatic gain control simulation of recruiting hearing loss
Authors: Duchnowski Paul , Zurek Patrick M.
Published: October 2005

An algorithm to simulate the effects of sensorineural hearing impairment on speech reception was investigated. Like that described by Villchur [J. Acoust. Soc. Am. 62, 665–674 (1977)], this simulation employs automatic gain control in independent frequency bands to reproduce the elevated audibility thresholds and loudness recruitment that are characteristic of this type of loss. In the present implementation, band gains are controlled in an effort to simulate loudness recruitment directly, using recruitment functions that depend only on the magnitude of hearing loss in the band. In a preliminary evaluation, two normal-hearing subjects listened to the simulation matched to hearing losses studied previously [Zurek and Delhorne, J. Acoust. Soc. Am. 82, 1548–1559 (1987)] with noise-masking simulations. This evaluation indicated that the present automatic gain control simulation yielded scores roughly similar to those of both the hearing-impaired listeners and the masked-normal listeners. In the more-detailed evaluation, the performance of three listeners with severe sensorineural hearing loss on several speech intelligibility tests was compared to that of normal-hearing subjects listening to the output of the simulation.

These tests included consonant–vowel syllable identification and sentence keyword identification for several combinations of speech-to-noise ratio, frequency-gain characteristic, and overall level. Generally, the simulation algorithm reproduced speech intelligibility well, though there was a clear trend for the simulation to result in better intelligibility than observed for impaired listeners when high-frequency emphasis placed more of the speech spectrum above threshold at higher frequencies. Also, the hearing-impaired listener with the greatest loss showed the largest discrepancies with the simulation. Overall, however, the simulation provides a very good approximation to speech reception by hearing-impaired listeners. The results of this study, together with previous studies of noise-masking simulation, suggest that threshold elevation and recruitment, which are necessary features of a simulation of cochlear hearing loss, can also be largely sufficient for simulating the speech-reception performance of listeners with moderate to severe hearing impairments.
Effect of release time in compression hearing aids: Paired-comparison judgments of quality
Authors: Neuman Arlene C. , Bakke Matthew H. , Mackersie Carol , Hellman Sharon , Levitt Harry
Published: October 2005

Paired-comparison judgments of quality were obtained from 20 hearing-impaired listeners for speech processed through simulated compression hearing aids varying in release time (60, 200, 1000 ms) at three different compression ratios (1.5, 2, 3:1) and for three different background noises (ventilation, apartment, cafeteria). Analysis revealed that the main effect of release time did not have a significant effect on perceived quality. The interaction between release time and noise type was found to be significant. While no significant difference in preference for release times was evident for the ventilation noise, the longer release times (200 and 1000 ms) were preferred for the higher level noises (apartment noise, cafeteria noise). Post hoc testing revealed that the mean preference scores for the 200- and 1000-ms release time were significantly greater than that of the 60-ms release time with the competing cafeteria noise (p<0.05). Analysis of individual subject data revealed statistically significant preferences that differed from the group mean, suggesting that individualized fitting of this parameter of a compression hearing aid might be warranted.
Vibrotactile forward masking: Effects of the amplitude and duration of the masking stimulus
Authors: Gescheider G. A. , Santoro K. E. , Makous James C. , Bolanowski S. J.
Published: October 2005

Tactile thresholds for detecting a 50-ms signal presented 25 ms after the termination of a masking stimulus increased as a function of the amplitude level and duration of the masking stimulus. The effects were similar in both the P and NP I channels measured at 250 and 20 Hz, respectively. It was concluded that the increased masking caused by increasing the duration of the masking stimulus resulted from processes other than or in addition to temporal integration—the latter being a characteristic of the P, but not the NP I, channel. The slopes of the masking functions, in which threshold shifts were plotted as a function of masking-stimulus sensation level, were consistently greater for 20-Hz than for the 250-Hz stimuli, suggesting that masking efficiency is greater in the NP I than in the P channel.
Effects of ear-canal standing waves on measurements of distortion-product otoacoustic emissions
Authors: Whitehead M. L. , Stagner B. B. , Lonsbury-Martin B. L. , Martin G. K.
Published: October 2005

At frequencies above 3 kHz, standing waves in the ear canal complicate calibration of stimulus sound-pressure levels (SPLs) for measurements of distortion-product otoacoustic emissions (DPOAEs). In the literature, two stimulus-presentation strategies have been used for DPOAE measurements. In the ‘‘in-the-ear adjustment’’ strategy, the voltage command to the speakers is adjusted to maintain a constant stimulus SPL across frequency at the DPOAE-measurement microphone. In the ‘‘iso-voltage’’ strategy, the voltage presented to the speakers is held constant across frequency, on the basis of the assumption that the frequency response of the speakers is approximately flat at the eardrum in the average human ear canal. Because of standing-wave effects, there are large, systematic but idiosyncratic differences of stimulus SPL between the two strategies. DPOAE-versus-frequency functions (‘‘DPOAE audiograms’’) obtained using both stimulus-presentation strategies in the same ears are presented. The differences of stimulus SPL between the two strategies, and the associated differences of DPOAE amplitude, are described and quantified. Around frequencies of standing-wave minima at the DPOAE probe, the in-the-ear adjustment strategy resulted in smaller DPOAEs at high L1=L2, but much larger DPOAEs at low L1=L2, than did the iso-voltage strategy. For any L1, the DPOAE-amplitude differences between the two strategies varied systematically with L1−L2. At the stimulus levels used to construct previously published population norms for clinical applications (i.e., L1≥65 dB SPL), there are only small differences of mean DPOAE amplitudes, and of the standard deviations of these means, between the two strategies.
Distortion-product otoacoustic emissions in Mongolian gerbils with resistance to noise-induced hearing loss
Authors: Boettcher Flint A. , Schmiedt Richard A.
Published: October 2005

Distortion-product otoacoustic emissions (DPOAEs) and the endocochlear potential (EP) were recorded in adult Mongolian gerbils exposed to noise for either 1 or 12 days. The exposure was an octave band of noise centered at 4 kHz at 80 dB SPL with a duty cycle of 6 h on, 18 h off. A previous study showed that a single such exposure causes 20–50 dB of temporary threshold shift (TTS) in the neural response at 4–8 kHz, but that the TTS is reduced to less than 10 dB following 12 daily exposures [Boettcher, J. Acoust. Soc. Am. 94, 3207–3214 (1993)]. This reduction in TTS is commonly referred to as resistance to noise-induced hearing loss (NIHL). To further analyze whether resistance to NIHL is caused by changes in the outer hair cell (OHC) system or the lateral wall system (or both), DPOAEs and EPs were measured in the exposed ears. The amplitudes of DPOAEs were significantly reduced in the frequency region from 4 to 10 kHz in subjects exposed to noise for 1 day, but were relatively normal in subjects exposed for 12 days. DPOAE amplitudes from frequency regions below the spectrum of the exposure were similar across the exposure and control groups except at the low-frequency edge of the noise where DPOAE amplitudes were consistently higher than normal in the exposed animals. The EP values in both exposure groups were not reduced from normal, unexposed levels. Thus there was no causal relationship between changes in the EP and the reduction of the DPOAE amplitudes. These data suggest that the development of resistance to noise is related to an initial depression of OHC activity followed by a recovery of activity to a stable level, despite an ongoing exposure.
Rate representation and discriminability of second formant frequencies for /ε/-like steady-state vowels in cat auditory nerve
Authors: Conley Ruth A. , Keilson Suzanne E.
Published: October 2005

Alternate forms of the steady-state vowel /ε/ with second formant peaks located at 1400, 1500, 1700, and 2000 Hz were used to study the representation and discrimination of second formant frequencies at the level of the auditory nerve. Recordings from large populations of auditory nerve fibers in response to these stimuli were used to create rate-place plots, which show second formant peaks that resembled the stimulus spectra. Measures of the peak amplitude decreased as sound level was increased and as second formant frequency was lowered. Representation of the spectra was degraded at the higher sound level because of saturation and two-tone suppressive effects. However, formant peaks were clearly represented in plots of rate differences between two vowels. Such plots resemble the ratio of the magnitudes of the two vowel spectra. The results suggest that information concerning the position of formant peaks is present in the average discharge rate of the auditory nerve. A measure of discriminability, d′, between vowel pairs was also calculated. Second formants differing by 125–240 Hz can be discriminated using the rate responses of individual fibers that are optimally placed on the basilar membrane; the estimated second formant jnd for the whole auditory nerve is approximately 1 Hz.
Analog neural network-based helicopter gearbox health monitoring system
Authors: Monsen Peter T. , Dzwonczyk Mark , Manolakos Elias S.
Published: October 2005

The development of a reliable helicopter gearbox health monitoring system (HMS) has been the subject of considerable research over the past 15 years. The deployment of such a system could lead to a significant saving in lives and vehicles as well as dramatically reduce the cost of helicopter maintenance. Recent research results indicate that a neural network-based system could provide a viable solution to the problem. This paper presents two neural network-based realizations of an HMS system. A hybrid (digital/analog) neural system is proposed as an extremely accurate off-line monitoring tool used to reduce helicopter gearbox maintenance costs. In addition, an all analog neural network is proposed as a real-time helicopter gearbox fault monitor that can exploit the ability of an analog neural network to directly compute the discrete Fourier transform (DFT) as a sum of weighted samples. Hardware performance results are obtained using the Integrated Neural Computing Architecture (INCA/1) analog neural network platform that was designed and developed at The Charles Stark Draper Laboratory. The results indicate that it is possible to achieve a 100% fault detection rate with 0% false alarm rate by performing a DFT directly on the first layer of INCA/1 followed by a small-size two-layer feed-forward neural network and a simple post-processing majority voting stage.
Sound-pressure response measurement in small rooms over a finite region
Authors: Peacock Gavin R. , Bean Colin , Ellacott S. W.
Published: October 2005

Microphone measurement of sound-pressure response in rooms can give signals that are specific to the position at which it is taken. A measurement responsive to a region about the measurement position can easily be gained by taking several pressure readings. The challenge is to obtain such an average while limiting the number of measurement positions. The advantages of such a measurement are given. The problem is defined fully in terms of source and target signals. The use of theory as a relating medium between source and target is discussed and rejected. The use of neural networks is introduced as a relating medium capable of learning from example. Some provisional results are given which show good estimates of the averaged response.
Improved periodic spectral analysis with application to diesel vibration data
Authors: Sherman Peter J. , White Lang B.
Published: October 2005

The purpose of this work is to begin the development of a comprehensive time/frequency spectral analysis approach that can be applied to complex signals associated with real world systems, such as rotating machinery. Rotating machinery operating at nominally constant speed comprise a large class of important real world systems that have received relatively little attention in terms of stochastic characterizations of any greater sophistication than those associated with wide sense stationary processes. In this work, a periodic-time/frequency characterization procedure is introduced in the context of vibration analysis associated with a diesel engine operating at nominally constant speed. This application highlights a number of difficulties, such as the need for accurate period estimation, accommodation of noninteger periods in relation to digital processing, and identification and separation of tonal components from the signature in order to arrive at a more parsimonious characterization. A theorem relating to the limiting influence of these difficulties is presented. These difficulties are addressed using advanced signal processing tools, such as a recently developed tone identification procedure and extended Kalman filtering, which to the authors’ knowledge have not been considered to date in such a setting. Results include a simple correction algorithm for noninteger periods, excellent separation of tonal components whose frequencies are slowly varying, and subsequently a modest improvement in the spectral characterization of the remainder of the process. These results have some significance in relation to diesel engine vibration, since they unambiguously identify tonal vibration components, in addition to a random structure which appears to include random excitation of resonances.
Finite-difference time-domain simulation of low-frequency room acoustic problems
Authors: Botteldooren D.
Published: October 2005

This paper illustrates the use of a numerical time-domain simulation based on the finite-difference time-domain (FDTD) approximation for studying low- and middle-frequency room acoustic problems. As a direct time-domain simulation, suitable for large modeling regions, the technique seems a good ‘‘brute force’’ approach for solving room acoustic problems. Some attention is paid in this paper to a few of the key problems involved in applying FDTD: frequency-dependent boundary conditions, non-Cartesian grids, and numerical error. Possible applications are illustrated with an example. An interesting approach lies in using the FDTD simulation to adapt a digital filter to represent the acoustical transfer function from source to observer, as accurately as possible. The approximate digital filter can be used for auralization experiments.
Acoustic and flexural wave scattering from a three-member junction
Authors: Rebinsky Douglas A. , Norris Andrew N.
Published: October 2005

A three-member junction is formed by a pair of semi-infinite plates in contact with fluid on one side and a mechanical structure on the other. The latter is described by an impedance matrix. The excitation is either a straight crested flexural wave traveling on one of the fluid-loaded plates and obliquely incident on the line junction, or an acoustic plane-wave incident from any direction in the fluid. The general solution for this type of scattering problem is derived and illustrative numerical examples are given. The admittance matrix for the fluid-loaded plate junction without the attachment plays a central role in the solution. It is verified that the general solution reduces to that for a pair of plates with clamped and welded junction conditions as limiting cases when the frame impedance is zero and infinite. The numerical results display two well-defined characteristic critical angles for transmission of structural energy and diffraction of acoustic pressure.
Experimental characterization of the vibrational behavior of a fluid-filled thin shell for the purpose of response estimation
Authors: Bai Mingsian R. , Lin Yiyan
Published: October 2005

Experimental techniques are proposed for developing a model to estimate structural vibrations induced by internal acoustic pressure at low frequencies. In these methods, the acoustic field and the structure are treated as a coupled system with the acoustic loading effect taken into account. The response model between the internal pressure and the surface vibration is established by a modified modal test on the coupled system. Experiments are performed to investigate the surface vibrations of a closed steel cylindrical shell excited by a loudspeaker inside. The experimental results show that developed techniques provide accurate estimation for the acoustically induced vibrations.
Sensitivity analysis for feedforward control system design
Authors: Rodríguez Héctor M. , Burdisso Ricardo A.
Published: October 2005

A sensitivity analysis for feedforward-controlled finite domain systems is presented. Using an analytical approach, the sensitivity of a controlled system to variations in the design variables of the control inputs and the error sensors is obtained. Since the physical implementation of the control inputs and the error sensors is directly related to the modal control forces and the modal error sensor components, the analysis is performed in the modal domain. This modal domain analysis offers the advantage that the highest computational effort in obtaining the sensitivities is independent of the physical characteristics of the transducers. From the results in the modal domain, the sensitivities of the controlled system with respect to particular physical parameters are obtained by using the chain rule of differentiation. Therefore, different types of transducers can be investigated within a minimum computational cost. The formulation can be easily incorporated into an optimization procedure for the optimal design of feedforward control systems. A numerical example in which the proposed formulation is compared to results obtained using finite differences is included.
Viscoelastic damping of particle and fiber reinforced composite materials
Authors: Dunn Martin L.
Published: October 2005

An analytical model is proposed for the analysis of viscoelastic damping in two-phase composite materials. The model is based on the coupling of the Mori–Tanaka [Acta Metall. 21, 571–574 (1973)] mean-field approach for the elastic behavior of composite materials with the viscoelastic correspondence principle to yield predictions for the complex viscoelastic moduli. Predictions are obtained for composites containing viscoelastic reinforcement that is either aligned, randomly oriented, or planar randomly oriented. Explicit expressions for the real and imaginary components of the effective moduli are presented for the technologically important case of an isotropic viscoelastic matrix containing elastic reinforcement. The analytical predictions for the complex bulk modulus of isotropic composites and the plane-strain bulk modulus of transversely isotropic composites are shown to lie on or within the bounds of Gibiansky and Milton [Proc. R. Soc. London Ser. A 440, 163–188 (1993)] for all reinforcement shapes and concentrations. Finally, a parametric study is carried out in the form of stiffness-loss maps for a wide range of composite microstructural geometries representative of technologically important material systems.
Phase singularities in scanning acoustical microscopy
Authors: Every A. G. , Hillmann K. , Würz K. U. , Hasselmann H. , Grill W.
Published: October 2005

Phase sensitive techniques in scanning acoustical microscopy (SAM) yield information on surface height, film thickness, and other sample attributes that is not easily obtained from amplitude imaging alone. The process of unwrapping to obtain the spatial dependence of the attribute from a phase image breaks down in the vicinity of singular points where the complex signal vanishes and the phase is indeterminate. In a circuit around a phase singularity the phase changes by 2π or −2π. This paper discusses a number of models which demonstrate how phase singularities can arise in SAM, and measured reflection and transmission SAM images containing phase singularities are presented.
Acoustic properties of selected bovine tissues in the frequency range 20–200 MHz
Authors: Akashi N. , Kushibiki J. , Chubachi N. , Dunn F.
Published: October 2005

The acoustic properties of freshly excised bovine liver, heart muscle, and fat are characterized in the frequency range 20–200 MHz by the bioultrasonic spectroscopy system using an ultrasonic transmission comparison method. Significant differences are obtained in the attenuation coefficient, velocity, impedance, and density among these tissues. Measurements of aqueous solutions of bovine hemoglobin are also reported in order to compare the contribution of the protein content to the acoustic properties. The differences among the acoustic properties of liver and heart muscle can be described in terms of their protein contents and other molecular constituents.
On a fractal packing approach for understanding ultrasonic backscattering from blood
Authors: Bascom Peter A. J. , Cobbold Richard S. C.
Published: October 2005

A new theoretical model is proposed to explain the change in the backscattered Doppler power with flow conditions. It defines a fractional packing dimension to represent the manner in which red blood cells are packed and this in turn is related to the variance of the scatterer number density. An explicit expression for the packing factor in terms of the integral of the pair correlation function is presented. Comparison of published experimental results for the backscattered power versus hematocrit with the theoretical model suggests that turbulence reduces the packing dimension. This reduction reflects a modification of the pair correlation function caused by changes in the flow field.
Mechanically coupled ears for directional hearing in the parasitoid fly Ormia ochracea
Authors: Miles R. N. , Robert D. , Hoy R. R.
Published: October 2005

An analysis is presented of the mechanical response to a sound field of the ears of the parasitoid fly Ormia ochracea. This animal shows a remarkable ability to detect the direction of an incident sound stimulus even though its acoustic sensory organs are in very close proximity to each other. This close proximity causes the arrival times of the sound pressures at the two ears to be less than 1 to 2 μs depending on the direction of propagation of the sound wave. The small differences in these two pressures must be processed by the animal in order to determine the incident direction of the sound. In this fly, the ears are so close together that they are actually joined by a cuticular structure which couples their motion mechanically and subsequently magnifies interaural differences. The use of a cuticular structure as a means to couple the ears to achieve directional sensitivity is novel and has not been reported in previous studies of directional hearing. An analytical model of the mechanical response of the ear to a sound stimulus is proposed which supports the claim that mechanical interaural coupling is the key to this animal’s ability to localize sound sources. Predicted results for sound fields having a range of incident directions are presented and are found to agree very well with measurements.
Shallow-water reverberation due to sediment volume inhomogeneities
Authors: Tang Dajun
Published: October 2005

This is a model of shallow-water reverberation due to sediment volume inhomogeneities. The scatterers are three-dimensional sound speed and density variabilities in the sediment. A first-order perturbation approximation is adopted assuming the sediment variabilities are small quantities. Within the applicable range of that approximation, this formalism is exact. It is found that the strength of the scattered field or reverberation strength can be expressed as the coupling between the incident and scattered normal modes. The mode coupling coefficient is found to be the same as the scattering coefficient sampled at relevant modal angles. In the development of the formulation, no empirical scattering function is involved. Also found is a dispersion factor associated with each mode in the mean reverberation curve corresponding to the spreading of the source pulse for each mode. Numerical examples are given for typical shallow-water environments.
Sound scattering at a rough water–sediment interface in shallow water
Authors: Tang X. , Tappert F. D.
Published: October 2005

The method of smoothing is used to study sound propagation and scattering in a realistic shallow-water environment with a randomly rough water–sediment interface. A mean field wave equation for the coherent acoustic field is obtained that has a complex-valued attenuation coefficient that is localized at the mean interface. The solution of the mean field equation, under highly idealized conditions, is derived and discussed. The branch point and pole singularities are found to be related to the head wave mode and the Biot–Tolstoy rough boundary wave mode, respectively. Also obtained is the coherent plane-wave reflection coefficient which is found to vanish when the acoustic frequency and the incident angle of the plane wave satisfy a certain resonant condition. For testing the mean field equation, a stochastic full-wave forward propagation PE model is developed for Monte Carlo simulations. The numerical results show that the coherent field obtained by an ensemble average over many realizations is in agreement with that obtained by solving the mean field equation just once. The Monte Carlo simulations also yield additional useful information about higher-order moments of the acoustic field. [Work supported by ONR.]
Benchmarks for backscatter in parabolic evolution
Authors: Smith Eric
Published: October 2005

Recently, a method was described for improving parabolic equations to account for intermediate backscattering induced by slow range dependence of the acoustic index of refraction. The method has found difficulty gaining acceptance, though, because there have been no readily available benchmarks for the systems to which it applies. This paper presents a method for constructing a class of benchmarks, by means of which a parabolic equation can be used to test itself for correct evolution through variations in sound speed. The method makes use of the conformal equivalence of changes in acoustic index of refraction to changes in geometry. As examples within this class, a set of special cases is treated analytically. These are exactly solvable models, in which intermediate backscattering leads to recognizable and physically significant effects. In particular, they can be used to show why energy conservation alone is not a sufficient requirement to produce correct parabolic evolution, even when it is physically appropriate. [Work supported by the ARL:UT Independent Research and Development Initiative.]
A unified perturbation approach to volume and roughness scattering
Authors: Ivakin Anatoliy N.
Published: October 2005

A unified approach is developed to study scattering from a fluid medium with irregularities of two different types: volume inhomogeneities (spatial fluctuations of the compressibility and density) and roughness of the interfaces. The approach treats roughness as a perturbation of the volume acoustic properties in the vicinity of the flat (unperturbed) surface. This permits a description of the scattering problem in terms of a unique integral equation for both types of irregularities. In the case of small roughness, the first iteration of this equation gives results corresponding to the extended Born approximation but provides a new approach for the case of interfaces with large, smooth roughness. As an application, acoustic scattering from a seabed consisting of an arbitrary number of irregular layers with volume inhomogeneities and rough interfaces is considered. [Work partially supported by ONR.]
Target strength of fluid-filled spherical shells related to material parameters and alternate filling fluids
Authors: Kaduchak Gregory , Loeffler Charles M.
Published: October 2005

Fluid-filled, thin spherical shells have been studied for use as passive sonar targets with applications in underwater navigation and calibration [see, e.g., D. L. Folds etal., J. Acoust. Soc. Am. 73, 1147–1151 (1983)]. The present research investigates the target strength of fluid-filled spheres as a function of shell and fluid parameters to aid in choosing alternative filling fluids. (Partial motivation is from the recent discontinuation of several chlorofluorocarbons which are commonly used.) Calculations based on 3-D elasticity theory describe the target strength dependence on the internal fluid density and sound speed. Here both time and frequency calculations of the form function and time domain scattering signatures describe favorable fluid characteristics. These features relate to the thickness and density of the confining spherical shell. It is shown that internal-fluid density requirements vary considerably for thin aluminum and stainless-steel shells. Several different filling fluids are tested in spherical shells with consideration given to effective target strength, safety considerations, and cost.
Sonolysis in liquid water without gas bubbles
Authors: Selivanovsky Dmitry A. , Domrachev Grigory A.
Published: October 2005

The present paper describes the results of measurements of hydrogen peroxide concentration in water under the action of relatively low-frequency sound without cavitation. Measurements of hydrogen peroxide concentration have been carried out with a high-sensitivity chemoluminescent method which has been elaborated for these experiments. De-ionized, degassed, high-purity water has been used. Acoustic resonators of a quarter of a sound wavelength were used as vertical columns made from high-purity quartz glass. Resonance frequencies were 1.2, 5.6, and 15 kHz. The pressure amplitude in the node at the hard bottom was smaller than 0.6 atm. The formation and accumulation of hydrogen peroxide were observed. For example, for the 20 °C water temperature and 1.2-kHz frequency the rate of increasing concentration rate is equal to 2×10−11 mol/(ℓ/h) for the degassed water and 8×10−10 mol/(ℓ/h) for a solution of magnesium sulfate in degassed water with a concentration similar to the one of the sea. The absence of gas bubbles was controlled by optical and acoustical methods. It is known that the appearance of hydrogen peroxide is a result of dissociation of a part of the water molecules. A hypothesis on the possibility of dissociation of water molecules at a small energy density due to acoustical and mechanical action is discussed.
Sound energy loss during sonolysis
Authors: Selivanovsky Dmitry A. , Domrachev Grigory A.
Published: October 2005

This paper gives an analysis of sound energy losses due to sonolysis — dissociation of the part of water molecules to radicals H⋅ and ⋅OH. The value of the energy loss can be evaluated by using the concentration of hydrogen peroxide which appears in the water as a result of cross-recombination of radicals ⋅OH+⋅OH=H2O2. Data previously obtained by different authors were used for the present analysis. Data for fresh water and also for water with dissolved gases were considered. Data covered a sound frequency range from 1.5 kHz to 2 MHz and sound pressure amplitudes 0.6–2.5 atm for normal static pressure and a water temperature of 20 °C. It is shown that the rate of increasing hydrogen peroxide concentration is proportional to the intensity of sound. The rate is also propor- tional to the concentration of dissolved oxygen and argon in water while other gases (hydrogen, helium, nitrogen) do not influence the sonolysis rate compared to the degassed water. All the data demonstrate that the energy loss is about proportional to the square of sound frequency, that is, the same frequency dependence with Rayleigh viscous attenuation of sound. The relative values of energy losses are from 10−4 to 10−8 of the Rayleigh sound decay. This value depends on the kind and concentration of dissolved gas in water.
Intelligibility of normal speakers: Error analysis
Authors: Neel Amy T.
Published: October 2005

Errors made by listeners in sentence transcription were analyzed to determine their contributions to intelligibility. One hundred Harvard sentences produced by ten males and ten females were transcribed by ten listeners per talker. Two measures of intelligibility were obtained: a keyword score in which a sentence was correct if, and only if, all five keywords were correct; and a total error count. Analysis of error types revealed that typing/spelling errors accounted for a third of total errors, and phonetic errors (consonant and vowel errors) accounted for another third. The remainder were semantic errors, added or deleted words, or unclassifiable. Further analysis of consonant errors did not reveal any particular type of consonant to be more susceptible to error than others. Male talkers had significantly worse keyword scores than females but did not have significantly greater total error counts indicating more errors on function words for females. The difference between high and low intelligibility speakers (by total error count) was accounted for by increased typing/spelling and consonant errors. Acoustic analysis of incorrectly transcribed words revealed that phonetic errors appeared to originate in the mouths of speakers while errors like word substitutions arise in the ears (or brains) of listeners.