bluuebunny/crossref_metadata_2025 huggingface dataset:
A sparse integral equation method for acoustic scattering
Authors: Rosen Erik M. , Canning Francis X. , Couchman Luise Schuetz
Published: October 2005

Numerical calculations of acoustic scattering may be based on either differential equations or on corresponding integral equations. The differential equations generate a sparse matrix problem involving (possibly implicitly) an M by M matrix. Integral equations generate a matrix of size N by N, where N is much smaller than M. In the past the matrix resulting from an integral equation was necessarily full. A method for greatly reducing the storage required is presented here. The full N by N matrix resulting from the discretization of the Helmholtz integral is transformed into a sparse N by N matrix using the interaction matrix localization (IML) method. IML is a general method for integral equations describing wave phenomena. It produces a sparse matrix by partitioning the scatterer into several regions and using groups of basis functions each of which is nonzero over an entire region. The basis functions for a region are chosen so that each radiates a narrow beam in a different direction. The number of important physical interactions is greatly reduced. A large number of matrix elements have a relative magnitude of less than 10−4, and these are approximated by zero. This method is implemented as a modification to existing boundary element method codes. Details of the formulation are given for scattering from rigid bodies of revolution. Memory and storage requirements are reduced from N2 to approximately 100N, while the solution time for the matrix problem is reduced from O(N3) to O(N2). The solution method uses a sparse approximate inverse which allows an iterative method to converge to machine accuracy in less than five iterations. Results are given for scattering from a hemispherically endcapped cylinder of L/a=22, for ka=1 to ka=17.
Detection of mechanical changes to prosthetic heart valves by spectral analysis of valve closing sounds
Authors: Reynolds Karen J. , Stephen Richard O.
Published: October 2005

This study investigates the possibility of using spectral analysis of the closing sounds of a prosthetic heart valve to indicate minor changes to its mechanical state. Sounds are recorded in vitro in a large effectively anechoic tank of water, and the elastically mounted valve is actuated pneumatically within the water. This provides a noise-free environment for recordings. Analysis of the valve sounds is by spectral averaging and digital filtering, with each individual valve used to create its own filter. Results show that it is possible using this technique to detect reliably changes in the mechanical state of a valve, such as the addition of a small mass to the structure of the valve.
Acoustic scattering from fluid-loaded elastic shells: A Gaussian beam approach
Authors: Yang Yang , Norris Andrew N. , Couchman Luise S.
Published: October 2005

A new method is described for computing the acoustic far field scattered by a submerged smooth elastic thin shell. The total field is split into a sum of specular and leaky wave contributions. The latter arise from weakly radiating membrane waves that propagate globally over the structure, and are the focus of this work. The scattered leaky wave field is expressed, via a surface Helmholtz integral, as the sum of integrals along a finite number of Gaussian beams. The integral on each beam is then approximated as a line integral along the central ray of the beam. Finally, the far-field contribution from each line integral is reduced to a sum of stationary phase contributions. The derived asymptotic expression for the leaky wave field is uniformly valid for all observation directions. Difficulties associated with caustics and two-point ray tracing do not arise in the present formalism. A test of the method for a spherical shell shows that the numerical results agree well with the exact solution and the pure ray solution for kfa≳10, where kf is the fluid wave number.
A reflection grating that nullifies the specular reflection: A cone of silence
Authors: Feldman Eliot
Published: October 2005

This paper describes the geometry of an acoustical diffusor that nullifies the specular reflection of plane sound waves whose frequencies include a design frequency and all its harmonics up to a certain limit. The diffusor is a specially designed acoustical phase grating whose phase cancellation properties are governed by concepts from pure number theory going back to the great mathematician Karl Friedrich Gauss in the early 1800s and in the late 1920s to applications of the theory by Manfred R. Schroeder of Götingen and Bell Laboratories. Presented here is an exposition of Schroeder’s ground-breaking quadratic residue diffusor, using sufficient mathematical rigor to prove its astounding uniform reflection property, originally conceived for improved concert hall acoustics. It then becomes clear how to modify the quadratic residue sequences to what is called modified primitive root sequences to achieve the nullification of the specular reflection. Since the method, for any angle of incidence, results in cancellation in the specular direction and throughout an angular region on each side of the specular direction, the cancellations occur in a cone-shaped region. In particular, for normal incidence the sender of a signal sits in the cone—a cone of silence.
Reflection of plate waves at the fixed edge of a composite plate
Authors: Karunasena W. , Liew K. M. , Kitipornchai S.
Published: October 2005

An approximate method based on the wave-function expansion procedure has been used to solve the problem of reflection of time harmonic plane strain waves normally incident upon the fixed edge of a semi-infinite, uniaxially fiber-reinforced, composite plate of linearly elastic materials. Both symmetric and antisymmetric incident waves have been considered. The dispersion relation of the infinite plate has been solved through an approximate technique to obtain wave functions. The amplitudes of reflected waves have been determined by satisfying the fixed edge condition through the application of a variational principle. It is shown that the results agree well with known solutions for homogeneous isotropic plates. Numerical results are presented for a graphite/epoxy composite plate. The accuracy of the results is demonstrated through satisfaction of the principle of energy conservation and the reciprocity relations. The influence of fiber-direction elastic stiffness on reflection coefficients has also been studied.
The synthetic-analytic listening task for modulated signals
Authors: Yost William A. , Dye Raymond H. , Sheft Stanley
Published: October 2005

The synthetic-analytic listening task (SALT) developed by Dye and colleagues [Dye et al., J. Acoust. Soc. Am. 96, 2720–2731 (1994)] was applied to a task in which an amplitude-modulated tonal carrier was presented as a target during the standard stimulus. The standard stimulus was followed by a test stimulus in which the target along with another amplitude-modulated carrier (the distractor) was presented. The listener determined if in the test stimulus, the target (which was presented along with the distractor) was higher or lower in modulation depth than when the target was presented alone as the standard stimulus. The target and distractor were either 1- or 4-kHz carriers modulated at one of ten depths of modulation during the test stimulus at modulation rates ranging from 4 to 64 Hz. SALT was used to estimate the relative weight listeners assigned to the target and distractor as a function of the difference between their modulation rates, both for target carrier frequencies above and for target carrier frequencies below the distractor carrier frequency. When the target and distractor were modulated at the same rate, the target and distractor weights were equal, indicating synthetic listening. When the target and distractor differed in modulation rate, the listener gave more weight to the target suggesting a form of analytic listening. The result demonstrate the applicability of SALT to studies of modulation and reinforce the claim that different spectral components modulated with the same modulation pattern are processed synthetically.
Comments on ‘‘Sound radiation from finite cylindrical coated shells, by means of asymptotic expansion of three-dimensional equations for coating’’ [J. Acoust. Soc. Am. 96, 277–286 (1994)]
Authors: McDaniel J. Gregory
Published: October 2005

The idea of expanding elastic variables in powers of a thickness coordinate is not new, having been employed by Bassett as early as 1890 [Philos. Trans. R. Soc. Ser. A 181, 433–480]. A variety of works over the past decade, which were heavily influenced by Mindlin [‘‘An Introduction to the Mathematical Theory of Vibrations of Elastic Plates,’’ A Monograph Prepared for U.S. Army Signal Corps Engineering Laboratories, Fort Monmouth, NJ (1955)], have established that such expansions should introduce readily identifiable approximations. McDaniel and Ginsberg [J. Acoust. Soc. Am. 90, 2341 (1991) and J. Appl. Mech. 60, 152–157 (1993)] successfully addressed this idea with displacement expansions used in conjunction with Hamilton’s principle. The resulting formulation avoids many of the assumptions and complications that appear in the recent asymptotic analysis by Laulagnet and Guyader [J. Acoust. Soc. Am. 96, 277–286 (1994)], including assumptions on thickness relative to radius and to characteristic wavelengths. Numerical results from any set of expansions should be studied for convergence by including more terms and evaluating changes in a suitable metric, a procedure that is absent in the recent work of Laulagnet and Guyader.
Experimental identification of a resonance due to the finite dimensions of a specimen subjected to an external acoustic excitation
Authors: de Billy M.
Published: October 2005

In the last four decades, a number of papers were devoted to the existence of an edge resonance phenomenon existing at a certain frequency as an acoustic pulse train is internally incident on the free edge of an elastic plate or rod. In this paper it is verified that a similar resonance phenomenon exists when an external-pulse wave interacts with a finite-dimension target immersed in a fluid.
Acoustic analysis of the closing sounds of implanted prosthetic heart valves
Authors: Reynolds Karen J. , Stephen Richard O.
Published: October 2005

Previous in vitro studies [K. J. Reynolds, Ph.D. thesis (1994); K. J. Reynolds and R. O. Stephen, J. Acoust. Soc. Am. 97, 60–68 (1995)] have shown that it is possible to detect minor mechanical changes to a prosthetic heart valve by acoustic analysis of the valve’s closing sounds. This current study investigates the sounds produced by prosthetic valves implanted in patients. To reduce signal distortion at the thoracic surface, recordings were made with the patient submerged in water. Results show that stable reproducible averaged spectra can be obtained from implanted valves provided recording conditions are kept constant. The respiration cycle does not affect the recorded spectrum.
Analysis of the glottal excitation of emotionally styled and stressed speech
Authors: Cummings Kathleen E. , Clements Mark A.
Published: October 2005

The problems of automatic recognition of and synthesis of multistyle speech have become important topics of research in recent years. This paper reports an extensive investigation of the variations that occur in the glottal excitation of eleven commonly encountered speech styles. Glottal waveforms were extracted from utterances of non-nasalized vowels for two speakers for each of the eleven speaking styles. The extracted waveforms were parametrized into four duration-related and two slope-related values. Using these six parameters, the glottal waveforms from the eleven styles of speech were analyzed both qualitatively and quantitatively. The glottal waveforms from each style of speech have been shown to be significantly and identifiably different from all other styles, thereby confirming the importance of the glottal waveform in conveying speech style information and in causing speech waveform variations. The degree of variation in styled glottal waveforms has been shown to be consistent when trained on one speaker and compared with another.
Reactive characteristics of partial screens for a sound source mounted in an infinite baffle
Authors: Lee Jun-Shin , Ih Jeong-Guon
Published: October 2005

An analytical method using the assumed acoustic modes at boundaries is constructed to understand the sound radiation from a source mounted in an infinite baffle and blocked by a rigid close fitting shield. Special attention is given to overcome the thin body problem of the screen. An algebraic equation is derived by using the eigenfunction expansion and orthogonality principle in which the acoustic pressures and particle velocities defined on each subdivided surface are expressed by separable coordinates. Change of the radiation impedance of the source due to shielding is evaluated and is verified by experiments. Other acoustical characteristics of the partial screen are investigated in connection with the change of radiation impedance and with geometrical parameters of the system. The results of the parametric study reveal that the close fitting shield may not be a good noise control element for a source radiating broadband noise, especially at low frequencies in the absence of absorbing materials. The analytical results can be useful in the conceptual design stage of partial screens for selectively attenuating the sound radiation from machinery surface in the mid and high frequencies and for designing improved loudspeaker systems at low frequencies.
Field study of noise-induced sleep disturbance
Authors: Fidell Sanford , Pearsons Karl , Tabachnick Barbara , Howe Richard , Silvati Laura , Barber David S.
Published: October 2005

Behaviorally confirmed awakenings were recorded during nighttime hours for periods of approximately one month in 45 homes of 82 test participants. Measurements of awakening and of both indoor and outdoor noise exposure were made for a total of 632 subject nights near a military airfield, 783 subject nights near a civil airport, and 472 subject nights in neighborhoods with community noise exposure of nonaircraft origin. Sound exposure levels of individual noise intrusions were much more closely associated with awakenings than long-term noise exposure levels. The slope of the relationship between awakening and sound exposure level was rather shallow, however. Although the present findings do not resemble those of laboratory studies of noise-induced sleep interference, they are in good agreement with the results of other field studies.
Fiber-optic microphone based on a combination of Fabry–Perot interferometry and intensity modulation
Authors: Zhou Chonghua , Letcher Stephen V. , Shukla Arun
Published: October 2005

A fiber-optic microphone based on a combination of Fabry–Perot interferometry and intensity modulation is described. The combination technique eliminates fringe counting ambiguity and provides a wide range of measurement of optical phase change without any complicated electromechanical devices. The experimental data are compared with the result of a theoretical analysis. The microphone has a flat frequency response from 20 Hz to 3 kHz with a high sensitivity of 1.6 rad/Pa. The dynamic range is more than 65 dB. The frequency response and sensitivity can be modulated by changing the size and surface tension of the membrane. The microphone can be easily implemented and can be made very small.
Hydrodynamic siren as a broadband underwater sound projector
Authors: Yoshikawa Shigeru , Koyano Kiyoshi
Published: October 2005

The siren mechanism is adapted to underwater uses for sound production. Such a hydrodynamic siren works as a powerful, broadband mixed sound projector as well as a less powerful, more noiselike sound projector. The broadband mixed sound consists of the harmonics due to the rotor rotation rate and the hydrodynamic cavitation noise. The cavitation noise level at rotor rotation is almost the same as that when the rotor is not rotated. The maximum acoustic pressure of a model siren is 189 dB re: 1 μPa at 1 m when integrating between 0 and 10 kHz, and 179 dB re: 1 μPa at 1 m as to one peak line spectrum. The siren gain attained by the rotation rate harmonics is approximated at about 20 dB. The maximum overall electro-acoustic conversion efficiency is estimated as 1.2% for the rotor–stator clearance of 0.15 mm and the applied water pressure of 8.2 kg/cm2, that is, 0.80 MPa. Since the siren has a dual hole configuration, a third set of harmonics is virtually derived from the greatest common divisor obtained from the numbers of holes in the two sets of holes (i.e., 8 holes and 20 holes give an effective virtual 4 holes). The radiation directionality and depth dependence of the model siren are also examined. The experimental results on the hydrodynamic cavitation noise at nonrotation of the rotor almost match those revealed in previous literature on the noise from cavitating water jets and hydrofoils. However, the results show a strong dependence of the spectrum level on the receiving position. More detailed knowledge on the cavitating jet length, the bubble concentration along it, the vibration of the surviving bubbles, etc., are needed to understand the hydrodynamic cavitation noise more intensively. Although the siren cannot avoid the harmonic generation due to the rotation rate, a siren as a noise maker is proposed by considering a random configuration of many holes and random occurrence of hole opening in one rotation period.
The propagation of Lamb waves in a plate bordered with a viscous liquid
Authors: Zhu Zhemin , Wu Junru
Published: October 2005

The dispersion equations of Lamb waves of a plate bordered with a viscous liquid layer or half-space viscous liquid on both sides have been derived. Numerical solutions of the dispersion equations related to sensing applications are presented.
Diffraction and pulse delay in a structured ocean
Authors: Draganov A. , Spiesberger J.
Published: October 2005

In many media, the wave speed can be decomposed into a smoothed field in space plus a residual, with a spatial average of zero, that contains structure at shorter scales. Because of diffraction, the smoothing scale plays a key role in determining which approximation of the wave equation yields the most accurate estimate of pulse delay. For oceanic sound-speed profiles which are smoothed to suppress fine structure, an order of 0.1-s discrepancy in travel time is found between ray theory and an exact solution over a 4000-km section for acoustic frequency near 50 Hz. This difference occurs because ray theory ignores diffraction whereas the wave equation incorporates diffraction. The difference in pulse delay accumulates primarily from focusing regions where the spatial scale of the pressure field and diffraction effects come into play. Due to scattering from fine structure in the ocean, the scale of focusing regions may sometimes be enlarged to be much larger than that in a smooth sound-speed profile. Then, diffraction may not significantly affect pulse delay, and rays traced through a smoothed sound-speed profile may yield more accurate estimates of pulse delay than exact solutions of the wave equation which represent the ocean with the same smoothed sound-speed profile.
Acoustic scattering from a fluid-loaded cylindrical shell with discontinuities: Double plate bulkhead
Authors: Cuschieri J. M. , Feit D.
Published: October 2005

The far-field acoustic scattered pressure from a fluid-loaded cylindrical shell with two internal plate bulkheads is determined from knowledge of the junction forces between the shell and the internal plate structures. Results are shown for the circumferential modes n equals 0 and 2. This paper follows a previous paper in which a single internal plate bulkhead was considered. The approach used to solve for the junction forces is the same as that used in the previous paper. However, the results for the far-field scattered pressure show interesting features that can be associated with the acoustic and structural interaction between the two bulkheads. The interaction is due to both acoustic coupling and structural coupling. The scattered pressure associated with the radial forces at the bulkheads show an interference pattern with high and low intensity regions. The high intensity regions correspond to locations with constructive interference between the components of the scattered pressure by each bulkhead, which have dipolelike radiation characteristics. The low intensity regions correspond to locations with destructive interference. The same type of interference pattern is obtained in the scattered pressure component associated with the radial bending moments. The components of the scattered pressure associated with the bending moment at each bulkhead have quadrupolelike radiation characteristics. However, the contributions of these components is small compared to the other contributions. The scattered pressure components associated with the supersonic, axial longitudinal, and tangential shear waves do not show much of an interference pattern and this is mainly attributed to the fact that the scattering from these supersonic waves has preferred directions of propagation. All components of the scattered pressure show areas of high intensity at very specific frequencies which can only be attributed to structural interaction through the shell between the two internal bulkheads. The far-field scattered pressure results are presented for both bistatic and monostatic scattering.
Nonaxisymmetric vibration and acoustic radiation of a submerged cylindrical shell of finite length containing internal substructures
Authors: Choi S.-H. , Igusa T. , Achenbach J. D.
Published: October 2005

A modal-based method is developed to analyze the acoustic radiation of axisymmetric submerged shells of finite length with internal substructures, subjected to nonaxisymmetric time-harmonic loads. In this method, a variational principle is used to determine the relationship between the surface pressure and displacement of the shell, and Lagrange multipliers are used to account for the connections between the shell and the substructures. Fourier series expansions are used to represent the circumferential dependence of the surface pressure and displacement. The method is demonstrated by an extended analysis of a cylindrical shell with hemispherical elastic endcaps containing circular bulkheads. The dominant flexural wave numbers are identified from helical wave spectra. It is shown that the wave numbers of the dominant flexural waves are the same as those found in an infinite, fluid-loaded cylindrical shell. The locus of wave numbers of the dominant flexural waves lies outside of the sonic cone for low to mid frequencies. However, it is shown that bulkheads can create amplification of the flexural waves with wave numbers within the sonic cone. This is confirmed by a computation of the net power radiated by the shell: The shell with bulkheads radiates more energy than the empty shell for ka≳0.5, where k is the acoustic wave number and a is the radius of the cylindrical shell.
Coupling between an undamped linear acoustic fluid and a damped nonlinear structure—Statistical energy analysis considerations
Authors: Soize Christian
Published: October 2005

This paper deals with the coupling between an undamped linear acoustic fluid occupying a bounded cavity of three-dimensional space and a damped nonlinear three-dimensional structure surrounding the fluid. There is no excitation source inside the fluid and a time-stationary stochastic loading is applied to the structure. The developments are made using the statistical energy analysis (SEA) methodology. Consequently, a modal approach is used to describe the coupled mechanical system. Since there is no damping inside the fluid, an explicit solution of the problem can be constructed. In this paper: (1) the underlying linear elastoacoustic model is presented; (2) one develops the canonical equation for a nonlinear structure coupled with a linear acoustic fluid; (3) the stationary response of the coupled system is constructed and the explicit expression of the unique invariant measure is given; (4) the energy parameters of the acoustic cavity and the nonlinear structure are introduced and their statistical mean values and their statistical dispersions are calculated; (5) the mean power balance of the coupled system and the mean energies of each component are studied; (6) finally, one gives a simple two-dimensional example consisting of a nonlinear string coupled with a two-dimensional fluid cavity having an arbitrary shape.
A biologically inspired controller
Authors: Carneal James P. , Fuller Chris R.
Published: October 2005

A biologically inspired control approach for reducing vibrations in distributed elastic systems has been derived and experimentally verified for narrow-band excitation. The control paradigm approximates natural biological systems for initiating movement, in that a low number of signals are sent from an advanced, centralized controller (analogous to the motor cortex of the brain) and are then distributed by local simple rules to multiple control actuators (analogous to muscle fiber). Both theoretical and experimental investigations of three different local rules were carried out including a stability analysis for reducing beam vibrations. In general the results have demonstrated that the biological control approach has the potential to control multimodal response in distributed elastic systems using an array of many actuators with a reduced order main controller. Thus significant reductions in control system computational complexity have been realized by this approach.
Modeling of piezoelectric ceramic vibrators including thermal effects. Part I. Thermodynamic property considerations
Authors: Moon Won-kyu , Busch-Vishniac Ilene J.
Published: October 2005

The thermodynamic characteristics of piezoelectric ceramics are investigated by considering two thermodynamic material property models: isentropically linear and isothermally linear models. Those two models are two possible interpretations of the data on temperature-dependent linear coefficients of piezoelectric ceramics. Thermodynamic differences of the two models are examined and effects of the thermo–electro–mechanical couplings are evaluated in examples. Application of the thermo–electro–mechanical model to PZT4 shows that the difference observed in the piezoelectric constants obtained by static and dynamic measurements cannot be explained by the difference between isothermal and isentropic processes.
Modeling of piezoelectric ceramic vibrators including thermal effects. Part II. Derivation of partial differential equations
Authors: Moon Won-kyu , Busch-Vishniac Ilene J.
Published: October 2005

The partial differential equations for a piezoelectric ceramic body are derived to describe thermal as well as mechanical and electrical responses. Those can include conduction heat transfer, mechanical and electrical dissipation, thermal expansion, and pyroelectricity. The derived differential equations are so complicated that it is almost impossible to reduce them into a minimum independent set of differential equations. A simple one-dimensional case of the thickness vibrator with thermal effects is considered and an approximate model is proposed.
Longitudinal guided wave propagation in a transversely isotropic rod immersed in fluid
Authors: Nagy Peter B.
Published: October 2005

The propagation of longitudinal guided waves in fluid-loaded transversely isotropic rods has been investigated based on the superposition of partial waves. The numerical results indicate that fluid loading causes not only significant attenuation via energy leakage into the fluid but also strongly affects the phase velocity of the modes in certain frequency ranges. There is an apparent ‘‘mode switching’’ between the two lowest-order modes when the rod is loaded by a relatively high-density fluid. This phenomenon is analogous to the anomalous topology previously observed in the Lamb wave spectra of low-density water-loaded plates.
Ultrasonic attenuation and grain-size evaluation using electromagnetic acoustic resonance
Authors: Ogi Hirotsugu , Hirao Masahiko , Honda Takashi
Published: October 2005

Electromagnetic acoustic resonance is applied for determining the frequency dependence of the ultrasonic attenuation and the average grain size of low-carbon steels. Use of a noncontacting electromagnetic acoustic transducer (EMAT) makes it possible to isolate the attenuation within the plate specimens. The method relies on the Lorentz force mechanism to couple the EMAT to the specimen surfaces and then eliminates the other losses, which may otherwise occur with the contacting piezoelectric transducers. The measurement is independent of the EMAT used, the specimen thickness, the surface condition, the lift-off, etc., and is stable because of the noncontacting nature. First, the resonant frequencies are measured, to the accuracy of 10 Hz, by sweeping the operating frequency and obtaining the amplitude spectrum over a band in the 0.5- 20-MHz range. The ringing signals are excited and received by a shear wave EMAT and then processed with a superheterodyne receiver. Second, the attenuation coefficient as a function of the resonant frequency is determined. At each resonant frequency, the output signal rings down exponentially with time and the attenuation coefficient is obtained from the time constant by fitting an exponential decay to them. After correcting for the diffraction effect, the average grain size is obtained from the fourth-power term in the frequency dependence. The final results are favorably compared with the average of the three-dimensional grain-size distribution of steels.
Spectral super-element approach to range-dependent ocean acoustic modeling
Authors: Schmidt Henrik , Seong Woojae , Goh Joo Thiam
Published: October 2005

The spectral super-element approach uses a hybridization of finite elements, boundary integrals, and wave-number integration to solve the Helmholtz equation in a range-dependent ocean environment. The range-dependent ocean is divided into range-independent sectors or super-elements. Wave-number integral representations can be derived for an influence matrix representing the relation between displacement and pressure expansions on the vertical boundaries. The integration kernels are determined very efficiently by the direct global matrix method in combination with a numerical quadrature scheme. The unknown expansion coefficients are then found by matching the boundary conditions of continuous displacement and stress between the sectors, with the acoustic field following by evaluating the wave-number integrals within each sector, e.g. using the FFP technique. Two different boundary matching schemes are applied. One solves the global coupling problem incorporating all multiple scattering. A second, more efficient approach applies a single-scatter approximation at each vertical sector boundary, allowing for a marching solution. Numerical solutions to a series of canonical benchmark problems are given and compared to solutions obtained by other numerical approaches such as parabolic equations and coupled modes.
Pseudo-Doppler resonance phenomena in continuous wave scattering from evolving intermediate bubble plumes
Authors: Gragg Robert F. , Wurmser Daniel
Published: October 2005

An analytic expression is found for the scattered spectrum that is produced when a model dynamic bubble plume is ensonified by a continuous wave (cw) signal. The plume is of the ‘‘intermediate’’ type—with an interior sound speed well below that in the surrounding water—and thus exhibits sub-kHz internal resonances. These are assumed to be of a simplified Breit–Wigner type and their time dependence is shown to produce Doppler-like phenomena in the scattered spectrum. These ‘‘pseudo-Doppler’’ features are related to the parameters that specify the target plume’s time evolution. Conclusions are supported by comparison with the results of an exact numerical scattering calculation.
Signal modeling in reverberant environments with application to underwater electroacoustic transducer calibration
Authors: Ainsleigh Phillip L. , George James D.
Published: October 2005

Methods are introduced for modeling acoustic signals in reverberant environments. The application considered is stepped-sinusoid testing of underwater electroacoustic transducers in facilities where boundary reflections arrive at the hydrophone before the steady-state response of the transducer under test can be observed directly. The new methods are based on least-squares estimation of parameters in signal models composed of weighted sums of exponential functions. In the first method, only the pre-echo transient response is modeled. In the second method, a multipath model is used to represent the direct signal and the reflections. In addition, a new Prony-type method is introduced for generating initial pole estimates from the pre-echo portion of the response, and model constraints are introduced into the least-squares error functional to allow optimization of the time-of-arrival parameters. The new methods are used to calibrate a low-frequency resonant tonpilz projector in a small pressurized tank. These results are compared to results obtained using conventional methods in a large lake where the echo-free reception time is long enough to directly observe the steady-state response. Excellent agreement is demonstrated.
A simple iteration scheme for the computation of decay constants in enclosures with diffusely reflecting boundaries
Authors: Kuttruff H.
Published: October 2005

This paper describes a procedure for the exact determination of the decay constant and hence of the reverberation time of enclosures with diffusely reflecting boundaries. It is based on the integral equation which describes the energy propagation in such rooms under the condition of exponential decay. In contrast to Gilbert’s well-known method, the decay constant is determined by an iterative solution merely of that integral equation. Some typical results for rectangular rooms are presented. Depending on the distribution of sound absorbing areas, considerable differences between reverberation times after Sabine’s equation, on the one hand, and the present method, on the other, are observed. Furthermore, the question to what extent the applicability of the procedure is restricted by the assumption of diffuse wall reflections is discussed.
The equality of volume displacements in the inner ear windows
Authors: Kringlebotn Magne
Published: October 2005

The equality of volume displacements in the inner ear windows is commonly assumed. In the present work this assumption is experimentally verified. The stapes is given a known displacement. The volume displacement of the round window is determined by measuring the sound pressure set up in a tube cemented to the round window. Inner ears of pigs have been used in the investigation. Supplementary measurements on one human temporal bone have been performed. The equality of the volume flows in the inner ear windows is also supported through an analysis of earlier measurements of the round window displacement for a given sound-pressure level at the eardrum.
Individual differences in simultaneous masking with random-frequency, multicomponent maskers
Authors: Neff Donna L. , Dethlefs Theresa M.
Published: October 2005

Individual differences were examined for 49 listeners in a simultaneous-masking task with random-frequency, multicomponent maskers and a 1000-Hz signal. Across conditions, the maskers were broadband noise or complexes of 2–100 sinusoids whose frequencies were randomly chosen with each presentation. Maskers were equal rms waveforms, presented at 60 dB SPL. Thresholds for the multicomponent maskers spanned a range of up to 59 dB across listeners within conditions without distinct groupings. When divided into quartiles, mean thresholds for listeners in the lowest quartile increased monotonically with the number of masker components and peaked below values produced by broadband noise. Listeners in the upper quartile had nonmonotonic functions with a broad peak around 10–20 components, with values above those produced by broadband noise. Quiet thresholds and masked thresholds for the broadband-noise masker did not distinguish ‘‘high-’’ from ‘‘low-threshold’’ groups. Lowering masker uncertainty (frequencies randomized between but not within trials) or introducing temporal differences by shortening the signal both improved performance by as much as 40 dB, dependent on the masking produced with maximum uncertainty. Training effects within experiment (excluding an initial training period) were examined for all listeners and for five listeners across two consecutive experiments. Eleven of forty-nine listeners (22%) showed systematic improvement averaging 12 dB within experiment, independent of high or low original thresholds. For the five tested longer, four improved by 5 dB or more in at least one condition, but the change in performance occurred primarily during initial training for the second experiment. The large individual differences documented present a challenge to the development of models for masking produced by masker-frequency uncertainty.
Recognition of amplitude-modulation patterns in the presence of a distractor. II. Effects of dichotic presentation and unmodulated distractors
Authors: Takeuchi Annie H. , Braida Louis D.
Published: October 2005

Listeners indicated which of two comparisons had the same pattern of amplitude modulation as a target signal when distractors were presented simultaneously with the comparisons. The frequency separation between distractors and comparisons was either narrow or wide. Distractors were either modulated independently of the comparisons, comodulated with the comparisons, or unmodulated. At wide frequency separations, none of the distractors interfered significantly with modulation comparison, relative to performance with no distractors. At narrow frequency separations, comodulated distractors produced less interference than did independently modulated distractors. Unmodulated distractors also produced some interference. There was no difference between diotic presentation and dichotic presentation, in which distractors were presented to the opposite ear from targets and comparisons. Implications for the presentation of multiple envelope signals derived from different spectral regions of a speech signal to convey speech to hearing-impaired listeners are discussed.
Infants require low-frequency energy to hear the pitch of the missing fundamental
Authors: Clarkson Marsha G. , Rogers E. Christine
Published: October 2005

The present experiment assessed 7- to 8-month-old infants’ perception of pitch for harmonic tonal complexes containing either low- or high-frequency energy. In a visually reinforced, operant head turn procedure, infants first learned to discriminate two harmonic tonal complexes based on missing fundamental frequencies of 160 and 200 Hz. After learning this basic task, infants were presented with spectrally varying harmonic tonal complexes that contained either resolvable, low-frequency energy, or unresolvable, high-frequency energy. Infants learned to categorize the low-frequency signals according to the pitches of their missing fundamental frequencies but failed to categorize the high-frequency signals. These results suggest that infants require low-frequency, resolvable energy to hear the pitch of the missing fundamental.
On the feasibility of using neural nets to derive hearing-aid prescriptive procedures
Authors: Kates James M.
Published: October 2005

A neural net is a ‘‘black box’’ information processing system that can be used for pattern matching, optimal prediction, or functional approximation. A neural net requires a minimal amount of a priori knowledge about the problem to be solved, but can require large amounts of data to converge to a solution. For a hearing-aid fitting procedure, a multilayer perceptron net was trained to generate an optimum match between a set of input pure-tone audiograms and the corresponding best frequency response and gain for each subject. The feasibility of using neural nets to select hearing-aid response characteristics was tested using both simulated and real audiometric data. The simulation results indicate that a neural net can be successfully trained to reproduce a fitting rule such as the NAL-R procedure, and that a minimum of about 50 sets of audiometric response data are needed for the net to converge to a generalized solution. When used to predict, from the pure-tone audiograms, the best frequency response characteristics determined for subjects having severe-to-profound hearing losses, the neural net was more accurate than the NAL-R fitting procedure derived from the same data.
Optimum distributed constant false alarm rate detection of weak signals
Authors: Blum Rick S. , Kassam Saleem A.
Published: October 2005

A set of sensor detectors receive observations that may contain a zero-mean random signal of unknown amplitude. These observations also contain additive narrow-band non-Gaussian noise-plus-clutter with an unknown scale parameter. A constant false alarm rate distributed signal detection scheme is proposed that is optimized under weak signal conditions. This scheme assumes that a set of noise-plus-clutter-only reference samples are available at each sensor, and that these are used to provide an estimate of the unknown scale parameter. Each sensor processor uses the locally optimum test based on observing the scalar quantity that results from dividing the observation under test by the sensor’s scale parameter estimate.
Scattering of sound from a spatially distributed, spherically symmetric source by a sphere
Authors: Morris Philip J.
Published: October 2005

General expressions are derived for the scattering of sound from a spatially distributed, spherically symmetric source by rigid and nonrigid spheres. The incident field is determined using a Hankel transform for spherically symmetric variables. The scattered fields are determined by matching the total pressure and normal velocity at the surface of the sphere. Examples of the total and scattered fields are given for a ball source and a spherically symmetric source with a Gaussian spatial distribution. These solutions are compared with results for a point source.
Improved equivalent fluid approximations for a low shear speed ocean bottom
Authors: Zhang Z. Y. , Tindle C. T.
Published: October 2005

The acoustic reflection coefficient for a homogeneous fluid over a homogeneous solid with a low shear speed can be well approximated by replacing the solid with a fluid with suitably chosen parameters. It is shown that previous expressions for the density of this equivalent fluid can be replaced with a single expression which covers a wider range of practical cases. It is further shown that the use of a complex density gives an equivalent fluid which closely reproduces the reflection coefficient of typical soft solid seabeds.
Efficient computation of sound field above ground in horizontally stratified media using a Wentzel–Kramers–Brillouin-type approximation with Airy functions
Authors: Li Y. L.
Published: October 2005

Conventional fast field programs model a general refractive index profile with a system of horizontal layers. The choice of layer thickness and number of layers depends on frequency, range, and intrinsic properties of the refractive index profile. These constraints result in excessive computation time for many practical cases. To avoid the long run times associated with the layered model, a Wentzel–Kramers–Brillouin-type (WKB) approximation with Airy functions has been applied to the efficient computation of the height-dependent acoustic pressure. Numerical results demonstrate that the new fast field program can reduce the computer time about 50-fold. For higher frequencies, the new fast field program can save more computer time.
Sonic boom propagation through a realistic turbulent atmosphere
Authors: Boulanger Patrice , Raspet Richard , Bass Henry E.
Published: October 2005

A model of the turbulent atmosphere based on the von Karman spectrum is used in conjunction with a scattering center-based model to simulate sonic boom propagation. The distribution of rise times and peak overpressures predicted by the model are compared to those measured during a field test. Calculated rise times increase in the presence of turbulence, but the computed shift of the distribution toward higher values is less than measured. The predicted distribution of peak overpressure underpredicts the shift in overpressure to lower values displayed in the measured distribution. This underprediction is consistent with the rise time prediction. Future work will investigate the effect of anisotropic turbules on sonic boom propagation.
An interferometric technique for B/A measurement
Authors: Everbach E. Carr , Apfel Robert E.
Published: October 2005

An isentropic phase method is described for measuring in vitro the acoustic nonlinearity parameter B/A of several aqueous buffers, protein solutions, lipid oils, and emulsions. The technique relies upon the use of an acoustic interferometer to measure the small changes in sound speed that accompany a rapid hydrostatic pressure change of between one and two atmospheres. Average accuracies of 0.85% are attainable with this method.
Measurements of harmonic generation in a focused finite-amplitude sound beam
Authors: Averkiou Michalakis A. , Hamilton Mark F.
Published: October 2005

Measurements of harmonic generation in the sound field radiated by a focused circular piston source are compared with numerical calculations based on the nonlinear parabolic wave equation. The large dynamic range and high spatial resolution of the measurements enable precise comparisons to be made with the theoretical predictions.
Nonlinear distortion of finite-amplitude ultrasonic waves investigated by optical heterodyne interferometry
Authors: Jia Xiaoping , Adler Laszlo , Quentin Gérard
Published: October 2005

The study of asymmetrical patterns of the light diffracted by ultrasonic waves has been utilized in the last decades to investigate ultrasonic wave distortions caused by the nonlinearity of the medium. In contrast to the investigation of diffraction patterns in space, a novel optical method is proposed in this work to analyze, in the frequency domain, the phase modulation (related to the Raman–Nath parameter) of the probe beam. Using a heterodyne interferometric method, the effects of ultrasonic waves are described as sideband generations (Doppler shift) about a central frequency (optical heterodyning) in the frequency spectrum of the photocurrent. Asymmetry resulting from nonlinear effects was observed upon the spectrum envelope. This effect increases both with ultrasonic intensity and with propagation distance. Experimental results obtained in water confirmed qualitatively the theoretical analysis which includes the second and third harmonics in the formulation.
Acoustic scattering in three-dimensional fluid media
Authors: Chandra Kavitha , Isler Sylvia K. , Thompson Charles
Published: October 2005

The scattering of acoustic waves from three-dimensional compressible fluid scatterers is considered. Particular attention is paid to cases where the scatterers have moderate magnitude in compressibility contrast and nondimensional wave number. The perturbation method based on Padé approximants developed by Chandra and Thompson [J. Acoust. Soc. Am. 92, 1047–1055 (1992)] is extended to allow the solution of problems in three dimensions. It is shown that the functional form afforded by the Padé approximant model allows one to represent and evaluate the characteristic resonances and mode shapes of the scattered pressure field. These modes are a function of the compressibility contrast and the frequency of the incident pressure wave. Numerical results are shown to compare favorably with analytical solutions for scattering from a sphere. The Padé approximant method is shown to be feasible for calculating the pressure scattered from an inhomogeneous distribution of scatterers as well as for determining internal resonance.