Volume 109, Issue 6, June 2001
- acoustical news—usa
- acoustical news—international
- reports of related meetings
- book reviews
- reviews of acoustical patents
- general linear acoustics 
- nonlinear acoustics 
- aeroacoustics, atmospheric sound 
- underwater sound 
- ultrasonics, quantum acoustics, and physical effects of sound 
- transduction 
- structural acoustics and vibration 
- noise: its effects and control 
- acoustical measurements and instrumentation 
- acoustic signal processing 
- physiological acoustics 
- psychological acoustics 
- speech production 
- speech perception 
- speech processing and communication systems 
- music and musical instruments 
- bioacoustics 
- letters to the editor
- letters to the editor
Index of content:
- REPORTS OF RELATED MEETINGS
109(2001); http://dx.doi.org/10.1121/1.4776777View Description Hide Description
109(2001); http://dx.doi.org/10.1121/1.4776778View Description Hide Description
- REVIEWS OF ACOUSTICAL PATENTS
109(2001); http://dx.doi.org/10.1121/1.4736959View Description Hide Description
The purpose of these acoustical patent reviews is to provide enough information for a Journal reader to decide whether to seek more information from the patent itself. Any opinions expressed here are those of the reviewers as individuals and are not legal opinions. Printed copies of United States Patents may be ordered at $3.00 each from the Commissioner of Patents and Trademarks, Washington, DC 20231. Patents are available via the Internet at http://www.uspto.gov.
109(2001); http://dx.doi.org/10.1121/1.1367246View Description Hide Description
A tutorial exposition is given of cavity excitations and it is shown that relatively simple analytical solutions for the excitation of acoustic fields in cavities with lossy walls can be obtained for a broad class of such cavities. The standard analytic procedure whereby one expresses the acoustic field as a sum over the eigenmodes of the cavity is reviewed and its limitations are pointed out. An alternate procedure is to seek to make use of Green’s functions depending on a single coordinate and to not express such Green’s functions as sums over eigenfunctions. Instead, one expresses the Green’s function as a closed form function that has a discontinuous slope at the value of the coordinate corresponding to the source location. Although the class of cavities for which this approach is possible is limited, it is sufficiently broad to be of intrinsic interest and the results may be helpful to those seeking benchmark solutions and analytic insight. Displayed examples are for cavities whose shapes are spheres and cylinders, with interior monopole, dipole, line, and distributed sources. The formulation yields simple expressions for the total power absorbed by the cavity walls.
- GENERAL LINEAR ACOUSTICS 
A staggered-grid finite-difference method with perfectly matched layers for poroelastic wave equations109(2001); http://dx.doi.org/10.1121/1.1369783View Description Hide Description
A particle velocity-strain, finite-difference (FD) method with a perfectly matched layer (PML) absorbing boundary condition is developed for the simulation of elastic wave propagation in multidimensional heterogeneous poroelastic media. Instead of the widely used second-order differential equations, a first-order hyperbolic leap-frog system is obtained from Biot’s equations. To achieve a high accuracy, the first-order hyperbolic system is discretized on a staggered grid both in time and space. The perfectly matched layer is used at the computational edge to absorb the outgoing waves. The performance of the PML is investigated by calculating the reflection from the boundary. The numerical method is validated by analytical solutions. This FD algorithm is used to study the interaction of elastic waves with a buried land mine. Three cases are simulated for a mine-like object buried in “sand,” in purely dry “sand” and in “mud.” The results show that the wave responses are significantly different in these cases. The target can be detected by using acoustic measurements after processing.
109(2001); http://dx.doi.org/10.1121/1.1373448View Description Hide Description
Pulse propagation in a weakly and randomly inhomogeneous medium is studied using a time-domain progressive wave equation. An eikonal-like approximated solution to the wave equation derived from the path integral representation is used to obtain the time-dependent statistics of pulses propagating through this random medium. This approach yields both a simple way of producing simulations of time series as well as their statistical properties.
109(2001); http://dx.doi.org/10.1121/1.1369101View Description Hide Description
Classical fisheries acoustics techniques are useless in the presence of multiple scattering or reflecting boundaries. A general technique is developed that provides the number and the scattering strength of scatterers in motion placed inside a highly reflecting cavity. This approach is based on multiple scatteringtheory. The idea is to measure the average effect of the scatterers on the acoustic echoes of the cavityinterfaces. This leads to the measure of the scattering mean free path, a typical length that characterizes the scattering strength of the cloud of scatterers. Numerical results are shown to agree with a simple theoretical analysis. Experiments are performed with fish in a tank at two different scales: ultrasonic frequency (400 kHz) in a 1.4-1 beaker with 1-cm-long fish as well as fisheries acoustics frequency (12.8 kHz) in a 30-m3 tank with 35-cm-long fish. These results have interesting applications to fish target strength measurement and fish counting in aquaculture.
109(2001); http://dx.doi.org/10.1121/1.1369784View Description Hide Description
An analysis of the reflectance of sonic band-gap crystals consisting of square arrays of rigid cylinders in air is presented. The standing wave formed in front of the structures is studied both experimentally and theoretically. Experiments have been performed with a mobile robotized microphone that obtains pressure maps on the plane perpendicular to the axes of the cylinders. Enhancements of the standing wave ratio (SWR) are observed in frequency regions where attenuation bands appear in zero-order transmission experiments. Also, the SWR presents oscillations that can be related to the finite dimension of the structure (Fabry–Perot effect). Both features are well described by calculations based on a double-scattering approach.
109(2001); http://dx.doi.org/10.1121/1.1369102View Description Hide Description
In previous work [C. Feuillade, J. Acoust. Soc. Am. 98, 1178–1190 (1995)] a coupled oscillator formalism was introduced for describing collective resonances, scattering, and superresonances, of multiple gas bubbles in a fluid. Subsequently, time-domain investigations of the impulse response of coupled systems have disclosed the exact conditions which determine whether the ensemble scattering behavior should be described using: either (a), a multiple scattering; or (b), a self-consistent methodology. The determining factor is the Q of the individual scatterers, and their typical spatial separations in the medium. For highly damped or sparse systems, e.g., scattering from loose schools of swimbladder fish, or from a gassy seabed containing entrained bubbles, the multiple scatter counting approach should be applicable. For more strongly coupled systems, e.g., a dense cloud of resonating bubbles in the water column, energy exchange may be due primarily to radiative cycling rather than scattering, in which case a self-consistent approach is indicated. The result has implications for both volume and bottom scattering applications.
109(2001); http://dx.doi.org/10.1121/1.1368404View Description Hide Description
We show that the time reversal operator for a planar time reversal mirror (TRM) can have up to four distinct eigenvalues with a small spherical acoustic scatterer. Each eigenstate represents a resonance between the TRM and an induced scattering moment of the sphere. Their amplitude distributions on the TRM are orthogonal superpositions of the radiation patterns from a monopole and up to three orthogonal dipoles. The induced monopole moment is associated with the compressibility contrast between the sphere and the medium, while the dipole moments are associated with density contrast. The number of eigenstates is related to the number of orthogonal orientations of each induced multipole. For hard spheres (glass, metals) the contribution of the monopole moment to the eigenvalues is much greater than that of the dipole moments, leading to a single dominant eigenvalue. The other eigenvalues are much smaller, making it unlikely multiple eigenvalues could have been observed in previous experiments using hard materials. However, for soft materials such as wood, plastic, or air bubbles the eigenvalues are comparable in magnitude and should be observable. The presence of multiple eigenstates breaks the one-to-one correspondence between eigenstates and distinguishable scatterers discussed previously by Prada and Fink [Wave Motion 20, 151–163 (1994)]. However, eigenfunctions from separate scatterers would have different phases for their eigenfunctions, potentially restoring the ability to distinguish separate scatterers. Since relative magnitudes of the eigenvalues for a single scatterer are governed by the ratio of the compressibility contrast to the density contrast, measurement of the eigenvalue spectrum would provide information on the composition of the scatterer.
109(2001); http://dx.doi.org/10.1121/1.1371765View Description Hide Description
An explicit solution of the surface displacements due to a line force or a line dislocation within an anisotropic half-space is presented. The surface displacements are derived from the solution corresponding to a suddenly applied surface line force using the reciprocal theorem. The solution is in a closed form for isotropic media. For anisotropic solids, only an eigenvalue problem needs to be solved numerically for a given time and position to calculate the surface response. Numerical results are given for silicon.
109(2001); http://dx.doi.org/10.1121/1.1367248View Description Hide Description
Formulation for calculating forward propagation and reflection in a 3D elastic structure based on the complex-screen method is given in this paper. The calculation of reflections is formulated based on the local Born approximation. When using a small angle approximation, the backscattering operator reduces to a screen operator which is similar to the forward screen propagator. Combining the forward propagator and backscattering operator together, the new method can properly handle the multiple forward scattering and single backscattering in a 3D heterogeneous model. Using a dual-domain technique, the new method is highly efficient in CPU time and memory savings. For models where reverberation and resonance scattering can be neglected, this method provides a fast and accurate algorithm. Synthetic seismograms for two-dimensional elastic models are calculated with this method and compared with those generated by the finite-difference method. The results show that the method works well for small to medium scattering angles and medium velocity contrasts.
109(2001); http://dx.doi.org/10.1121/1.1372914View Description Hide Description
Measurements of the ultrasonic modal density of a disordered elastic frame, a 20 pore-per-inch open-celled aluminumfoam, are reported. While the material is dissipative, with a Q only around 700, sufficiently careful signal processing has allowed reliable counts of the modes up through a few hundred, corresponding to wavelengths comparable to the strut lengths. The modal density is found to be essentially constant over this range, and to bear no resemblance to theoretical estimates based on long-wavelength effective moduli.
- NONLINEAR ACOUSTICS 
109(2001); http://dx.doi.org/10.1121/1.1369096View Description Hide Description
The theoretical investigation of mechanisms of the acoustic nonlinearity(elastic and inelastic) of cracks partially filled with an ideal and viscousliquid and associated with the nonlinear dependence of the capillary and viscouspressure in the liquid on the distance between the crack surfaces and the velocity of the change of this distance is proposed. The nonlinear (in cubic approximation) equations of the state of these cracks is obtained, and its parameters are defined. It is shown that the presence of the viscousliquid may lead to the considerable increase of the acoustic nonlinearity of such cracks in comparison with cracks filled with the ideal liquid.