bluuebunny/crossref_metadata_2025 huggingface dataset:
Elastic constants and structure of the vitreous system ZnO–P2O5
Authors: Higazy A. A. , Bridge B. , Hussein A. , Ewaida M. A.
Published: October 2005

The elastic moduli of the entire vitreous range of the system ZnO–P2O5 that can be prepared by melting ZnO and P2O5 oxides in open crucibles have been measured by ultrasonic techniques. The bulk, shear, longitudinal, and Young’s moduli, and the Poisson’s ratio are found to be rather sensitive to the glass composition. From these ultrasonic data, it is found that the glass system can be divided into ‘‘three compositional regions.’’ This behavior is qualitatively interpreted in terms of the zinc coordination, cross-link densities, and interatomic force constants.
Self-consistent perturbation approach to rough surface scattering in stratified elastic media
Authors: Kuperman W. A. , Schmidt Henrik
Published: October 2005

A unified, self-consistent perturbation approach to rough surface scattering in stratified media is presented. By introducing a boundary-condition operator formulation, the effect of the scattering on the mean field is accounted for by replacing the boundary conditions for the smooth interface with a set of effective boundary conditions involving relatively simple matrix operations. The formulation is valid for any type of interface between fluid or elastic layers, with the only change involved being the actual boundary operators. The use of boundary operator makes the formulation compatible with existing propagation models for stratified media, allowing simulation of scattering loss of the coherent component of the field due to the generation of a scattered field in the stratified fluid–solid media with an arbitrary number of rough interfaces. The scattered field, a by-product of the simulation is, in effect, the reverberation field in the stratified waveguide. The approach is verified by agreement with published theoretical results for specific interface types. Further, it is demonstrated qualitatively how rough surface scattering can account for some of the experimentally observed attenuation of seismic interface waves. Finally, the present approach is shown to agree with experimental results for an Arctic environment with a rough ice cover.
Wide-aperture reflection acoustics: Sonar experiments in shallow water
Authors: Carrion Philip M. , Wilbur JoEllen
Published: October 2005

In this paper, a simultaneous analysis of signals returned from the sea surface and the sea bottom in shallow water sonar experiments is discussed. The semblance function, which is a coherency measure of the recorded data corresponding to a pair of conjugate angles (conjugate angles are angles of equal magnitude with a common side that passes through the transducer and is parallel to the sea surface), was used. The semblance was analyzed as a function of grazing angle and frequency. It is shown that, for low grazing angles, sea-bottom and sea-surface reflections are highly coherent. The coherency breaks down for mid- and high-grazing angles. The analysis shows that the recorded signals are nonstationary. However, the amplitude characteristics of the returned signals behave as quasistationary over rather large time windows. The attenuation coefficient in marine sediments was evaluated from the measured data under the assumption of plane-wave propagation.
Experiments with violin plates and different boundary conditions
Authors: Jansson Erik V. , Niewczyk Benedykt
Published: October 2005

This paper reports on a continued investigation of violin plate properties. The plates were thinned in steps, and the shifts of the resonance frequencies were measured with different boundary conditions: free, glued to rigid ribs, and glued to the flexible ribs of a simplified violin model. It was found that, in spite of large frequency shifts for the free plates, the corresponding shifts for the glued plates were small. The experimental results imply that the boundary conditions have a major effect on the resonance frequencies and that the fundamental plate mode of the violin model is related to that of the free plate mode 5; i.e., the frequencies of both modes were most sensitive to thinning off-center and less sensitive to thinning in the center. The investigation is empirical; the information is collected under controlled conditions to serve as a base for future refined theoretical and experimental work.
Discrimination of rising and falling simulated single-formant frequency transitions: Practice and transition duration effects
Authors: Elliott Lois L. , Hammer Michael A. , Scholl Margo E. , Carrell Thomas D. , Wasowicz Jan M.
Published: October 2005

Two experiments evaluated discrimination of simulated single-formant frequency transitions. In the first experiment, listeners received practice with trial-by-trial feedback in discriminating either rising or falling frequency transitions of three different durations (30, 60, and 120 ms). Transitions either occurred in isolation or were followed by a steady-state sound matched in frequency to the transition end point. Some improvement in discrimination over practice runs occurred for the shortest transitions. Whether performance was evaluated at the beginning or end of practice, there were no differences attributable to transition direction or to whether transitions were followed by steady-state sound. Discrimination, however, was significantly better for the longest transitions. Just noticeable differences (jnd’s) for the longest transitions, measured in Hz at transition onsets, were of approximately the same magnitude as jnd’s for steady-state sounds that were equal in frequency to the midpoints of the transitions. Subjects of the second experiment discriminated the longer rising and falling transitions, but did not receive extensive practice. Results of experiment 2 replicated results of experiment 1 in showing similar jnd’s. Experiment 2 also showed no differences attributable to transition direction or to the presence of the steady-state sound following transitions.
Edge effects in short-pulse piezoelectric transducers
Authors: Hazony Dov
Published: October 2005

The electroelastic properties of thin-thickness-driven piezoelectric transducers are analyzed when the passive edges are free. The principal signals are relatively short stress pulses. It will be seen that these pulses travel close to or at the speed of sound in an unbounded medium and that, like in the one-dimensional space, circuit models, may be associated with these transducers. Special cases will be pointed out by examples.
Analysis of a radiating thin-shell sonar transducer using the finite-element method
Authors: Hamonic Bernard , Debus Jean Claude , Decarpigny Jean-Noël , Boucher Didier , Tocquet Bernard
Published: October 2005

The design of efficient low-frequency flextensional sonar transducers is a present challenge which is made difficult by a partial lack of general accurate mathematical models. Thus the application of the finite-element method to this problem is a promising approach which has been worked recently. To test the ability of the finite-element code atila [Decarpigny et al., J. Acoust. Soc. Am. 78, 1499–1507 (1985)] to predict the in-air and in-water dynamic behavior of such structures, an axisymmetrical thin-shell transducer was built, and its acoustical behavior was experimentally and numerically analyzed. This paper first presents the modal analysis of this projector, using different finite-element meshes as well as a mixed finite-element–plane-wave model and the comparison of numerical displacement field values to holographic measurements. Second, it describes an in-water harmonic analysis in which the model of the infinite fluid domain is reduced to a portion of the acoustic nearfield, limited by a spherical boundary upon which special damping finite elements are attached. All farfield quantities are then calculated using an efficient extrapolation algorithm [R. Bossut and J. N. Decarpigny, J. Acoust. Soc. Am. 86, 1234–1244 (1989)]. Finally, measured transmitting voltage response and directivity patterns are compared to the finite-element predicted values. The comparison proves the ability of the finite-element approach of provide detailed and accurate insights in the behavior of transducers working with shell vibrations.
Lateralization of bands of noise: Effects of bandwidth and differences of interaural time and phase
Authors: Trahiotis Constantine , Stern Richard M.
Published: October 2005

The effects of stimulus bandwidth on lateralization of narrow bands of noise were investigated with an acoustic pointing task. Stimuli were narrow bands of noise (centered on 500 Hz with bandwidths ranging from 50–400 Hz) that contained interaural time delays and/or interaural phase shifts. The overall extent of lateralization and sidedness was found to vary greatly as a function of stimulus bandwidth, as insightfully discussed earlier by Jeffress [L. A. Jeffress, Foundations of Modern Auditory Theory, edited by J. V. Tobias (Academic, New York, 1972)]. The data are qualitatively consistent with a weighted-image model [Stern et al., J. Acoust. Soc. Am. 84, 156–165 (1988)] that specifies and utilizes the shapes and locations of patterns of hypothesized neural activity. These patterns are topographically organized along a two-dimensional surface, and they describe the cross-correlation function of the stimuli as a joint function of frequency and the delay parameter of the cross-correlation operation. In this fashion, lateralization depends upon individual modes of such patterns that are weighed with respect to their straightness (consistency of interaural delay over frequency) and centrality (the extent to which interaural delays are small in magnitude).
Development of a structurally rigid, acoustically transparent plastic
Authors: Thompson Corley M.
Published: October 2005

Some underwater acoustical applications require a window that is both acoustically transparent and structurally rigid. No previous material possesses those properties, the closest being ‘‘PMP’’ plastic, whose specific acoustic impedance is 17% higher than seawater. A series of partially fluorinated epoxies is described that have sound speeds near water, but densities that are more than 50% higher than water. When these fluoroepoxies are compounded with glass microspheres to lower their densities, their sound speeds increase too much to permit a match to water. When they are compounded with a mixture of glass microspheres and phenolic plastic microspheres, they achieve both a sound speed and a density match to a water medium. A panel of such a composite had an insertion loss of less than 1 dB from 10 to 100 kHz at normal incidence. The composites have attractive engineering properties. The components are commercially available.
Theory of laminated piezoelectric plates for the design of distributed sensors/actuators. Part I: Governing equations and reciprocal relationships
Authors: Lee C. K.
Published: October 2005

A piezoelectric laminate theory that uses the piezoelectric phenomenon to effect distributed control and sensing of bending, torsion, shearing, shrinking, and stretching of a flexible plate has been developed. This newly developed theory is capable of modeling the electromechanical (actuating) and mechanoelectrical (sensing) behavior of a laminate. Emphasis is on the rigorous formulation of distributed piezoelectric sensors and actuators. The reciprocal relationship of the piezoelectric sensors and actuators is also unveiled. Generalized functions are introduced to disclose the physical concept of these piezoelectric sensors and actuators. It is found that the reciprocal relationship is a generic feature of all piezoelectric laminates.
Sound insulation characteristics of two-layered cylindrical shells partially exposed in a free field
Authors: Chonan S.
Published: October 2005

This paper is concerned with the sound insulation characteristics of two-layered cylindrical shells excited by a plane acoustic wave propagating axially within the shells. The shell has an infinite length; however, it is exposed in a free field by the length L. It is otherwise covered with rigid baffles. Each layer of the shell is assumed to bend according to a thick-shell theory, and the two sets of the shell equations are combined together through the continuity conditions of the displacements and tractions at the interface of the layers. The air surrounding the shell is described by the Helmholtz linear acoustic equation. The transmission loss through the shell wall, TL, is derived and calculated for various values of the physical parameters involved.
Modelization at oblique incidence of layered porous materials with impervious screens
Authors: Lauriks Walter , Cops André , Allard Jean F. , Depollier Claude , Rebillard Pascal
Published: October 2005

A matrix representation of the acoustical properties of porous layers at oblique incidence is used to predict the surface impedance of layered porous materials with impervious screens. The screens can be located inside the material or at the surface. Comparisons between prediction and measurement achieved with a new technique are given.
Auditory nonlinearities measured with auditory-evoked potentials
Authors: Chertoff Mark E. , Hecox Kurt E.
Published: October 2005

This article describes the use of auditory-evoked potentials (AEPs) as a tool to assess nonlinear processes in the auditory system. Two-tone signals were used as stimuli to obtain AEPs in both animal and human subjects. Frequency analysis of the physiologic waveforms revealed frequencies in the evoked potential that were not present in the acoustic signal. The largest distortion product in the evoked potential corresponded to the difference between the two primary frequencies (f2−f1). This distortion product was present in all subjects tested. Other distortion products at frequencies defined by n(f2−f1), where n<5, were also present in some individuals. These frequencies represent distortion components generated from an even-order nonlinear system. Extensive acoustic and electric calibration procedures provided substantial evidence that the distortion products recorded in the AEP were biologic in origin and not the result of acoustic or recording artifact.
Upward spread of masking, hearing loss, and speech recognition in young and elderly listeners
Authors: Klein Alan J. , Mills John H. , Adkins Warren Y.
Published: October 2005

Upward spreading of masking, measured in terms of absolute masked threshold, is greater in hearing-impaired listeners than in listeners with normal hearing. The purpose of this study was to make further observations on upward-masked thresholds and speech recognition in noise in elderly listeners. Two age groups were used: One group consisted of listeners who were more than 60 years old, and the second group consisted of listeners who were less than 36 years old. Both groups had listeners with normal hearing as well as listeners with mild to moderate sensorineural loss. The masking paradigm consisted of a continuous low-pass-filtered (1000-Hz) noise, which was mixed with the output of a self-tracking, sweep-frequency Bekesy audiometer. Thresholds were measured in quiet and with maskers at 70 and 90 dB SPL. The upward-masked thresholds were similar for young and elderly hearing-impaired listeners. A few elderly listeners had lower upward-masked thresholds compared with the young control group; however, their on-frequency masked thresholds were nearly identical to the control group. A significant correlation was found between upward-masked thresholds and the Speech Perception in Noise (SPIN) test in elderly listeners.
Ranging errors caused by angular misalignment between ultrasonic transducer pairs
Authors: Lamancusa John S. , Figueroa J. Fernando
Published: October 2005

Significant errors can occur in ultrasonic systems that measure the distance between separate transmitters and receivers when the transducers are not in angular alignment. This paper describes the results of experiments and numerical simulation to explain and quantify the ranging errors due to angular misalignment between ultrasonic transducer pairs. Two commercially available, 40-kHz piezoelectric transducer pairs are studied (10- and 25-mm diameter). The ranging error is shown to be a predictable function of the orientation angle.
The rotated parabolic equation and sloping ocean bottoms
Authors: Collins Michael D.
Published: October 2005

A new approach for solving problems involving sloping ocean bottoms with the parabolic equation (PE) method is presented. In most implementations of the PE, range-dependent environments have been approximated as a sequence of range-independent regions. The PE, which has one range derivative, does not conserve both pressure and the normal component of particle velocity across boundaries between regions. For problems involving sloping ocean bottoms, this can lead to large errors for slopes of only a few degrees. The rotated PE, which marches parallel to the ocean bottom and has two normal derivatives, handles sloping interfaces properly. A benchmark solution for an upslope problem is presented to demonstrate the accuracy of the rotated PE.
Modeled time variability of acoustic propagation through a Gulf Stream meander and eddies
Authors: Mellberg Leonard E. , Robinson Allan R. , Botseas George
Published: October 2005

A numerical modeling study of the time variability of acoustic propagation through a Gulf Stream meander and eddies is presented. Both a cold-core (cyclonic) eddy and a warm-core (anticyclonic) eddy are included. Time periods of 2, 4, and 7 days; a frequency of 25 Hz; source and receiver depths of 150 m; and propagation out to 180 km are considered. Propagation conditions assumed an absorbing bottom and no azimuthal coupling of energy. Results indicate that variations in the locations and propagation loss levels of convergence zones (CZ) in 2 days can be significant. In the first CZ, the losses can change by more than 5 dB and shift in their pattern range location by as much as 10 km. Changes in the environment over a 2-day period can be such that perturbations to the acoustic field caused by the environment within the first CZ can be nullified by the environment between the first and second CZs. The differences between propagation with the eddies present and not present were also observed for ranges out to the first CZ. For a source located in the center of a cold-core eddy, the propagation loss in the CZ increased by 3 dB and the range decreased by about 5 km. With the source located within the eddy but off center, the loss showed little change in level but the range again decreased by about 5 km. For a source located in the center of a warm eddy, the propagation loss in the CZ increased by about 3 dB and the range increased by 7–10 km. With the source located off center, the loss showed little change in level and range location.
Comments on the calculation of cross sections for elastic-wave scattering using the T matrix
Authors: Lim Raymond , Hackman Roger H.
Published: October 2005

The basic formulas for the calculation of cross sections for elastic-wave scattering from elastic and viscoelastic bodies are reviewed from a simpler perspective than normally encountered, with an emphasis toward casting them into a form suitable for calculation with the T-matrix formalism. The original formulas of Gubernatis et al. [J. E. Gubernatis, E. Domany, and J. A. Krumhansl, J. Appl. Phys. 48, 2804–2811 (1977); J. E. Gubernatis, E. Domany, J. A. Krumhansl, and M. Huberman, J. Appl. Phys. 48, 2812–2819 (1977)] are obtained and the asymmetric dependence of their optical theorem on the mode of the incident plane-wave field is resolved by incorporating an average over a phase error. Corrected forms for the T matrix in scattering from a single sphere in an elastic medium are presented.
Sharpness and amplitude envelopes of broadband noise
Authors: Ueda Kazuo , Akagi Masato
Published: October 2005

This paper discusses how amplitude envelope shapes, sound-pressure level, and duration of broadband noise affect sharpness and brightness. In the first experiment, sharpness, brightness, and similarity were judged for paired stimuli by 13 subjects. The stimuli consisted of broadband noise with different types of amplitude envelopes, sound-pressure levels, and duration. Experimental results were analyzed with a multidimensional scaling technique. In addition, the second experiment measuring the point of subjective equality (PSE) of sharpness was carried out for four subjects. The results of these two experiments showed large individual differences in sharpness judgment, difficulty in brightness judgment for the stimuli used in the experiments, and influence of the amplitude envelope shapes on sharpness. The individual differences observed in sharpness judgment were explained by the differences between weights given to two psychological dimensions: loudness and subjective duration. This study forms a basis for understanding sharpness of nonsteady sounds.
Evaluation of a spectrum target prediction model in speech perception
Authors: Akagi Masato
Published: October 2005

A model of a spectrum target prediction mechanism is proposed and evaluated by comparing predicted values with results of psychoacoustic experiments. When the trajectory of the cepstrally smoothed LPC spectrum is approximated by a second-order critically damped system, the proposed model can estimate target values using short-period spectrum sequences (50 ms) without being given the onset positions of the spectral transition. Additionally, this model decreases the length of transitional sounds and recovers vowel characteristics neutralized by coarticulation. Moreover, this model compensates for the transitions of syllables and extracts stable characteristics from syllable transitions. This model is applicable to coarticulation recovery in speech signal processing.
Acoustic pulse propagation above grassland and snow: Comparison of theoretical and experimental waveforms
Authors: Albert Donald G. , Orcutt John A.
Published: October 2005

Theoretical predictions are made of the effect of an absorbing ground surface on acoustic impulsive waveforms propagating in a homogeneous atmosphere for frequencies below 500 Hz. The lower frequencies of the pulse are enhanced as the effective flow resistivity of the ground surface decreases and as the propagation distance increases. The pulse waveforms and peak amplitude decay observed for propagation distances of 40 to 274 m over grassland were satisfactorily matched by calculations using an assumed effective flow resistivity of 200 kN s m−4. Measurements over snow gave much greater amplitude decay rates, and the waveforms were radically changed in appearance, being dominated by the lower frequencies. These waveforms were satisfactorily matched only when a layered ground was incorporated into the calculations; then, an assumed surface effective flow resistivity of 20 kN s m−4 gave good agreement with the observed waveforms and peak amplitude decay.
Scholte wave characterization and its decay for various materials
Authors: Nasr Salah , Duclos Jean , Leduc Michel
Published: October 2005

The Scholte wave propagating at a liquid/solid interface is studied. A device associating an interdigital transducer and a thin piezoelectric film generates such a wave on dielectric substrates; appropriate sticking allows propagation on conducting mediums. The location of the Scholte wave was experimentally checked, its velocity was measured, its weak attenuation was verified, how it decays was widely examined in the liquid medium perpendicular to the interface.
Acoustic radiation pressure on a rigid cylinder: An analytical theory and experiments
Authors: Wu Junru , Du Gonghuan , Work Steven S. , Warshaw David M.
Published: October 2005

Simple and general analytical expressions are derived for the acoustic radiation force on a long rigid cylinder with a small diameter, whose axis is perpendicular to the wave propagation. Results are expressed in terms of the time-averaged densities of kinetic and potential energies of the incident sound field. For the case of a standing-wave field, which was used in these experiments, the theoretical results agree well with the experimental observations.
Seasonal sonar observations of the diurnal shoaling times of fish
Authors: Weston David E. , Andrews H. W.
Published: October 2005

Long-range sonar observations over a number of years have shown tracks due to shoals of fish, which usually disappear near dusk and reappear near dawn. Five types of behavior may be distinguished: (1) Commonly, the boundary between the day and night patterns is spread over a large part of an hour; (2) in the late summer, the changeover sometimes lasts only a few minutes, due to a change in the attenuation; (3) again, in the late summer, light bands may appear on the records near dusk and dawn for the order of an hour, due to low reverberation levels accompanying a high attenuation; (4) sometimes the shoals break up by a process akin to diffusion, which is seen to produce fanlike patterns; (5) although most shoals break up at night, about half the records still show a few shoal tracks. The timings have been estimated for the years 1963–1968. The disappearances tend to occur close to civil twilight, although they are a little earlier in the summer. The appearances tend to occur close to sunrise, but are a little later in the summer.
A cochlear frequency-position function for several species—29 years later
Authors: Greenwood Donald D.
Published: October 2005

Accurate cochlear frequency-position functions based on physiological data would facilitate the interpretation of physiological and psychoacoustic data within and across species. Such functions might aid in developing cochlear models, and cochlear coordinates could provide potentially useful spectral transforms of speech and other acoustic signals. In 1961, an almost-exponential function was developed (Greenwood, 1961b, 1974) by integrating an exponential function fitted to a subset of frequency resolution-integration estimates (critical bandwidths). The resulting frequency-position function was found to fit cochlear observations on human cadaver ears quite well and, with changes of constants, those on elephant, cow, guinea pig, rat, mouse, and chicken (Békésy, 1960), as well as in vivo (behavioral–anatomical) data on cats (Schucknecht, 1953). Since 1961, new mechanical and other physiological data have appeared on the human, cat, guinea pig, chinchilla, monkey, and gerbil. It is shown here that the newer extended data on human cadaver ears and from living animal preparations are quite well fit by the same basic function. The function essentially requires only empirical adjustment of a single parameter to set an upper frequency limit, while a ‘‘slope’’ parameter can be left constant if cochlear partition length is normalized to 1 or scaled if distance is specified in physical units. Constancy of slope and form in dead and living ears and across species increases the probability that the function fitting human cadaver data may apply as well to the living human ear. This prospect increases the function’s value in plotting auditory data and in modeling concerned with speech and other bioacoustic signals, since it fits the available physiological data well and, consequently (if those data are correct), remains independent of, and an appropriate means to examine, psychoacoustic data and assumptions.
Level discrimination of frozen and random noise
Authors: Buus So/ren
Published: October 2005

This paper examines how the difference limen for level, ΔL, is affected by stimulus bandwidth and variability. The ΔL’s were measured in three normal listeners using an adaptive two-interval, forced-choice procedure. The 30-ms stimuli were a 3-kHz tone and nine noise bands with half-power bandwidths ranging from 50 Hz–12 kHz. Except for the 12-kHz bandwidth, which was a low-pass noise, the noise bands were centered at 3 kHz. The ΔL’s were measured for both frozen and random noises presented at 30, 60, or 90 dB SPL overall. For frozen noises, the same sample of noise was presented throughout a block of 50 trials; for the random noises, different samples of noise were used in each interval of the trials. Results show that the ΔL’s are higher for random than for frozen noises at narrow bandwidths, but not at wide bandwidths. The ΔL’s for frozen narrow-band noises decrease with increasing level and are similar to those for the pure tone, whereas the ΔL’s for wideband noises are only slightly smaller at 90 than at 30 dB SPL. An unexpected finding is that the ΔL’s are larger at 60 than at 30 dB SPL for both frozen and random noises with bandwidths greater than one critical band. The effect of bandwidth varies with level: The ΔL’s decrease with increasing bandwidth at low levels, but are nearly independent of bandwidth at 90 dB SPL. The interaction of bandwidth and level is consistent with the multiband excitation-pattern model [M. Florentine and S. Buus, J. Acoust. Soc. Am. 70, 1646–1654 (1981)], but the nonmonotonic behavior of ΔL as a function of level suggests modifications to the model.
Sonar pulse radiation and filtering in the mustached bat, P
t
e
r
o
n
o
t
u
s p
a
r
n
e
l
l
i
i r
u
b
i
g
i
n
o
s
u
s
Authors: Hartley David J. , Suthers Roderick A.
Published: October 2005

Parnell’s mustached bat, Pteronotus parnellii, uses echolocation to hunt for insects in the New World tropics. The sonar signals, which are emitted from the mouth, are long, constant-frequency types with a ‘‘missing’’ fundamental, so that the second and third harmonics contain most of the pulse energy. This pulse structure implies that the supraglottal vocal tract acts as an acoustic notch filter for the fundamental. To investigate this possibility, light and heavy gases were used to obtain the vocal tract transfer function. The results show that a fundamental notch filter is present, and anatomical manipulations of the vocal tract suggest that this filtering is achieved by a combination of antiphasic reflections from the nasal passages and an area-function filter in the throat. During these experiments, tracheal sound was also monitored to assess the acoustical role of the tracheal sac. This is an elastic section of the trachea, situated immediately posterior to the larynx, which inflates during vocalization. While demonstrating that this structure plays a significant role in determining the acoustics of the subglottal system, our results neither confirm nor dismiss the hypothesis that it reflects sound back to the larynx to improve vocal efficiency. As part of the investigation, the radiation pattern for the mustached bat was also obtained and was compared with various model sources. At the second and third harmonics, sound radiation is highly directional and consistent with the idea that the mouth acts as a conical horn.
Comments on ultrasonic propagation in suspensions
Authors: Ma Yushieh , Varadan Vijay K. , Varadan Vasundara V.
Published: October 2005

In determining the velocity and attenuation of suspensions of spherical particles, results obtained from the computationally simpler multiple scattering approach of Waterman and Truell (WTF) and from a multiple scattering formalism (MSF), which considers the pair correlation function, have been compared in order to justify the range and applicability of the former method. Although the difference between the results increases as the concentration of suspensions increases, the frequency-dependent attenuation computed from the two approaches can be quite different particularly in the low-frequency range even at lower concentrations. Due to the unavailability of experimental data for ultrasonic propagation, data from analogous optical experiments on suspensions of latex spheres are compared. The MSF shows excellent agreement, whereas the WTF shows large discrepancies from the experimental data.
Time–frequency analysis of acoustic scattering from elastic objects
Authors: Yen Nai-chyuan , Dragonette Louis R. , Numrich Susan K.
Published: October 2005

Some characteristics of an insonified object are generally present in the signal carried by the returning scattering wave. As an echo is the result of the wave interaction with a material structure, such a response is distinctive for a body of given shape and composition. Traditionally, to express the information content in the echo signature, either the frequency response (transfer/form function) or the time signature (impulse response) is employed; however, for a detailed study of the scatterer’s structure, a joint time and frequency analysis is performed. The aim of this analysis is to develop a simple processing algorithm for extracting the prominent features, which can then be used to determine the physical parameters of the object. The approach is based on the modified version of the Wigner distribution function (WDF) and utilizes an image-processing technique to depict the outstanding highlights of the scatterer’s response in a two-dimensional time and frequency display. The physical parameters of the scatterer are then extracted from this diagram with the proper interpretation and understanding of the scattering phenomena. Several examples, based on data obtained from numerically simulated models and laboratory measurements for elastic spheres and shells, are used to illustrate the capability and proficiency of the algorithm. Separable traces in time-frequency space are related to the specular reflection, creeping waves, and various reradiated elastic modes. From these, the general physical size, the corresponding wave speeds (elastic properties), and the density of the insonified object can be estimated.
Measurements of acoustic wave velocities and attenuation in marine sediments
Authors: Turgut Altan , Yamamoto Tokuo
Published: October 2005

Propagation and attenuation of acoustic waves in fluid-saturated sediments have been studied theoretically and experimentally. In situ acoustic transmission tests in saturated beach sand show that compressional waves are dispersive within a certain frequency band where the intrinsic attenuation is maximum. This indicates that low-frequency wave velocities in marine sediments are at least 5% to 10% less than the velocities obtained from high-frequency measurements, and viscous damping, due to the relative motion between solid skeleton and fluid, is the main damping mechanism in the frequency range of 1–30 kHz. The agreement between the experimental results and Biot’s theory enables the remote determination of porosity and permeability of marine sediments by using measured compressional and shear wave characteristics. Approximate relations are used to determine the porosity and permeability of the marine sediments using the measured acoustic wave velocities and attenuation.
Calculation of turbulence effects in an upward-refracting atmosphere
Authors: Gilbert Kenneth E. , Raspet Richard , Di Xiao
Published: October 2005

The parabolic equation (PE) method is used together with a two-dimensional atmospheric turbulence model to calculate the effect of turbulence on sound propagation. Both a nonrefractive atmosphere and a refractive atmosphere are considered. The nonrefractive calculation serves as a test of the two-dimensional model for turbulence. For a nonrefractive atmosphere, good agreement is obtained with experiment and the theory of Daigle. The calculation with upward refraction is compared to the data of Weiner and Keast who observed that the relative sound-pressure level versus range follows a characteristic ‘‘step’’ function. The calculations, which contain no adjustable parameters, give reasonable agreement with the data. In particular, the shape of the step function is well predicted. In the geometric shadow region, the observed strong dependence on refraction strength and weak dependence on range, height, and frequency are also predicted. It is concluded that, for a receiver deep in a shadow zone and frequencies greater than a few hundred hertz, the measured sound-pressure level is due almost entirely to sound scattered into the shadow zone by atmospheric turbulence. Consequently, for upward refraction and frequencies above a few hundred hertz, turbulence must be included in long-range propagation calculations if one is to obtain useful predictions.
Bubblelike scatterer monolayers at solid–fluid interfaces: Effects on reflectivity
Authors: Tolstoy I.
Published: October 2005

Air-filled bubbles and bubblelike scatterers (balloons, very thin shells, and cavities in rubberlike layers) of radius a, in a liquid of sound velocity c, satisfy the compactness condition ka<1 at frequencies ω=kc in the neighborhood of their resonant ‘‘bubble’’ frequency ω0. One can therefore describe the scatter from a monolayer of such scatterers at an interface between two media using the generalized smoothed-boundary theory developed by this writer elsewhere [I. Tolstoy, J. Acoust. Soc. Am. 75, 1–22 (1984); 79, 666–672 (1986)] in which the scatterers are replaced by distributions of monopoles and dipoles. For bubblelike scatterers, and for ω≂ω0, the monopole contributions outweigh the dipole contributions by many orders of magnitude; there is then a layer of monopoles whose effective scattering cross sections near resonance are between 1012 (bubbles in water) and 106 (cavities in rubber) times that of a small hard sphere of the same radius. Such monolayers lead to major changes of reflectivity—which can be calculated rather simply, using plane distributions of scatterers, e.g., a square lattice of basis l on a hard wall, with or without taking into account monopole interaction through multiple scatter.

In either case, the models predict the existence of kl values at which the wall/fluid interface becomes anechoic at or close to ω=ω0. Numerical examples are given for air-filled cavities in rubberlike materials next to a perfectly hard wall. In practice, anechoic conditions are approximated for a narrow band of frequencies ωA±Δω, ωA≂ω0, and Δω/ωA≂10−2 for soft rubber (FJ95) and ≂5×10−2 for harder rubbers [FJ65: using constants given by Gaunaurd et al., J. Acoust. Soc. Am. 65, 573–594 (1979)]. For given ωA, the effect is, in practice, less sensitive to spacing kl (departures of ±25% from the exact value are tolerable). Simple theoretical considerations suggest that similar anechoic conditions will be achieved for elastic plates with the same cavity distributions in an interfacial rubber layer. A constant ambient pressure is implicitly assumed throughout (horizontal interfaces and monolayers).
Level crossing probabilities for multipath acoustic processes with bimodal spectra
Authors: Perakis Anastassios N. , Lyridis Dimitrios V.
Published: October 2005

A general method of evaluating upcrossing probabilities for a class of random processes consisting of two narrow-band signals is presented. One of the two significant frequencies of the corresponding bimodal spectra is assumed to be dominant. The method approximates the maxima of these processes by the corresponding values of the envelope processes. It is also assumed that the discrete processes of the maxima are Markov. The results have several applications. Two prominent examples are detection problems of multipath partially saturated processes in underwater acoustics and the problem of the structural reliability of marine diesel engine shafting systems.
Optimum bearing resolution for a moving towed array and extension of its physical aperture
Authors: Stergiopoulos Stergios
Published: October 2005

This paper examines the limits of the angular resolution capability of a moving towed array (MTA) by finding the Cramer–Rao lower bounds (CRLB) and provides algorithms that extend the physical aperture of an MTA. The model that is considered for the CRLB estimates assumes that an N-hydrophone towed array is moving at a known constant speed and that in the received signal unknowns are all the parameters for two sources. The estimated CRLBs for this model indicated that an N-hydrophone MTA provides very high angular resolution when the duration T of the received signal is very long. This ability of the moving array to resolve two closely spaced sources is related to the fact that the physical aperture has been extended by the distance traveled by the array during the T seconds of the observation period. Computer-simulation examples using a maximum-likelihood estimator and an extended towed array algorithm to find the bearing of sources are presented. The results of these simulations agree with the CRLB if the signal-to-noise ratio (SNR) is higher than 0 dB at the hydrophone level, which suggests that both of the above techniques are efficient estimators. Real-data applications using the extended towed-array algorithm were successful, and the physical aperture of a 32-hydrophone MTA was extended to an equivalent of a 512-hydrophone fully populated array during 185 s of observation period. These results have also indicated that the performance of the above algorithm is very robust, since it extends the physical aperture of an array by more than one order of magnitude for the case of a very low signal-to-noise ratio (SNR) broadband signal and for a pure tone, even though the source had a speed of 3.6 kn along its bearing.
A multiple-frequency hydrophone calibration technique
Authors: Smith Robert A. , Bacon David R.
Published: October 2005

A method is described for comparing the sensitivity of two hydrophones over the frequency range 1–15 MHz. This technique forms the basis for the dissemination of national ultrasonic standards in the U.K. over this frequency range. A reference hydrophone is placed in an ultrasonic field and then the device being calibrated is substituted and the two output voltages are compared. This substitution method utilizes a broadband ultrasonic field produced by nonlinear propagation. Thus it is possible to cover the whole frequency range with a single measurement on each hydrophone. The overall uncertainty in the intercomparison of two hydrophones increases from ±4.2% at 1 MHz to ±8.2% at 15 MHz (95% confidence level). The method has been compared with discrete-frequency substitution, time-delay spectrometry, and absolute calibrations using the National Physical Laboratory (NPL) primary standard laser interferometer. Various designs and sizes of hydrophones were compared, and agreement was within the combined random uncertainties for all the comparisons.
Comparison of effective medium and multiple-scattering theories of predicting the ultrasonic properties of dispersions
Authors: McClements D. J. , Fairley P. , Povey M. J. W.
Published: October 2005

Analytical expressions of the effective density and compressibility of a scattering medium derived using multiple-scattering theory (MST) and effective medium theory (EMT), assuming no R dependence, are compared. The EMT and MST are shown to be equivalent in the long wavelength limit. Differences between the ultrasonic velocity and attenuation predicted by the two theories, observed by earlier workers, can be attributed to the fact that simplified expressions for the scattering coefficient An were used in the EMT.
Density–sound velocity relationships for two marine surface sediment classes
Authors: Rayborn Grayson H. , Ioup Juliette W. , Ioup George E.
Published: October 2005

The density to sound velocity dependence of two predominant classes of continental shelf surface sediments [E. L. Hamilton, J. Acoust. Soc. Am. 68, 1313–1340 (1980)] can be described as a subclass of Nobes’ cases [J. Acoust. Soc. Am. 86, 290–294 (1989)] by the Wood equation [A. B. Wood, A Textbook of Sound (Macmillan, New York, 1941)] or by straight line fits to the Wood equation or the data [Rayborn et al., J. Acoust. Soc. Am. Suppl. 1 80, S113 (1986)]. The results can be used to calculate the surface sediment densities from sound speed measurements and to get estimates of the average grain densities and velocities of the sediments, as well as in choosing model study parameters.
On the invention of active noise control by Paul Lueg
Authors: Guicking D.
Published: October 2005

A historical report is given on the invention of active noise control which is related to the person of Paul Lueg, a doctor of philosophy and medicine, who worked as a physicist for many years. He submitted, early in 1933, a patent application describing for the first time the principle of active noise cancellation. Long before any technical realization, he had recognized the essential aspects of this method. It was his personal tragedy that he ran, by this patent, into severe controversies with Nazi army authorities. Instead of recognition (and profit), the invention brought him nothing but detriments which overshadowed his further life.
Parameter interpolation in speech synthesis
Authors: Wright R. D. , Elliott S. J.
Published: October 2005

A comparison has been made of the transition properties of six types of speech synthesizer parameters: serial resonance, prediction coefficients, reflection coefficients, area functions, parallel resonance, and, finally, a simple set of articulatory parameters. The first four synthesizers are formally equivalent and can be made to produce identical steady-state sounds (targets). The last two involve approximations, but achieve similar targets. Formant paths between targets will differ according to the parameter type used during interpolation. Each type was tested on nonsense words spanning a wide range of parameter values. Linear interpolation of synthesizer parameters was used to determine a path between target values. The resultant data were then converted to formant values and plotted as a spectrographic (frequency versus time) representation. Small differences in formant frequency (versus linear transitions of formant frequency and bandwidth) were common, and some quite large differences in formant bandwidths were observed in certain cases.
The speed of a tube wave
Authors: Norris A. N.
Published: October 2005

The low-frequency tube wave speed is given explicitly for a variety of borehole environments. The presence of a logging tool, the effects of casing, and bore eccentricity are considered. The results are all relatively simple and indicate that the speed decreases in the presence of a tool or borehole eccentricity. The speed increases in the presence of casing as long as the casing shear modulus exceeds that of the formation.
Target strengths of Antarctic krill (E
u
p
h
a
u
s
i
a s
u
p
e
r
b
a) at 38 and 120 kHz
Authors: Foote Kenneth G. , Everson Inigo , Watkins Jonathan L. , Bone Douglas G.
Published: October 2005

Encaged aggregations of live krill in good to pristine condition have been ensonified at 38 and 120 kHz. Concurrent underwater television observations of behavior resemble those made by underwater divers in naturally occurring swarms, with comparably high densities of the order of 104 animals/m3 . Mean, single-animal target strengths have been inferred from measurements of echo energy. For aggregations with mean lengths in the range [30,39] mm, the mean single-krill target strengths are in the range [−88,−83] dB at 38 kHz and [−81,−74] dB at 120 kHz. Collateral measurements on some of the same encaged specimens determined a density contrast of 1.0357±0.0067 and sound-speed contrast of 1.0279±0.0024, relative to seawater. These numbers have been used with the fluid-sphere model as stated by Greenlaw [Limnol. Oceanogr. 24, 226–242 (1979)] . Computed backscattering cross sections have been averaged over the length distributions of each measured aggregation, resulting in target strength predictions in the range [−86,−80] dB at 38 kHz and [−79,−76] dB at 120 kHz.