bluuebunny/crossref_metadata_2025 huggingface dataset:
Acoustical nonlinearity of an electroacoustic cell containing electrolyte
Authors: Tankovsky N.
Published: July 2002

The nonlinear mechanical properies of an electrolytic, electroacoustic cell have been analyzed. Three main nonlinear mechanisms are present. (1) The nonlinear electric current in a circuit with a time-varying capacitance of the electrical double layer, modulated by the applied electric voltage. (2) The nonlinear time dependencies of the ion charges and of the local conductance at the interface membrane solution, governed by a Boltzmann distribution of the ion concentration. (3) The quadratic electrostatic forces of attraction, exciting a second acoustic harmonic. The interplay of these mechanisms is complicated. An analytical expression for the time dependence of the membrane displacements of the electroacoustic cell is obtained and the harmonics amplitudes are analyzed by numerical evaluations.
Vibration of annular sector plates from three-dimensional analysis
Authors: Liew K. M. , Ng T. Y. , Wang B. P.
Published: July 2002

Accurate three-dimensional elasticity solutions are presented for the free-vibration analysis of annular sector plates with arbitrary (but continuous) boundary conditions. The Ritz procedure is used to minimize the integral energy functional, which is formulated in a cylindrical polar coordinate system, in the derivation of the governing eigenvalue equation. The vibratory characteristics of annular sector plates with variations in boundary condition, sector angle, and thickness are examined. The accuracy of the method is validated through appropriate convergence and comparison studies. The first known results presented here provide a basis for understanding the physics of vibrations of annular sector plates and can be used to assess numerical results obtained from various refined two-dimensional theories.
Linear elastic properties of anisotropic open-cell foams
Authors: Sahraoui S. , Mariez E. , Etchessahar M.
Published: July 2002

Plastic foams are commonly used as sound-absorbing materials. These foams can exhibit a low-frequency resonant vibration of a skeleton where fluid damping is important. The two-phase material dynamic behavior is then described by the Biot equations. This paper examines the elasticity of these kinds of porous materials through their microstructure. The foam is modeled by a periodic network of elastic bars. It is shown that the orientation and distribution in space of the bars and their geometry control the macroscopic properties and the anisotropy. This study is an extension of a model developed for isotropic foams by Warren and Kraynick [J. Appl. Mech. 55, 341–346 (1988)].
Energy radiation from point sources whose duration of accelerated motion is finite
Authors: Levine H. , Gaunaurd G. C.
Published: July 2002

A detailed analysis is given of the energy and power measures associated with point sources which proceed along a rectilinear path in a prescribed and continuous manner that involves a limited period of acceleration. Attention is focused on monopole source types either singly or in pairs. The consideration of a single monopole precedes that of a “colliding” pair of such sources that have either equal or opposite source strengths. In all cases the angular and the joint angular and frequency distribution of the radiated energy, as well as the total radiated energy, are found at subsonic Mach numbers, and, for the paired sources, estimates are contingent on small Mach numbers. Numerical plots of the angular distributions are given, and applications of the analysis include the elementary modeling of the sound fields radiated by new aircrafts capable of completely reversing their course in minute distances.
The reflected and transmitted acoustic field excited by a supersonic source in a two media configuration
Authors: Kooij B. J. , Kooij C.
Published: July 2002

The acoustic wave field due to a supersonic motion of a rigid object over a half-space is investigated. The analysis presented leads to closed form expressions for the reflected and transmitted conical waves as separate contributions. The linearized acoustic field equations are applied to obtain representations for the fields in a combined Laplace–Fourier transform domain. To these representations, which are mapped into the proper form, we apply the Cagniard–de Hoop technique in order to find closed form time–domain solutions for the reflected and transmitted acoustic fields. Attention is focused on supersonic effects, so the analysis concentrates on application of the Cagniard–de Hoop technique to obtain closed form space–time domain expressions from the contributions of poles, appearing in the transform domain representation for the reflected and transmitted acoustic wave field. It turns out that these pole contributions, next to wave solutions of the conical type also can give rise to headwaves, associated with the reflected conical wave. Numerical results for the reflected as well as the transmitted conical wave field are presented for an air–sea configuration with supersonic source velocities up to MACH 5.
On the sampling conditions for reconstruction of an acoustic field from a finite sound source
Authors: Tabei Makoto , Ueda Mitsuhiro
Published: July 2002

A simple and accurate method for the estimation of ultrasonic transducer fields is developed. In the method, the angular spectrum is employed to evaluate the three-dimensional propagation from a measured plane to an arbitrary parallel plane. The implementation uses a discrete convolution that is described in detail. Relative to conventional spatial-frequency representations, the implementation of the angular spectrum method in this paper has the advantage of being free from artifacts, enabling sample spacing to be greater than one half wavelength, using memory efficiently, and interpolating the measured data. The loosened sampling requirement and natural interpolation of the method permit efficient reconstruction of the full three-dimensional acoustic field from a coarse sound pressure measurement on single plane.
Bell clapper impact dynamics and the voicing of a carillon
Authors: Fletcher N. H. , McGee W. T. , Tarnopolsky A. Z.
Published: July 2002

The periodic re-voicing of the bell clappers of the Australian National Carillon in Canberra provided an opportunity for the study of the acoustic effects of this operation. After prolonged playing, the impact of the pear-shaped clapper on a bell produces a significant flat area on both the clapper and the inside surface of the bell. This deformation significantly decreases the duration of the impact event and has the effect of increasing the relative amplitude of higher modes in the bell sound, making it “brighter” or even “clangy.” This effect is studied by comparing the spectral envelope of the sounds of several bells before and after voicing. Theoretical analysis shows that the clapper actually strikes the bell and remains in contact with the bell surface until it is ejected by a displacement pulse that has traveled around the complete circumference of the bell. The contact time, typically about 1 ms, is therefore much longer than the effective impact time, which is only a few tenths of a millisecond. Both the impact time and the contact time are reduced by the presence of a flat on the clapper.
Efficient calculation of two-dimensional periodic and waveguide acoustic Green’s functions
Authors: Horoshenkov K. V. , Chandler-Wilde Simon N.
Published: July 2002

New representations and efficient calculation methods are derived for the problem of propagation from an infinite regularly spaced array of coherent line sources above a homogeneous impedance plane, and for the Green’s function for sound propagation in the canyon formed by two infinitely high, parallel rigid or sound soft walls and an impedance ground surface. The infinite sum of source contributions is replaced by a finite sum and the remainder is expressed as a Laplace-type integral. A pole subtraction technique is used to remove poles in the integrand which lie near the path of integration, obtaining a smooth integrand, more suitable for numerical integration, and a specific numerical integration method is proposed. Numerical experiments show highly accurate results across the frequency spectrum for a range of ground surface types. It is expected that the methods proposed will prove useful in boundary element modeling of noise propagation in canyon streets and in ducts, and for problems of scattering by periodic surfaces.
Representations of sound that are insensitive to spectral filtering and parametrization procedures
Authors: Levin David N.
Published: July 2002

This paper describes representations of time-dependent signals that are invariant under any invertible signal distortion. Such a representation can be created by rescaling the signal in a nonlinear dynamic manner that is determined by recently encountered signal levels. Information that is encoded in such representations will be faithfully communicated in the presence of severe signal distortions, which may originate in the transmitter, receiver, or the channel between them. As in speech communication, the receiver is “blind” and need not characterize the form of the signal distortion, which remains unknown. The method is applied to analytical examples, acoustic waveforms of human speech, and the short-term Fourier spectra of a bird song. The results suggest that the rescaled representation of a sound is insensitive to the way its spectra have been filtered and parametrized, as long as those processes do not obliterate the differences between the various spectra in the sound. Finally, the possible “speaker” independence of these representations is explored in the context of a simple linear prediction model of vocal tracts with a single degree of freedom.
Nondestructive imaging of shallow buried objects using acoustic computed tomography
Authors: Younis Waheed A. , Stergiopoulos Stergios , Havelock David , Grodski Julius
Published: July 2002

The nondestructive three-dimensional acoustic tomography concept of the present investigation combines computerized tomography image reconstruction algorithms using acoustic diffracting waves together with depth information to produce a three-dimensional (3D) image of an underground section. The approach illuminates the underground area of interest with acoustic plane waves of frequencies 200–3000 Hz. For each transmitted pulse, the reflected-refracted signals are received by a line array of acoustic sensors located at a diametrically opposite point from the acoustic source line array. For a stratified underground medium and for a given depth, which is represented by a time delay in the received signal, a horizontal tomographic 2D image is reconstructed from the received projections. Integration of the depth dependent sequence of cross-sectional reconstructed images provides a complete three-dimensional overview of the inspected terrain. The method has been tested with an experimental system that consists of a line array of four-acoustic sources, providing plane waves, and a receiving line array of 32-acoustic sensors. The results indicate both the potential and the challenges facing the new methodology. Suggestions are made for improved performance, including an adaptive noise cancellation scheme and a numerical interpolation technique.
Factors affecting the performance of large-aperture microphone arrays
Authors: Silverman Harvey F. , Patterson William R. , Sachar Joshua
Published: July 2002

Large arrays of microphones have been proposed and studied as a possible means of acquiring data in offices, conference rooms, and auditoria without requiring close-talking microphones. When such an array essentially surrounds all possible sources, it is said to have a large aperture. Large-aperture arrays have attractive properties of spatial resolution and signal-to-noise enhancement. This paper presents a careful comparison of theoretical and measured performance for an array of 256 microphones using simple delay-and-sum beamforming. This is the largest currently functional, all digital-signal-processing array that we know of. The array is wall-mounted in the moderately adverse environment of a general-purpose laboratory (8 m×8 m×3 m). The room has a T60 reverberation time of 550 ms. Reverberation effects in this room severely impact the array’s performance. However, the width of the main lobe remains comparable to that of a simplified prediction. Broadband spatial resolution shows a single central peak with 10 dB gain about 0.4 m in diameter at the −3 dB level. Away from that peak, the response is approximately flat over most of the room. Optimal weighting for signal-to-noise enhancement degrades the spatial resolution minimally. Experimentally, we verify that signal-to-noise gain is less than proportional to the square root of the number of microphones probably due to the partial correlation of the noise between channels, to variation of signal intensity with polar angle about the source, and to imperfect correlation of the signal over the array caused by reverberations. We show measurements of the relative importance of each effect in our environment.
Coupling analysis of a matched piezoelectric sensor and actuator pair for vibration control of a smart beam
Authors: Lee Young-Sup , Gardonio Paolo , Elliott Stephen J.
Published: July 2002

This paper presents a theoretical and experimental study of the in-plane and out-of-plane coupling of a matched piezoelectric sensor/actuator pair bonded on a beam. Both the sensor and actuator are triangularly shaped polyvinylidene fluoride (PVDF) transducers and are intended to provide a compact sensor/actuator system for beam vibration control. The measured sensor–actuator frequency response function has shown an unpredicted increase in magnitude with frequency, which was found, to be due to in-plane vibration coupling. An analytical model has been developed to decompose the sensor–actuator response function into an in-plane contribution and an out-of-plane contribution. This in-plane coupling can limit the feedback control gains when a direct velocity feedback control is applied. A method called the jωs compensation method is proposed to identify the effect of the in-plane vibration coupling at low frequencies. Even after this compensation, however, there was unexpected strong out-of-plane coupling at even modes, which may have been caused by a lack of accuracy in the shaping of the PVDF sensor and actuator. Numerical simulations have confirmed the sensitivity of the matched sensor/actuator pair with shaping errors.
Phonological awareness of English by Chinese and Korean bilinguals
Authors: Chung Hyunjoo , Schmidt Anna , Cheng Tse-Hsuan
Published: July 2002

This study examined non-native speakers phonological awareness of spoken English. Chinese speaking adults, Korean speaking adults, and English speaking adults were tested. The L2 speakers had been in the US for less than 6 months. Chinese and Korean allow no consonant clusters and have limited numbers of consonants allowable in syllable final position, whereas English allows a variety of clusters and various consonants in syllable final position. Subjects participated in eight phonological awareness tasks (4 replacement tasks and 4 deletion tasks) based on English phonology. In addition, digit span was measured. Preliminary analysis indicates that Chinese and Korean speaker errors appear to reflect L1 influences (such as orthography, phonotactic constraints, and phonology). All three groups of speakers showed more difficulty with manipulation of rime than onset, especially with postvocalic nasals. Results will be discussed in terms of syllable structure, L1 influence, and association with short term memory.
Acoustic field in a cased well with a sectorial crossing channel
Authors: Lin Weijun , Zhang Chengyu , Wang Xiuming , Zhang Hailan
Published: July 2002

The crossing channel in a cased well is a vertical and sectorial column filled with fluid in the cement layer between the steel pipe and formation sometimes formed during well cementing, which is harmful to the well and must be detected. To study the possibility of detecting the crossing channel by using a traditional logging tool, an acoustic field generated by a monopole source in a cased well with a crossing channel of various angles is simulated by a 2.5-D finite difference method for the first time. The results of the 2.5-D finite-difference method for the cases of 0 or 360 deg are compared and consistent with that of the well-known real axis integration method. Snapshots of normal stress and synthetic time-domain waveforms are displayed. The 2-D spectrum in wave number and frequency domain is also calculated, where the influence of the channel is clearer than that in the waveforms. Numerical study demonstrated that a crossing channel can be detected and sized if its angle is greater than 30 deg, and larger offset and lower frequency source are favorable to detect and size the crossing channel. [Work supported by NSFC 19974059.]
Improved ping-to-ping cross-correlation methods for synthetic aperture self-calibration
Authors: Billon Didier , Fohanno Franck
Published: July 2002

Ping-to-ping cross-correlation (P2C2) methods, like DPC (Displaced Phase Center), are an efficient way to estimate motion-related parameters for synthetic aperture beamforming, as shown by several sonar sea trials performed recently. Their accuracy depends much on the space sampling rate of the synthetic aperture. Achieving large resolution gain implies decreasing by a factor up to 2 the travel speed with respect to the absolute upper limit L/2T. The paper reports on two new P2C2 schemes that greatly relax this constraint. ‘‘Auxiliary frequencies P2C2’’ performs on signals from two additional frequencies transmitted at two electronically swapped phase centers close to both real aperture ends, simultaneously with the main frequency used to form the synthetic aperture. ‘‘Hybrid P2C2’’ consists in estimating bearing shift by means of a 2D gyrometer and an auxiliary vertical array, rather than from the main horizontal array signals. The principles of these processings are described and analytical expressions for performance bounds are given. Sonar images from a new towed sidescan sonar for deep sea floor mapping, obtained by means of both new P2C2 schemes, are presented. 25 cm cross-range resolution is achieved up to 800 m range. Then the resolution gain exceeds 30.
Dynamic analysis, psychological and physiological evaluations of the visual environment
Authors: Soeta Yoshiharu
Published: July 2002

Attempts are made to apply preference theory for sound fields to visual fields. To investigate how the periodical flicker and movements in vertical and horizontal directions are preferred, preference judgments were conducted by paired-comparison tests. Results show that each stimulus has each pereference period. The scale value of preference is formulated approximately in terms of the 32 power of the normalized period of stimulus. It is interesting that this formulation corresponds to that of temporal factors in sound fields. Next, relationships between the subjective preference and the factors extracted from the autocorrelation function (ACF) and the cross-correlation (CCF) of the EEG and MEG alpha waves were investigated. Remarkably, preferred stimulus shows a significantly longer effective duration of the ACF, τe, of the alpha waves than that of less preferred stimulus. This tendency was also found in previous studies that varied the delay time of a single sound reflection and the reverberation time of a music sound field. Also, the preferred stimulus shows a significantly greater magnitude of the CCF between the alpha waves from different locations on the brain. Thus, a similar rhythm repeats over a wider range of the brain, in both space and time, under a preferred condition.

Thesis advisor: Yoichi Ando

Copies of this thesis written in English can be obtained from Junko Atagi, 6813 Mosonou, Saijo-cho, Higashi-Hiroshima 739-0024, Japan. E-mail address: atagi\@urban.ne.jp.
Direct optimization methods, ray propagation, and chaos. I. Continuous media
Authors: Mazur Martin A. , Gilbert Kenneth E.
Published: July 2002

In classical ray tracing, eigenrays between a source and receiver are determined by an initial value or “shooting” approach. The launch angles of rays from a source point are varied until the rays intersect the receiver endpoint. In nonseparable range-dependent environments, the ray paths can be chaotic, putting a fundamental limit on tracing rays by shooting methods. In the present paper, an alternative approach based on Fermat’s principle of minimum propagation time is discussed. Rather than minimizing the travel time integral indirectly, by deriving the Euler–Lagrange equations for the ray paths, so-called “direct methods” of minimization, taken from the calculus of variations, are employed. Previous authors have demonstrated that simulated annealing, a direct method, can be used to find eigenrays in a particularly chaotic ray tracing problem. In the present paper, two direct methods are applied to the calculation of eigenrays in continuous media: the Rayleigh–Ritz technique, a classical direct method, and simulated annealing, a Monte Carlo direct method. Direct methods are compared to shooting techniques, and some of the advantages and drawbacks of both methods are shown using both nonchaotic and chaotic examples.
Study on the vibrational characteristics of ultrasonic transducers using tapered piezoelectric ceramic elements
Authors: Mitra Rupa , Saksena T. K.
Published: July 2002

Any nonuniformity in the flatness of a crystal element used in an ultrasonic transducer may lead to significant variations in transducer response. An accurate estimation of such variations could obviously be a measure of the nonuniformity involved, whatever its extent may be. Studies are reported on the effect of nonparallelism between two major plane surfaces of the crystal element on transducer response by studying the normal displacement amplitude pattern and its distribution over one of the vibrating (plane) surfaces at resonance. Measurements are carried out in air using a phase-locked laser interferometry technique where the effect of tapering in disk thickness on the transducer performance is manifested through the variation in vibrational patterns. Results of these measurements are compared with those obtained from electrical (conductance) response to highlight the importance of the former. Other comparison measurements, such as the conventional method of determination of acoustic response and pulse waveforms of the radiated signals in water, are also reported as a function of tapering in disk thickness. A correlation is discussed between results obtained from different measurements.
Estimation of temperature gradient effects on the normalized surface impedance of soils
Authors: Raspet Richard , Sabatier James M. , Arnott W. Patrick
Published: July 2002

Ground impedance measurements are used for sound propagation predictions and to determine soil properties. Solar heating of the ground leads to significant temperature swings and gradients in the near surface soil. The equations of thermoacoustics are applied to estimate the magnitude of the temperature effects on the impedance and develop an approximate equation for the adjustment of measured impedance. Ambient temperature effects are shown to be significant; temperature gradient effects in soils are negligible. The theory is applicable to noise control applications where larger gradients may occur in sound absorbing materials.
On the standard deviation of change-in-impedance due to fuzzy subsystems
Authors: Lin Y. K.
Published: July 2002

The effects of attached multiple subsystems of uncertain properties on the behavior of a main system are investigated by modeling the natural frequencies of the subsystems as random points in the frequency domain. Both the mean and the standard deviation of the change-in-impedance, attributable to the subsystems, are computed without the usual assumption of “modal overlap.” It is shown that the standard deviation, which has been overlooked by most authors on this subject, can sometimes be greater than the mean. Thus the knowledge of the mean alone is inadequate to make engineering decisions.
Design of active structural acoustic control systems using a nonvolumetric eigenproperty assignment approach
Authors: Li Z. , Guigou C. , Fuller C. R. , Burdisso R. A.
Published: July 2002

Sound radiation of planar radiators such as beams and plates is known to be directly related to the velocity distribution over the structural surface at low frequencies. For example, nonvolumetric modes correspond to poor sound radiators for small k0a. In this work, to achieve significant sound attenuation in the low-frequency range, the SISO eigenassignment technique is used to modify the eigenproperties of a planar structure using structural actuators and sensors so that all the modes of the controlled structure are nonvolumetric. The main advantage of such an approach is that the design is independent of the disturbance characteristics (i.e., type, position, and frequency content) and does not require sensors in the radiation field. The design procedure for the control system in the modal domain is presented. The formulation is applied to a simply supported beam with SISO feedforward control. Radiation efficiency, far-field sound radiated power and mean-square surface velocity are extensively studied. The results show that the control scheme proposed here is very efficient in reducing sound radiation at low frequencies.
Electroacoustical measurements of silicon microphones on wafer scale
Authors: Pedersen Michael , Schellin Ralf , Olthuis Wouter , Bergveld Piet
Published: July 2002

A new method for the electroacoustic characterization of small-sized silicon microphones is described. Using closed-field acoustical measurements, it is demonstrated how a precise device characterization can be carried out directly on wafer-scale, thereby eliminating the need to separate and mount each microphone. The performance of the setup is illustrated by measurements on piezoelectric and condenser microphones. Accurate measurements of the frequency response can be performed between 100 Hz and 15 kHz. The determination of the total harmonic distortion of the condenser microphones has been done for SPL (SPL=sound pressure level) from 95 to 125 dB and of the piezoelectric microphones for SPL from 110 to 127 dB, respectively. Furthermore, the A-weighted noise voltage of the microphones can be measured easily. Regarding size, 2- to 4-in. wafers may be used and the minimum measurable chip area is about 1.5 mm2. An almost complete characterization of a microphone, including the different measurements mentioned above, can be carried out within a few minutes. By measuring several microphones on several wafers, important information, such as yield and reproducibility, can be obtained. Additionally, statistical calculations on sensitivity, equivalent noise level, etc. can be performed.
Relating change in signal-to-noise ratio to array gain for microphone arrays used in rooms
Authors: Kates James M.
Published: July 2002

Microphone arrays have proven effective in improving speech intelligibility in noise for the hearing impaired. Two different acoustic performance metrics have been proposed for evaluating the performance of microphone arrays in reverberant rooms. The signal-to-noise ratio (SNR) metric uses the improvement in SNR at the microphone output relative to the microphone input, and includes the reverberant speech as part of the desired speech signal. The array-gain metric, on the other hand, ignores the reverberant speech and measures the degree to which the noise in the room has been suppressed. An approximate relationship between these two metrics is derived so that results using one metric can be compared to results using the other even when the signal and noise correlation matrices are not available.
Changes in evoked otoacoustic emissions in the guinea pig after pure-tone acoustic overstimulation
Authors: Ueda Hiromi , Tsuge Hayato , Hattori Taku
Published: July 2002

To test if click-evoked otoacoustic emissions (CEOAEs) have frequency specificity, continuous changes in CEOAEs (especially frequency components of the CEOAE power spectrum) after pure-tone exposure in guinea pigs were examined. Pure-tone stimuli (0.5 kHz, 120 dB SPL; 2 kHz, 115 dB SPL; 4 kHz, 110 dB SPL) were given in a closed system for 3 min. After exposure, the frequency components in the CEOAE power spectrum decreased maximally at one-half octave or more above the overstimulation frequency. They partially recovered 2 h after exposure. The time course of compound action potential (CAP) thresholds after exposure was similar to that of the frequency components of the CEOAE power spectrum. It was concluded that some local damage caused by outer hair-cell dysfunction in the guinea pig cochlea can be detected by measuring shifts in frequency components in the CEOAE power spectrum.
Double-sum technique for performing a Fourier transformation
Authors: Maidanik G. , Becker K. J.
Published: July 2002

Structural acoustics often utilizes Fourier transformation to either reveal a phenomenon that is more directly recognized in one domain than in its Fourier conjugate domain or to employ complementarity in order to decipher a phenomenon. In this paper, a novel computational technique is introduced. This technique advantageously performs this transformation in situations in which specific spatial scales govern aliased factors in the integrand of a Fourier transformation. The technique can factorially save computational steps over corresponding computations that employ discrete Fourier transform procedures.
On the onset of transient cavitation in gassy liquids
Authors: Gaete-Garretón L. , Vargas-Hernández Y. , Vargas-Herrera R. , Gallego-Juárez J. A. , Montoya-Vitini F.
Published: July 2002

This paper deals with a numerical and experimental study of ultrasound induced cavitation. On the basis of a computational analysis of Gilmore’s equation for the individual bubble dynamics, a slight decrease in the pressure radiated by a single bubble immediately before reaching the transient cavitation regime is predicted. Experiments presented in this paper confirm this observation. Therefore, a new method to detect the inception of transient cavitation is proposed. The numerical analysis of a single bubble behavior, carried out for the different bubble sizes, suggests that two distinct “types” of transient cavitation may occur in a cavitation field in connection with the relative number of bubbles involved in the process. The experiments seem to confirm the theoretical hypothesis. The experimental work consisted mainly of insonifying distilled water, with a gas content of about 75% of saturation, at 20 kHz and analyzing the resulting acoustic emissions.
Analytical expressions for high-frequency acoustic fluctuations from suspended particles in the ocean
Authors: Thuraisingham R. A.
Published: July 2002

Simple analytical expressions for amplitude and phase fluctuations of high-frequency sound from suspended particles in the ocean are derived. The fluctuations depend on the wave number, path length, particle radius, the relative volume density of scatterers (σ), and the ratio of sound speed in the medium to that of the scatterer. The expressions are valid in the Rytov region.
A targeting-and-extracting technique to enhance hearing in the presence of competing speech
Authors: Liu Chen , Rosenhouse Judith , Sideman Samuel
Published: July 2002

A targeting-and-extracting procedure of speech enhancement for hearing aids in the presence of background noise, especially competing speech, is proposed. The procedure is composed of two steps: targeting by a fixed (or deterministic) beamforming array, followed by a post-targeting extracting step. Emphasis is placed on the extracting step, which performs noise cancellation based on the acoustic difference between the desired speech and interfering speech. Either comb filtering or attenuation is applied to the signal in accordance with the current voiced/unvoiced/silence state of the desired signal. The comb filter design is based on the fundamental pitch frequency of the desired speech. Algorithms for deciding the voiced/unvoiced/silence state and determining the fundamental frequency are developed. The performance of the system is evaluated through computer simulation. The simulation results indicate significant noise cancellation and intelligibility improvement.
Acoustic scattering by a pair of spheres: Addenda and corrigenda
Authors: Gaunaurd Guillermo C. , Huang Hanson , Strifors Hans C.
Published: July 2002

Our earlier work on acoustic scattering by multiple bodies is being updated by summarizing recent extensions in several new publications. Two figures that were not entirely correct in one of our earlier papers have been replotted and pertinent new physical interpretations have been added.
Comments on “Flexural wave reduction using a compliant tube baffle” [J. Acoust. Soc. Am. 99(2), 691–699 (1996)] and “Signal pressure received by a hydrophone placed on a plate backed by a compliant baffle” [J. Acoust. Soc. Am. 89(2), 559–564 (1991)]
Authors: Radlinski Ronald P. , Ko Sung H.
Published: July 2002

The cited formulations for studying the baffling of flexural waves by a compliant tube grating [S. H. Ko, J. Acoust. Soc. Am. 99, 691–699 (1996)] and for determining the acoustic receive sensitivity of a hydrophone placed near a plate backed by a compliant tube grating [S. H. Ko and H. H. Schloemer, J. Acoust. Soc. Am. 89, 559–564 (1991)] are dependent on the validity of the lumped-fluid parameter approximations developed by Junger [M. C. Junger, J. Acoust. Soc. Am. 78, 1010–1012 (1985)] for a grating of closely spaced compliant tubes between two semi-infinite fluid half-spaces. If the fluid between the plate and the grating is great enough to minimize their interaction, the incorporation of the effective layer parameters developed by Junger should be reasonably valid. Unfortunately, the sample calculations in Ko (Ref. 4) and Ko and Schloemer (Ref. 5) have been made for the limiting case of the compliant tube grating in direct contact with the plates where the use of Junger’s approximations is inappropriate.
Spectral statistics in damped systems: Diffuse field decay curvature for materials characterization
Authors: Burkhardt John
Published: July 2002

A new nondestructive technique is proposed which exploits the unique decay characteristics of diffuse fields in nonproportionally damped systems. A power-law decay model is derived and advanced as the basis for the inverse estimation of both the strength and spatial extent of the dissipative region in nonproportionally damped systems. In materials where mechanical damage results in increased internal friction, a common effect in many engineering metals, this technique is proposed as a nondestructive technique for characterizing such damage. The results of numerical experiments on nonproportionally damped acoustic systems are presented which support the proposed technique.
A method for acoustic scattering by slender bodies. II. Comparison with laboratory measurements
Authors: Ding Li , Ye Zhen
Published: July 2002

This paper describes a comparison between a sound scattering model for slender bodies proposed in Ye et al. [J. Acoust. Soc. Am. 102, 1964–1976 (1997)], and laboratory measurements of forward and bistatic scattering by individual fish [Ding, J. Acoust. Soc. Am. 101, 3398–3404 (1997)]. A prolate spheroid target made of styrofoam is also measured to help verify the model, and it is found that the model results agree reasonably well with the measurements of the styrofoam target. Scattering of fish is assumed to be primarily due to fish flesh and swimbladder, which are modeled as liquid filled and gas filled, respectively. An asymmetric prolate spheroid is used to approximate the geometry of both fish body and swimbladder. It is shown in the modeling that fish body (flesh) is more important in determining the forward scattering at the frequency of interest (38 kHz), while in the case of bistatic scattering, swimbladder is still dominant. The model appears able to produce results in good agreement with the measurements of bistatic scattering, for incident angles within ±40°. For forward scattering, the model results of fish body follow well the general trends of the data for one side of incident angles, but for the other side, do not show as large variability as the data, suggesting more complex structures involved. When the scattering by swimbladder is added coherently to that of fish body, the total scattering is stronger than the data. Therefore it remains an open question how to combine contributions from fish body and swimbladder when their scattering strengths are not significantly different.
A phase-inverting parabolic concentrator for the generation of negative waves in water
Authors: Carnell M. T. , Barrington S. J. , Emmony D. C.
Published: July 2002

A method of generating very strong focused negative pressure fields in water for cavitation studies from shock waves produced by an electromagnetic transducer is described. By using a reflecting concentrator with a phase-inverting central element, focal pressures of around −16 MPa from a +5-MPa source have been measured. The combination of an electromagnetic transducer and a phase-inverting parabolic concentrator provides a reliable and reproducible source of cavitation bubbles for study. A qualitative study of the cavitation field produced by the device, using a laser schlieren technique, is presented.
Acoustic field prediction for a single planar continuous-wave source using an equivalent phased array method
Authors: Fan Xiaobing , Moros Eduardo G. , Straube William L.
Published: July 2002

Phased array theory is combined with the Rayleigh–Sommerfeld diffraction integral to predict measured acoustic fields generated by a single-source ultrasonic transducer. The idea is to treat a single-source as a “phased array,” which is composed of many small elements. The goal is to find the excitation source for the phased array, that is, the amplitude and phase for each array element, which produces an acoustic field similar to the experimentally measured field generated by the single-source transducer. A pressure field measured at a given plane parallel and close to the face of the transducer in degased water was used to calculate the excitation source of the equivalent phased array using an inverse technique. The excitation source of the equivalent phased array was then used to calculate the acoustic field from this measurement plane to the far field. It was demonstrated that this phased array approach accurately predicted the location of major grating lobes and the general distributions of the near and far pressure fields for four different transducers. This equivalent phased array method (EPAM) used to model a single-source transducer should be useful in both diagnostic and therapeutic ultrasound applications.
A correction and explanation on: “Acoustic wave propagation through porous media revisited” [J. Acoust. Soc. Am. 100, 2949–2959 (1996)]
Authors: Geerits Tim W.
Published: July 2002

The author clarifies and corrects his recent article.
Microstructured elastomeric electromechanical film transducer
Authors: Whitehead Lorne A. , Bolleman Brent J.
Published: July 2002

A new electrostatic film transducer is described. This transducer uses a flexible sheet of elastomeric microstructures to achieve a wide range of internal impedance and driving pressure. A simple single degree of freedom model is used to predict the performance of the device and the predictions have been confirmed by measurements made on a prototype device.
An iterative solver of the Helmholtz integral equation for high-frequency acoustic scattering
Authors: Makarov S. N. , Ochmann M.
Published: July 2002

High-frequency scattering from convex and non-convex bodies is studied using an iterative algorithm. The key point of the method is a self-adjoint formulation of the Helmholtz integral equation, which ensures the convergence of the iteration process toward the true solution. For all investigated structures with different surface impedances fast convergence could be observed. The number of surface elements of the scatterer varies from about 6000 to 60 000 and the calculations are performed in the high-frequency range with Helmholtz numbers ka between 20 and 63. Even for a scattering structure with nearly 60 000 boundary elements, all computations could be carried out on a regular personal computer.
Early decay times in the Christchurch and Wellington concert halls, New Zealand
Authors: Barron M.
Published: July 2002

The concert halls in Christchurch Town Hall and the Michael Fowler Centre, Wellington, New Zealand, have large suspended reflecting surfaces which provide early lateral reflections to listeners. One objective outcome of this is that measured early decay time (EDT) values are shorter than the reverberation time. EDT values for these two halls published in the book, Auditorium Acoustics and Architectural Design (Spon/Chapman & Hall, London, 1993) are now known to be significantly in error, due to a software fault in the signal analysis program used. Corrected diagrams including the EDT are presented as well as a brief discussion of sound decay in these halls.
Air transducers with high acoustic impedance
Authors: Lynnworth Lawrence C.
Published: July 2002

High-Z air transducers evolved from several industrial transducers. These predecessors include (a) acoustic emission and angle-beam NDT contact transducers; (b) flowmeter transducers for high-pressure methane, hot refinery gases, and corrosive flare gases; and (c) transducer arrays for monitoring hot corrosive gases flowing at Mach 0.1 in smokestacks of φ3–13 m. This peculiar ancestry accounts for their unusual high-acoustic-impedance construction. By not employing low-Z air-backed radiating membranes, transducer bandwidth, response time, and sensitivity are sacrificed. The solid, robust construction, however, offers some compensating features: tolerance to wide ranges in pressure and temperature, including rapid rates of change (thermal shock, depressurization); corrosion resistance; operable with standard lab equipment, without bias voltage; mounting options where the transducer forms part of the pressure boundary, or where it is outside the pressure boundary. Clamp-on air flow applications at one bar include small wind tunnels and plastic pipes. Acoustically isolated pairs measure secondary flow components (crossflow, circulation) in a plane perpendicular to the pipe axis. Flow applications include gases such as air, mild steam (pending) or other hot, pressurized, or corrosive fluids. Air-coupled measurements of transmission characteristics of wood or other low-density solids, and air-ranging, are readily demonstrated with the low-Z transducers.
Recent developments in air-coupled ultrasonic capacitive transducers for NDE
Authors: McIntyre Craig S. , Hutchins David A. , Schindel David W.
Published: July 2002

A new design of an air-coupled capacitive ultrasonic transducer has been developed that could have potential for use in NDE experiments, particularly when the pulse-echo method is employed. The design is based on a standard capacitive transducer, except the newly developed device has two concentric, backplate elements with a common membrane. Each of the elements is electrically isolated from the other, allowing one to be used as a source of ultrasound, while the other is used as a detector. This yields a device containing both a source and receiver of ultrasound within the same structure. Experiments have shown that the device performance depends on which of the elements is selected to be source and receiver, size of the bias voltage employed, surface of the backplates, and membrane material utilized. Initial studies have shown that the device is capable of detecting the front face echo from various material samples, and these results are contained within this paper. There has also been some investigation of the signal quality when capacitive devices have been placed within an enviroment containing a range of pressures above standard atmospheric pressure. Applications of this work include measurements in high-pressure gas pipelines.
Jet wave amplification in organ pipes
Authors: Yoshikawa Shigeru
Published: July 2002

The amplification factor of an air jet waving over the mouth is estimated from flow visualization of the smoked jet, where the velocity ranges from 7–33 m/s, the Reynolds number from 1000–5000, and the sounding frequency from 130–580 Hz. The jet length is 15.8 and 10.2 mm in two models, while the jet thickness is 2.2 mm in both. The estimation is carried out by comparing the visualized envelope of jet waves with a simplified theoretical one. The envelope is visualized by the OR summation of the digitally memorized frames showing the instantaneous deflection taken with a speed of 1440 frames per second. Furthermore, the strength of mouth field defined as the acoustic displacement amplitude is derived from the envelope-based estimation. A hot-wire anemometer is then applied to measure this mouth-field strength, whose value shows a good agreement with the estimated result. The amplification factor of organ jets was estimated as 0.26 to 0.18 (1/mm); the mouth-field strength as 0.5 to 1.5 mm. A nondimensionalized representation of the relation between the amplification factor and the blowing velocity in our organ-pipe jets roughly agrees with the theoretical curve based on the linearized spatial analysis of jet instability.
Theoretical and experimental investigation of the air-driven free reed
Authors: Cottingham James P.
Published: July 2002

The free reed is the excitation mechanism for several families of instruments, including the reed organ and harmonium, the harmonica, the accordion and concertina, and the Asian free reed mouth organs. While most studies of reed behavior have concentrated on reeds which are either inward-striking (closing) and outward-striking (opening), free reeds do not fit neatly into either category and can exhibit behavior characteristic of either opening or closing reeds, depending on certain details of the reed configuration. Some characteristics of free reed behavior, in particular the relation between frequency and blowing pressure, have been modeled by adapting Fletcher’s analysis of musical instruments driven by a reed mechanism [N. H. Fletcher, Acustica 43, 63–72 (1979)]. In addition, a variety of measurements of reed motion have been made, including experimental determination of measurements of reed position and phase using proximity sensors. These are compared with observations of the near-field sound as well as with predictions based on theoretical considerations.
Studies on a new type of silencer for air ducts
Authors: Shenoda Fathy B. , Haroun Reda N.
Published: July 2002

The research work deals with a study of a specific type of silencer previously designed and tested by Shenoda. It consists of a rectangular duct, which is treated at its side walls with a gradually variable flow resistance. It was realized by increasing the perforated area along the duct wall combined with an homogeneous sound absorbing material. Based on the assumptions that only plane waves propagate in the duct, ignoring the effect of the mean flow velocity (very low) and applying linear acoustic equations, the sound propagation in such a silencer was studied. Therefore the wave impedance, the sound reflection coefficient at the input of the silencer, and the transmission loss introduced by it were calculated, measured, and compared with a silencer of comparable dimensions which is treated with a constant flow resistance along its length. To optimize the design different configurations were theoretically studied, computed, and compared. An important result: The silencer performance depends on a unique design parameter, namely, the silencer characteristic area. The methods of realizing a variable wall flow resistance were introduced. The effect of using different kinds of sound absorbing materials and changing the graduality of the variable flow resistance were measured.