bluuebunny/crossref_metadata_2025 huggingface dataset:
Numerical study on the acoustic field of a fluid-filled borehole in an elastic medium
Authors: Zhang H. L. , Li M. X.
Published: October 2005

The space distribution of the whole field at successive instants of time inside and outside a fluid-filled borehole in an elastic medium radiated by an acoustic source on the axis of the borehole is numerically calculated. The results reveal the structure of the field and show that the field is formed mainly by two mechanisms, the interaction of the acoustic wave with the borehole boundary and the interference among all wave components.
Dynamic analysis of finite, three-dimensional, linear, elastic solids with Kelvin viscoelastic inclusions: Theory with applications to asymmetrically damped circular plates
Authors: Shen I. Y. , Mote C. D.
Published: October 2005

Eigensolutions and Green’s functions of finite, three-dimensional, linear, elastic solids with Kelvin viscoelastic inclusions are analyzed. The eigensolutions satisfy a set of integral equations expressing the reciprocal theorem of viscoelasticity. Successive approximations to these integral equations lead to asymptotic solutions and an iteration scheme for the eigensolutions. The Green’s function is also determined through the integral equation approach. Finally, the vibration of Kirchhoff circular plates with evenly spaced, radial, viscoelastic inclusions, which cause some of the repeated vibration modes to split into distinct ones, is analyzed both analytically and numerically for the eigensolutions and the Green’s function.
Temperature dependences of the acoustic nonlinearity parameter B/A of aqueous solutions of amino acids
Authors: Chalikian T. V. , Sarvazyan A. P. , Funck Th. , Belonenko V. N. , Dunn F.
Published: October 2005

A differential technique for evaluating the molar increments of the nonlinearity parameter B/A has been employed for investigations of aqueous solutions of the amino acids glycine, alanine, norvaline, norleucine, arginine monohydrochloride, and lysine monohydrochloride in the temperature range 18 °C–45 °C. Some regularities of temperature dependencies of the nonlinearity parameter B/A of hydration shells of charged and aliphatic groups have been found. Contributions of these groups to the value of B/A molar increments of solute versus temperature have been estimated.
Signal detection in temporally modulated and spectrally shaped maskers
Authors: van den Brink Willem A. C. , Houtgast Tammo , Smoorenburg Guido F.
Published: October 2005

The first part of this paper presents several experiments on signal detection in temporally modulated noise, yielding a general approach toward the concept of comodulation masking release (CMR). Measurements were made on masked thresholds of both long- and short-duration, narrow-band signals presented in a 100% sinusoidally amplitude-modulated (SAM) noise masker (modulation frequency 32 Hz), as a function of masker bandwidth from 1/3 oct up to 13/3 octs, while the masker band was geometrically centered at signal frequency. With the short-duration signals placed in the valley of the masker, a substantial CMR (i.e., a decrease of masked threshold with increasing masker bandwidth) was found, whereas for the long-duration signals CMR was smaller. Furthermore, investigations were carried out to determine whether CMR changes when the bandwidth of the signals, consisting of bandpass impulse responses, is increased. The data indicate that substantial CMR remains even when all masker bands contain a signal component, thus minimizing across-channel differences. This finding is not in line with current models accounting for the CMR phenomenon. The second part of this paper concerns signal detection in spectrally shaped noise. Also investigated was whether release from masking occurs for the detection of a pure-tone signal at a valley or a peak of a simultaneously presented masking noise with a sinusoidally rippled power spectrum, when this masker was preceded and followed by a second noise (temporal flanking burst) with an identical spectral shape as the on-signal noise. Similar to CMR effects for temporal modulations, the data indicate that coshaping masking release (CSMR) occurs when the signal is placed in a valley of the spectral envelope of the masker, whereas no release from masking is found when the signal is placed at a peak of the spectral envelope of the masker. The implications of these experiments for measures of spectral and temporal resolution are discussed.
Stop consonant identification using auditory images.
Authors: Feth Lawrence , Fox Robert Allen , Bicknell Ina
Published: October 2005

A number of researchers over the past decade have argued that salient characteristics of auditory processing must be incorporated into speech recognition models before they can accurately represent human speech processing which might, in turn, improve recognition accuracy. Recently, Fox and Feth [Proc. Ninth International Symposium on Hearing, Carcans, France (1991)] processed a series of stop+vowel CVs (using [bdgptk] and the vowels [i schwa æ open aye u]) through Patterson and Holdsworth’s auditory sensation processing (ASP) model producing a set of ‘‘stabilized auditory images.’’ Each image represented a spectral representation of 15 ms of the acoustic signal and the images for each token could be displayed in rapid sequential order producing a ‘‘cartoon’’ of the auditory changes evident over a wide range of auditory analysis channels. A set of viewing experiments conducted using three subjects demonstrated that these stops (and vowels) could be accurately identified on the basis of the dynamic auditory cues contained in the auditory images. Accuracy rates up to 99% for voicing and 92% for place of articulation were obtained. The present study is a continuation of this research using a longer display window that may more accurately reflect short auditory memory in perceptual processing. [Research supported, in part, by an AFOSR grant to L. Feth and a NIA grant to R. Fox.]
A model of jet-resonator action based on the air reed, or vibrating diaphragm, concept.
Authors: Elder S. A.
Published: October 2005

Both cavity resonance, or ‘‘half-jet’’ drive, and organ pipe, or ‘‘full-jet’’ drive, can be described in terms of a model based on an extension of the ‘‘air reed’’ concept of Yoshikawa and Soneyoshi [J. Acoust. Soc. Jpn. (E) 1, 175–191 (1980)]. For the half-jet, or free shear layer, the effective vibrating diaphragm is the moving surface defined by the locus of points at which the shear layer velocity profile has an inflection point. Since this is the layer that separates ‘‘outside’’ from ‘‘inside’’ fluid in the shear layer, its behavior at the downstream edge determines how much external fluid is available for each cycle to drive the acoustic resonance of the cavity, considered as a parallel-resonant system (i.e., ‘‘jet drive’’ in control-volume type models). For the organ pipe case, the back-to-back shear layers of the full jet provide a pair of coupled ‘‘diaphragms’’ which act similarly. In addition to parallel-resonant action, the transverse material acceleration of the jet motion can be associated with series resonant, or ‘‘force-drive’’ contributions to the oscillation that arise principally from fluctuating deflection of momentum from the main jet flow. Insights from current studies on underwater half-jet resonators will be described. [Work supported by U.S. Naval Academy Research Council.]
Hearing based analysis of engine noise.
Authors: Fritz Gerold
Published: October 2005

Sounds, produced by different car engines were examined with various analysis techniques. Additionally, a group of randomly chosen tests subjects estimated the loudness impression of different sounds. These studies showed, that time function, FFT spectrum, and third-octave spectrum provide no sufficient signal characterization. Different types of car engines, like diesel or otto cycle engines sound different, even though they may have the same spectra. As an alternative a psychoacoustic method is presented, which calculates the impulse content of sound, based on the spectrum of specific loudness. These loudness spectra are calculated according to the ‘‘Zwicker standard’’ directly from the signal in the time domain. The calculated results correlate with the statements of the test subjects very well.
Temporal modulation transfer functions in patients with cochlear implants
Authors: Shannon Robert V.
Published: October 2005

Thresholds for the detection of amplitude modulation were measured in cochlear implant patients as a function of modulation frequency. Three types of threshold measures were taken: detection of amplitude modulation, detection of low-frequency sinusoidal current waveforms, and detection of beats in two-tone complexes. The temporal modulation transfer function (TMTF), defined as the plot of modulation detection thresholds as a function of modulation frequency, show low-pass filter characteristics with similar cutoff frequencies for all three tasks. The similarity of these three measures suggests a common temporal mechanism. While modulation detection differs somewhat in normal-hearing and implanted listeners, both exhibit the same general characteristics. The TMTFs are low pass with a cutoff frequency near 70 Hz for normal-hearing listeners and near 140 Hz for implanted listeners. Patients with cochlear implants can best detect temporal modulation at modulation frequencies below 300 Hz, and are most sensitive to 80- to 100-Hz modulation. At high carrier levels many implant patients could detect smaller modulation amplitudes than normal-hearing listeners, a finding that is consistent with the smaller intensity DLs for some implanted listeners at high levels. These results demonstrate that, while implant listeners cannot discriminate steady-state, high-frequency stimuli, speech information might be conveyed by the envelope of the high-frequency components of speech.
Mixed spectral representation—Formants and linear predictive coding
Authors: Olive Joseph P.
Published: October 2005

A cascade formant model is well suited to describe certain speech segments, such as vowels and vowel-like sounds. The formant model is also useful because the relationship between formants and the vocal tract configurations are well understood; however, this model is not adequate for other speech sounds, such as stops, fricatives, nasals, etc. On the other hand, LPC (linear predictive coding) analysis, of sufficiently high order, can adequately describe the spectrum of any speech sound, but the relationship between the LPC parameters and the spectrum or vocal tract configuration is not obvious. This paper describes a speech analysis/synthesis scheme that uses both formants and LPC parameters for different sections of a speech signal. Thus, in some regions, the benefit of the formant model can be utilized, while in other regions, the LPC representation can be used to obtain a good description of the speech spectrum. The analysis algorithm resolves the problem of discontinuities that arise from using the two different spectral representations. When provided with the same multipulse signal, the method of speech analysis described in this paper produces resynthesized speech of the quality of multipulse LPC.
Modeling phoneme perception. II: A model of stop consonant discrimination
Authors: van Hessen A. J. , Schouten M. E. H.
Published: October 2005

Combining elements from two existing theories of speech sound discrimination, dual process theory (DPT) and trace context theory (TCT), a new theory, called phoneme perception theory, is proposed, consisting of a long-term phoneme memory, a context-coding memory, and a trace memory, each with its own time constants. This theory is tested by means of stop-consonant discrimination data in which interstimulus interval (ISI; values of 100, 300, and 2000 ms) is an important variable. It is shown that discrimination in which labeling plays an important part (2IFC and AX between category) benefits from increased ISI, whereas discrimination in which only sensory traces are compared (AX within category), decreases with increasing ISI. The theory is also tested on speech discrimination data from the literature in which ISI is a variable [Pisoni, J. Acoust. Soc. Am. 36, 277–282 (1964); Cowan and Morse, J. Acoust. Soc. Am. 79, 500–507 (1986)]. It is concluded that the number of parameters in trace context theory is not sufficient to account for most speech-sound discrimination data and that a few additional assumptions are needed, such as a form of sublabeling, in which subjects encode the quality of a stimulus as a member of a category, and which requires processing time.
A three-dimensional analysis of acoustic propagation in a penetrable wedge slice
Authors: Deane Grant B. , Tindle Chris T.
Published: October 2005

A model for the three-dimensional acoustic field in a penetrable wedge with isovelocity sound-speed profiles and a harmonic, point source is developed using the method of source images. The model is used to compute the field in a plane normal to the wedge apex (a wedge ‘‘slice’’). A new loss term due to three-dimensional effects is derived and investigated. The field in the sediment of a wedge slice is computed and the mode penetration angles are compared with those obtained by Jensen and Kuperman [J. Acoust. Soc. Am. 67, 1564–1566 (1980)] using the narrow angle parabolic equation and Jensen (private communication) using a coupled mode calculation.
Multiple scattering by many bounded obstacles in a multilayered acoustic medium
Authors: Lim Raymond
Published: October 2005

Recently, a multicentered, transition (T) matrix formalism was suggested for scattering calculations involving many bounded obstacles in homogeneous fluid and solid hosts [Lim and Hackman, J. Acoust. Soc. Am. 91, 613–638 (1992)]. In this paper, an extension of that formalism to the problem of multiple scattering by many bounded obstacles arbitrarily distributed in a plane-stratified acoustic medium is presented. Hackman and Sammelmann [J. Acoust. Soc. Am. 84, 1813–1825 (1988)] have given an elegant solution for scattering within a waveguide containing a single obstacle. The present extension is obtained by expanding the multiply scattered field from each obstacle within a layered fluid using their obstacle-waveguide T matrix. Obstacle-centered, outgoing eigenfunctions appropriate to the layered medium are used to expand the field scattered from each obstacle. Green functions of the layered medium are expanded in appropriate regular eigenfunctions to get the incident field coefficients required for the scattered field calculation. To complete the formulation in analogy to multiple scattering in an infinite, homogeneous medium, interactions are accounted for by matrices that translate the origin of these eigenfunctions among the obstacles present. The translation matrices are derived and incorporated into a transition supermatrix in the obstacle index. The resulting solution is formally exact to all orders of multiple scattering between the obstacles and between the obstacles and the layered host. Also, the formalism does not restrict the distribution of obstacles to a single layer and the method is simply extended to obtain the field scattered from infinite, periodic arrays insonified by plane waves in the stratified medium.
Sound scattering by rough elongated elastic objects. II: Fluctuations of scattered field
Authors: Stanton T. K. , Chu D.
Published: October 2005

Sonar echoes from unresolved features of rough objects tend to interfere with each other. Because of these interferences, properties of the echoes, such as its envelope level, will vary from realization to realization of stochastically rough objects. In this article, the nature of the fluctuations of the backscattered echo envelope of rough solid elastic elongated objects is investigated. A general formulation is initially presented after which specific formulas are derived and numerically evaluated for straight finite-length cylinders. The study uses both the approximate modal-series- and Sommerfeld–Watson-transformation-based deformed cylinder solutions presented in the first part of this series [T. K. Stanton, J. Acoust. Soc. Am. 92, XXX (1992)]. The fluctuations of the backscattered echo envelope are related to the Rice probability density function (PDF) and shown to depend upon σ/a and ℒ/L in the Rayleigh scattering region (ka≪1) and kσ and ℒ/L in the geometric region (ka≫1), where σ is the rms roughness, a is the radius of the cylinder, ℒ is the correlation length of the roughness, L is the length of the cylinder, and k is the acoustic wave number in the surrounding fluid. There are similarities shown between these fluctuations in the geometric region and those from rough planar interfaces. In addition, analytical expressions and numerical examples show that the fluctuation or ‘‘incoherent’’ component of the scattered field is random only in amplitude—its phase approaches a constant value, in phase with the mean scattered field, which needed to be taken into account in the formulation. Finally, applications of the theory developed in this article to backscatter data involving live marine shrimp-like organisms are discussed.
Distortion and high-frequency generation due to nonlinear propagation of short ultrasonic pulses from a plane circular piston
Authors: Baker Andrew C. , Humphrey Victor F.
Published: October 2005

A numerical finite-difference model for the prediction of nonlinear propagation has been adapted to examine the high-frequency components generated by short ultrasonic pulses. Comparisons are made in both the time and frequency domains between the model predictions and experimental measurements. The experimental measurements were obtained, in water, using a 1-mm-diam membrane hydrophone to sample the pressure field generated by a plane transducer (38 mm in diameter) that was driven by a diagnostic medical ultrasound system. The pulses generated were a few cycles long with a zero-crossing frequency of about 2 MHz and a maximum peak positive pressure of about 300 kPa. It is shown that the theoretical model can be used to provide accurate predictions (typically better than 10%) both on and off the acoustic axis for pulsed pressure fields in water. An important factor in obtaining good agreement is the initial characterization of the transducer and pulse.
The acoustic field of a near-surface source at intermediate distances: A simple result using matched asymptotic expansions
Authors: Myers Matthew R. , Kerschen E. J.
Published: October 2005

The method of matched asymptotic expansions is used to determine simple expressions for the acoustic field due to a source near a rigid boundary in an inhomogeneous medium. The observation distance is assumed to be large compared to the wavelength but short compared to the length scale over which the medium varies. Three asymptotic regions are identified: a local or source region, an outer or geometric-acoustics region, and a boundary layer containing an outer scattered field. The approach is illustrated in detail for the case of a simple source above a rigid surface in an environment for which the square of the index of refraction varies linearly with distance from the surface. Numerical comparisons show that, over a wide parameter range, the asymptotic result agrees well with the Hankel-transform solution for the linearly varying medium. The theory is then extended to account for more general media variations and sources with complex directivities.
An adaptive tracker for partially resolved acoustic arrivals with application to ocean acoustic tomography
Authors: Hippenstiel R. , Chaulk E. , Miller J. H.
Published: October 2005

Tracking the arrival time of identifiable, stable, and resolvable signals has been essential for ocean acoustic tomography. Resolvability is usually attained by having the separation between successive multi-path/mode arrivals be greater than the digit duration of a phase-encoded signal. An unresolved ray or mode can cause a local maxima in the correlator receiver output at a time corresponding to its arrival time. As the phase code is repeated and if these maxima occur often enough, the arrival may then be considered partially resolved and may be tracked. Here an application of the Widrow–Hoff least-mean-squares adaptive algorithm to the tracking of partially resolved mode arrivals measured in an acoustic tomography experiment carried out in Monterey Bay in 1988 is described.
Spectral and temporal weights in spectral-shape discrimination
Authors: Dai Huanping , Berg Bruce G.
Published: October 2005

The COSS analysis [B. G. Berg, J. Acoust. Soc. Am. 86, 1743–1746 (1989)] was used to estimate spectral and temporal weights of a three-component, amplitude-modulated stimulus in a spectral-shape discrimination task. In all experiments, the task of the observer was to detect an increment in the level of the center component. A spectral–temporal weight quantifies the relative influence of a spectral component on the decisions of an observer during a specified segment of the total stimulus duration. In the first two experiments, the signal was added to all three temporal segments of the center component. The ideal weights for each component should be the same across temporal segments. Spectral–temporal weights were obtained for four conditions with different stimulus durations. In general, the estimated weights for each component were not equal at different temporal segments. In the third experiment, the signal was added to only one of three segments of the center component. Ideally, weight patterns should have changed when the temporal position of the signal segment was altered. Two stimulus durations, 300 and 15 ms, were used. For the 300-ms condition, the signal was added to only the end segment, and for all three observers the weight patterns are different from that obtained in experiment 1 with the signal added to all segments. For the 15-ms conditions, altering the signal position changed the estimated weights for only one observer.
A ground-based narrow-band passive acoustic technique for estimating the altitude and speed of a propeller-driven aircraft
Authors: Ferguson Brian G.
Published: October 2005

The Doppler effect is the change in the observed frequency of an acoustic or electromagnetic wave due to the relative motion of source and observer. The acoustical Doppler effect is utilized here to estimate the altitude and speed of a propeller-driven aircraft. The acoustic energy emitted by the aircraft is received by a microphone located just above ground level. The acoustic spectrum of the aircraft is dominated by a spectral line corresponding to the propeller blade rate which is equal to the product of the propeller shaft rotation rate and the number of blades on the propeller. For the present experiment, the aircraft is flown at a constant altitude and speed over the microphone. A frequency estimation technique is applied to the acoustic data from the microphone so that the Doppler shift in the propeller blade rate can be observed at short time intervals during the aircraft’s transit overhead. Using the altitude and speed of the acoustic source as the variable parameters, a simple model is fitted to the observed variation of the blade rate with time; estimates of the aircraft’s altitude and speed correspond to a least-mean-squares curve fit of the model to the observations. These estimates are then compared with the actual altitude and speed recorded by the aircraft itself as it flew over the microphone at each of the nominated altitudes: 250, 500, 750, 1000, 1250, and 1500 ft, and at each of the nominated speeds: 150, 200, and 250 kn.
Signal detectors for random ocean media
Authors: Lourtie Isabel M. G. , Carter G. Clifford
Published: October 2005

This paper reports on acoustic signal detection in a stationary random multipath environment. The multipath transmission channel is modeled considering that both multipath time delay and attenuation coefficients characterizing the emitter/receiver transfer function are random variables with an a priori given distribution. Under the above condition, and assuming the signal-to-noise ratio (SNR) is either low or high, the likelihood ratio (LR) detector structure is developed, analyzed, and interpreted. A Monte Carlo study is also carried out. For low SNR conditions, the statistical behavior of the achieved processor is evaluated and compared to that of two classical detectors: (i) the standard detector derived based on a presumed known multipath channel structure, and (ii) the ad hoc detector developed for inaccurate multipath time delay modeling assumptions.
The use of the discrete Fourier transform to calculate the spatial and temporal response of line-driven, layer-wise homogeneous acoustically loaded panels
Authors: Wahl Thomas J. , Bolton J. Stuart
Published: October 2005

A numerical method for evaluating the spatial and temporal response of line-driven, acoustically loaded, damped panels is presented in this paper. Formal solutions to problems of this type are easily obtained using wave-number transform techniques. Here, it is shown that the inversion integral that defines the spatial response may be evaluated efficiently by using the fast Fourier transform algorithm to evaluate the inverse discrete Fourier transform. If desired, the temporal response may then be obtained by performing a further inverse transform. Numerical aspects of the inversion procedure are discussed briefly and guidelines are offered for the selection of spatial and temporal sampling rates and transform lengths. It is then shown that results obtained earlier by using contour integration can also be obtained by using the present technique if the transform parameters are chosen appropriately. The usefulness of the present procedure is then demonstrated through a number of examples. Both the transverse vibration of a water-loaded steel panel and the response of thin, aluminum panels are evaluated in a number of different configurations. In particular, it is demonstrated that the fast Fourier transform approach allows results to be calculated for configurations that are not amenable to classical techniques: e.g., layer-wise homogeneous systems involving a number of parallel elastic panels separated by fluid-filled channels and/or channels filled with porous material.
Intensity discrimination in forward masking
Authors: Zeng Fan-Gang , Turner Christopher W.
Published: October 2005

A nonmonotonic intensity discrimination function was recently reported in which a midlevel hump occurred for 25-ms sinusoidal standards ranging from 20 to 100 dB SPL and presented 100 ms after an intense narrow-band noise forward masker [F.-G. Zeng et al., Hear. Res. 55, 223–230 (1991)]. This paper provides additional data on how the midlevel hump is affected by three factors of forward masking: signal delay, masker level, and frequency. Specifically, just-noticeable differences (jnd’s) in intensity were obtained at signal delays of 50, 200, and 400 ms. Results show that at the midlevels the forward-masked intensity jnd’s did not recover to their unmasked values, even at the 400-ms signal delay. The longer the signal delay, the smaller this midlevel hump. This slow recovery of the midlevel jnd’s is consistent with the finding that low-spontaneous rate (SR) neurons have a slow recovery from forward masking [E. M. Relkin and J. R. Doucet, Hear. Res. 55, 215–222 (1991)]. The large midlevel effect decreased sharply as masker level was reduced from 90 to 60 dB SPL, and disappeared for masker levels less than 40 dB SPL. A frequency selectivity effect for the large midlevel jnd effect was also observed, as maskers with frequency components 2 to 3 oct away from the signal frequency did not affect the jnd’s. Overall, the present data are consistent with the hypothesis of Zeng et al. (1991) that low-SR neurons are involved in the midlevel hump of intensity discrimination in forward masking.
Material tailoring of structures to achieve a minimum radiation condition
Authors: Naghshineh Koorosh , Koopmann Gary H. , Belegundu Ashok D.
Published: October 2005

A strategy is developed for designing structures that radiate sound inefficiently in light fluids. The problem is broken into two steps. First, given a frequency and overall geometry of the structure, a surface velocity distribution is found that produces a minimum radiation condition. This particular velocity distribution is referred to as the ‘‘weak radiator’’ velocity profile. Second, a distribution of Young’s modulus and density distribution is found for the structure such that it exhibits the weak radiator velocity profile as one of its mode shapes. In the first step, a finite element adaptation of the integral wave equation is combined with the Lagrange multiplier theorem to obtain a surface velocity distribution that minimizes the radiated sound power. In the second step, extensive use of structural finite element modeling as well as linear programming techniques is made. The result is a weak radiator structure. When compared to a structure with uniform material properties, the weak radiator structural response is found to exhibit three important characteristics. First, the weak radiator structure shows lower vibration amplitude near its boundaries. Second, the weak radiator structure exhibits lower wave number content in the supersonic region. Third, the distribution of surface acoustic intensity on the weak radiator structure is very small at all the points along its surface. The effect of modal overlap on the performance of the weak radiator structures is found to be negligible. While the method employed here is general, the example of a simple beam radiating in a rigid baffle is used for the purpose of illustration.
Excitation of higher-order ultrasonic Lamb wave modes in piezoelectric plates
Authors: Jin Yu , Joshi Shrinivas G.
Published: October 2005

The excitation of higher-order ultrasonic Lamb wave modes by an interdigital transducer (IDT) deposited on a piezoelectric plate is investigated both theoretically as well as experimentally. Green’s function method of analysis is used to calculate the coupling of the IDT to the various modes. This is then used to calculate the performance of a Lamb wave delay line. Experimental results obtained on delay lines fabricated on 128° rotated Y-cut, X-propagating lithium niobate plates are compared with theoretical calculations. The resonant frequencies and time delays of the modes are found to be in fair agreement with calculated values. It is shown that delay lines fabricated on acoustically thin plates (h/λ<1, where h=plate thickness, and λ=acoustic wavelength) can efficiently excite Lamb waves at frequencies greater than 10 times the resonant frequency of the lowest-order mode.
Determination of macro- and micromechanical and interfacial elastic properties of composites from ultrasonic data
Authors: Chu Y. C. , Rokhlin S. I.
Published: October 2005

A self-reference ultrasonic bulk wave method for nondestructive measurement of elastic properties of ceramic matrix composites has been developed. The method has the advantage of minimizing the effect of geometrical imperfection of the sample. The experiment has been done on silicon carbide (SiC) fiber-reinforced reaction-bonded silicon nitride (Si3N4) matrix composites. The composite elastic constants are extracted from the experimental phase velocities using a nonlinear optimization procedure to find the best fit between experimental data and the solutions of the Christoffel equation. The effect of individual constituents on the overall composite properties has been investigated. The effects of porosity on the matrix properties and water saturation of pores on the immersion ultrasonic measurements are taken into account using a micromechanical model for two-phase particulate composites. This model is validated by experimental data. A microstructural model for analysis of elastic properties of ceramic matrix composites and their interfaces from experimental data is introduced. The fiber and the interface are modeled by effective fibers with anisotropic properties and a perfect bond between fiber and matrix. The properties of the effective fibers are extracted from the measured composite elastic moduli using a nonlinear optimization procedure. Shear and longitudinal elastic moduli of 3-μm-thick carbon-rich coatings are determined using measured effective and estimated actual elastic properties of the fibers.
Sound spatial correlations in shallow water
Authors: Wang Qin , Zhang Renhe
Published: October 2005

A method is presented for the estimation of the vertical and longitudinal correlations averaged over range and depths in a multipath channel. The resulting correlations are shown to be the integral of the vertical and longitudinal correlation factors weighted by the angular energy density. A correlation peak occurs when the receiver depth approaches either the source depth or its conjugate. The longitudinal correlation is shown to be reciprocal while the vertical is not. Numerical results are developed to gain additional insight into the physical features involved. Some field measurements of spatial correlations obtained in North China Sea are included.
Measured wave-front fluctuations in 1000-km pulse propagation in the Pacific Ocean
Authors: Duda T. F. , Flatté S. M. , Colosi J. A. , Cornuelle B. D. , Hildebrand J. A. , Hodgkiss W. S. , Worcester P. F. , Howe B. M. , Mercer J. A. , Spindel R. C.
Published: October 2005

A 1000-km acoustical transmission experiment has been carried out in the North Pacific, with pulses broadcast between a moored broadband source (250-Hz center frequency) and a moored sparse vertical line of receivers. Two data records are reported: a period of 9 days at a pulse rate of one per hour, and a 21-h period on the seventh day at six per hour. Many wave-front segments were observed at each hydrophone depth, and arrival times were tracked and studied as functions of time and depth. Arrivals within the final section of the pulse are not trackable in time or space at the chosen sampling rates, however. Broadband fluctuations, which are uncorrelated over 10-min sampling and 60-m vertical spacing, are observed with about 40 (ms)2 variance. The variance of all other fluctuations (denoted as low-frequency) is comparable or smaller than the broadband value; this low-frequency variance can be separated into two parts: a wave-front segment displacement (with vertical correlation length greater than 1 km) that varies substantially between rays with different ray identifiers, and a distortion (with vertical correlation length between 60 m and 1 km) of about 2 (ms)2 variance. The low-frequency variance may be explained as the effect of internal waves, including internal tides. The variance of the broadband fluctuations is reduced somewhat but not eliminated if only high-intensity peaks are selected; this selection does not affect the statistics of the low-frequency fluctuations.
Backscattering by a suspension of spheres
Authors: Thorne Peter D. , Campbell Stuart C.
Published: October 2005

Predictions of backscattering from a suspension of nominally spherical particles are compared with a series of experimental observations. Initially measurements were taken on single particles to establish the form function for the glass spheres employed and comparisons are made with calculations based on resonance scattering theory. The form function description of sphere scattering has been employed to describe the interaction of sound with a suspension of spheres, with first-order multiple scattering being included by accounting for the attenuation introduced by the presence of the suspension itself. The study is in part stimulated by the application of acoustic backscattering for measuring suspended sediment concentrations in the marine environment and some discussion is presented on this topic.
Method for transducer transient suppression. I: Theory
Authors: Piquette Jean C.
Published: October 2005

The problem of driving a transducer in such a way as to produce a tone burst of steady-state sound radiation in the surrounding fluid medium is considered. The goal is to determine the driving voltage waveform to apply to a transducer to produce an acoustic pressure waveform in the fluid that is a segment of a steady-state sine wave, beginning and ending at zero crossings of the sine, i.e., the usual turnon and turnoff transients are suppressed. The theoretical driving voltage waveform for a spherical transducer is shown to consist of a sum of a pedestal voltage, a ramp voltage, and a sinusoidal voltage that is phase shifted with respect to the sinusoid appearing in the fluid. Both theoretical and numerical calculations are given here. The following paper presents results of experimental measurements. The measurements were carried out on several spherical transducers (one of which was selected for presentation) and on an array of piezoelectric tubes. These experiments confirm the validity of the theory.
Method for transducer transient suppression. II: Experiment
Authors: Piquette Jean C.
Published: October 2005

Results of experiments that were conducted to investigate the validity of the theory presented in the preceding paper are given. The method was applied to a number of spherical piezoelectric sources, one of which was selected for presentation here, and to a source consisting of an array of piezoelectric tubes. A high degree of transient suppression was realized.
A 30-year experiment in the acoustical and musical development of violin-family instruments
Authors: Hutchins Carleen M.
Published: October 2005

The 30-year acoustical and musical development of the violin octet has shown that new instruments of the violin family can be constructed with fine tone and playing qualities based on acoustical parameters, free plate tuning, and skilled violin making. The frequency placement in relation to string tuning of the body-length air cavity mode (A1), originally called the ‘‘main wood’’ resonance, has been found to be the prime controlling factor differentiating overall tone quality of the violin from that of the viola, cello, and string bass. The frequency placement of the A0 cavity mode, originally labeled ‘‘Helmholtz’’ or ‘‘main air’’ resonance in relation to string tuning is secondary. For instruments smaller than the cello this A0 cavity mode frequency is controlled more by air volume than by compliance of the top, back, and sides (ribs). For cello and larger instruments the A0 mode frequency is controlled more by compliance of the top, back, and ribs than by air volume. Due to greatly increased compliance of the wooden walls of the basses particularly, it has been found structurally unsafe to make ribs shallow enough to place the A0 cavity mode seven semitones above the lowest note as our original scaling theory projected. The musical development of the violin octet and its potential for new sounds and compositions is discussed along with projections for its future in our musical culture.
Native language factors affecting use of vocalic cues to final consonant voicing in English
Authors: Crowther Court S. , Mann Virginia
Published: October 2005

Preceding vocalic information can cue final consonant voicing for native English speakers. This study examines subjects’ use of two vocalic cues, vocalic duration, and F1 offset frequency, as a function of two native language factors, experience with final stop consonants, and experience with phonemic vowel length. Native speakers of English are compared to native speakers of Japanese and Mandarin Chinese who are learning English as a second language. Experiment 1 measured the F1 offset frequency and vocalic duration in productions of ‘‘pod’’ and ‘‘pot.’’ Experiment 2 assessed identification of natural tokens of ‘‘pod’’ and ‘‘pot’’ with and without closure segments and bursts. Experiment 3 assessed categorization of synthetic ‘‘pod’’–‘‘pot’’ stimuli that systematically manipulated vocalic duration and F1 offset frequency. Native speakers of English showed the strongest implementation of and sensitivity to vocalic duration, Mandarin speakers showed significantly weaker effects, and Japanese speakers fell in between. Group-related differences in use of F1 offset frequency were smaller, and much clearer in the case of production than perception. It is hypothesized that a lack of experience with final consonants penalizes use of vocalic cues among the Japanese and Mandarin subjects, in general. The advantage of the Japanese subjects for use of vocalic duration further suggests a facilitation effect of experience with phonemic vowel length.
The hydroacoustics of a raindrop impact
Authors: Nystuen Jeffrey A. , Ostwald Leo H. , Medwin Herman
Published: October 2005

Raindrops produce sound underwater by two known mechanisms: a relatively low energy impact sound and a much stronger bubble sound when a bubble in trapped during the drop splash. Although the bubble sound dominates when it occurs, in other circumstances the impact sound is important. The impact sound has been studied in the laboratory using single drops falling at terminal velocity and with numerical simulation. In both instances, it is convenient to monitor the pressure field in the immediate vicinity of the drop impact. This ‘‘near-field’’ pressure contains acoustic and nonacoustic components. The acoustic components include an impulsive acoustic water hammer and internal resonances of the water drop itself. The nonacoustic component of the pressure field is part of the hydrodynamic establishment of the splash flow and should not be interpreted as acoustic energy. The two components have been separated in order to identify the far-field acoustic propagation.
Vertical directivity of ice cracking
Authors: Greening Michael V. , Zakarauskas Pierre , Verrall Ronald I.
Published: October 2005

This paper presents direct measurements and the results of modeling of the vertical directivity of ice-cracking events. Measurements were obtained over the frequency band 30–200 Hz on a 22-element vertical array deployed below the Arctic pack ice in 420 m of water. A total of 160 events spanning horizontal ranges of 40–2000 m and source angles of 1° to 80° below horizontal are analyzed. For the longer ranges (40 wavelengths or greater), the measured source pressure directivity, as determined from the pressure level at the 22 different angles, can be fitted accurately to a dipole. For the shorter range events, the directivity often approximates a dipole, but this pattern is usually perturbed by several peaks or troughs at varying angles. Finally, a consistent increase in pressure level of approximately 3 dB above the dipole pattern is observed near 60°–65°. This is due to the leaked longitudinal plate wave coinciding with the acoustic mode at these source angles.
Source localization using a reference wave to correct for oceanic variability
Authors: Mourad Pierre D. , Rouseff Daniel , Porter Robert P. , Al-Kurd Azmi
Published: October 2005

This paper describes a low-frequency, long-range acoustic propagation method for source localization. It is based on imaging techniques that remove the effects of adiabatic oceanic variability between an acoustic receiving array and an unknown source by combining measured data from the unknown source with measured data from a known reference source. At the heart of the concept is the realization that both sets of measured data are contaminated in the same way by the range-integrated effects of the ocean, for the stretch of ocean that they share between their positions and the receiving array. These contaminants can be made to cancel, leaving the integrated, and much smaller, effects of the oceanic variability between the reference source and the unknown source.
Scattering of Lamb waves at the edge of a semi-infinite plate embedded in water
Authors: Pareige P. , Luppé F. , Ripoche J.
Published: October 2005

An experimental study is presented of the scattering of Lamb waves at the end section of an elastic plane plate immersed in water. For antisymmetric modes as well as for symmetric ones, the amplitude of the radiated bulk wave in the water is recorded versus the angle of observation. In order to explain these patterns, a model is proposed that deals with the Lamb wave displacements inside the plate. The agreement between the theoretical and the experimental diagrams is quite good. The radiation pattern obtained for parameters corresponding to the crossing of two Lamb dispersion curves is also investigated.
Leaky axisymmetric modes in infinite clad rods. I
Authors: Simmons John A. , Drescher-Krasicka E. , Wadley H. N. G.
Published: October 2005

A detailed computational study is presented for the radial–axial modes— both leaky and nonleaky—in an infinitely clad isotropic rods. The complex phase velocities of leaky modes are located using an application of the argument principle. Particle orbits are determined, and leaky modes are shown to have an asymptotic leakage angle away from the interface. By using the homotopic methods of varying densities and elastic constants, clad-rod modes are compared with those in a bare rod. The topology of the clad-rod mode dispersion diagram differs qualitatively from that of a bare rod, even when the cladding has negligible density, with no velocity cutoffs and with wave mode knitting. Comparison is also given with modes occurring in a cladding without a rod present (a tunnel) and for a planar interface. Most leaky modes can be correlated with rod modes; only a limited number of tunnel modes exist. Energy flow contours within modes are also calculated. The local energy velocity, which generalizes group velocity, can vary considerably in the radial direction for bare rod modes. For leaky modes the contours are quite complex due to the cylindrical geometry, giving rise to apparent shift in wave position across the interface.
Reflection and refraction at a fluid–porous medium interface
Authors: Caviglia Giacomo , Morro Angelo , Straughan Brian
Published: October 2005

The problem of a plane wave, moving in a perfect fluid incident on a saturated porous medium, is investigated. The porous medium consists of a mixture of a compressible fluid and a compressible linear elastic solid. Attention is focused on the effect of porosity variation on the refraction and reflection wave properties. The model adopted for the porous medium, which is based on the theory of mixtures, allows porosity variation via inclusion of an evolutionary equation to describe the porosity. A numerical example is included for a plane wave traveling in water incident on a kerosene-saturated sandstone.
The wave superposition method as a robust technique for computing acoustic fields
Authors: Jeans R. , Mathews I. C.
Published: October 2005

The wave superposition method has recently been advocated [Koopmann et al., ‘‘A method for computing acoustic fields based on the principle of wave superposition,’’ J. Acoust. Soc. Am. 86, 2433–2438 (1989)], as a reliable and accurate technique for computing the acoustic fields generated by arbitrary-shaped radiators; this study examines in depth the robustness and numerical stability of the method. The implementation of the method requires the placement of a finite number of point sources on a surface interior to the body of the radiator. The magnitude of these point sources can be evaluated in terms of the prescribed velocity distribution on the surface of the radiator. Once calculated, the magnitude of these point sources allow the pressure distribution exterior to the radiator to be evaluated. The first improvement made to the robustness of the method is the use of a hybrid combination of monopole and dipole sources; this modification allows the inherent problem of nonuniqueness of the method at certain frequencies to be overcome. Both discrete point and continuous source distributions are used to evaluate the method on a variety of test cases involving both spherical and prolate spheroid geometries. The prime motivation for using such a method is the avoidance of the singular integration inherent is the application of the normal boundary element methods, however, for the method to be successful, the resulting matrix approximations need to be well-conditioned. This numerical conditioning was found to be dependent not only on the position of the boundary and the source nodal points but also on the interpolation or the location of these sources on the retracted surface.