Volume 103, Issue 2, February 1998
- acoustical news—usa
- acoustical news—international
- reports of related meetings
- reviews of acoustical patents
- selected research articles 
- general linear acoustics 
- underwater sound 
- ultrasonics, quantum acoustics, and physical effects of sound 
- structural acoustics and vibration 
- noise: its effects and control 
- acoustical measurements and instrumentation 
- physiological acoustics 
- psychological acoustics 
- speech production 
- speech perception 
- music and musical instruments 
- bioacoustics 
- letters to the editor
- technical notes and research briefs
Index of content:
- ACOUSTICAL NEWS—USA
- ACOUSTICAL NEWS—INTERNATIONAL
- REPORTS OF RELATED MEETINGS
- REVIEWS OF ACOUSTICAL PATENTS
103(1998); http://dx.doi.org/10.1121/1.423117View 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.
- SELECTED RESEARCH ARTICLES 
103(1998); http://dx.doi.org/10.1121/1.423235View Description Hide Description
Ultrasonic waves reflected from the front and back surfaces of a thin layer are often not separated in the time domain, and interfere. The spectrum of the resulting interference signal depends on (a) the thickness of the layer and the elastic moduli and density of the layer and the surrounding material (substrates), and (b) properties of the layer/substrate interface which can be described in terms of the interfacial stiffness. In this paper the effect of interfacial stiffness is isolated by considering the ultrasonic wave interaction with a solid layer compressed between two substrates of the same material. Since the layer and the substrate have identical properties the effect of impedance difference on the layer reflection vanishes. An aluminum system is selected for the experiment; the contacting surfaces are roughened and varying pressure is applied to model imperfect interface changes. It is shown both theoretically and experimentally that the contact pressure increase results in increase of the interfacial stiffness and spectral minima shift to higher frequency. A simple analytical expression relating the reflection minimum position to the interfacial stiffness is derived and shows good agreement with experimental results. It is shown that in the high-interfacial-stiffness limit the resonance minima positions are given by the condition In the limit of low interfacial stiffness the first minimum shifts to zero and higher order resonances are given by Since the resonance minima measurements can be done with high precision it is proposed to use the frequency minimum shift for determination of interfacial stiffness and, consequently, the quality of the interfacial contact.
Development of a new standard laboratory protocol for estimating the field attenuation of hearing protection devices. Part III. The validity of using subject-fit data103(1998); http://dx.doi.org/10.1121/1.423236View Description Hide Description
The mandate of ASA Working Group S12/WG11 has been to develop “laboratory and/or field procedure(s) that yield useful estimates of field performance” of hearing protection devices (HPDs). A real-ear attenuation at threshold procedure was selected, devised, tested via an interlaboratory study, and incorporated into a draft standard that was approved in 1997 [J. D. Royster et al., “Development of a new standard laboratory protocol for estimating the field attenuation of hearing protection devices. Part I. Research of Working Group 11, Accredited Standards Committee S12, Noise,” J. Acoust. Soc. Am. 99, 1506–1526 (1996); ANSI S12.6-1997, “American National Standard Methods for Measuring Real-Ear Attenuation of Hearing Protectors” (American National Standards Institute, New York, 1997)]. The real-world estimation procedure utilizes a subject-fit methodology with listeners who are audiometrically proficient, but inexperienced in the use of HPDs. A key factor in the decision to utilize the subject-fit method was an evaluation of the representativeness of the laboratory data vis-à-vis attenuation values achieved by workers in practice. Twenty-two field studies were reviewed to develop a data base for comparison purposes. Results indicated that laboratory subject-fit attenuation values were typically equivalent to or greater than the field attenuation values, and yielded a better estimate of those values than did experimenter-fit or experimenter-supervised fit types of results. Recent data which are discussed in the paper, but which were not available at the time of the original analyses, confirm the findings.
- GENERAL LINEAR ACOUSTICS 
Acoustic scattering on an elastic plate described by the Timoshenko model: Contact conditions and uniqueness of the solution103(1998); http://dx.doi.org/10.1121/1.421195View Description Hide Description
It is shown that the known solution of the acoustic scattering problem on a supported elastic plate, described by the Timoshenko model, should be corrected. The general formulation of the contact conditions that imply the reciprocity principle is given. Sommerfeld’s formula and the “optical” theorem for the model are formulated. They lead to the uniqueness of the solution. The numerical comparison of the effective cross section of scattering from supported elastic plate described by the Kirchhoff and by the Timoshenko models is presented.
103(1998); http://dx.doi.org/10.1121/1.421237View Description Hide Description
It was shown by Purcell [J. Acoust. Soc. Am. 100, 2919–2936 (1996)] that the Rayleigh equations in the Fourier domain for the reflection coefficients for scattering of a plane wave from a pressure-release sinusoid are valid if the maximum slope of the sinusoid This current work finds the corresponding constraint sufficient for the validity of Rayleigh’s equations for a more general periodic surface consisting of a finite sum of sinusoids. The mathematical basis of the derivation of the Rayleigh equations from the Helmholtz integral formula is a Fourier series given by Oberhettinger. Unlike the single sinusoid case developed by Purcell (referenced above), the analysis of the general periodic surface given here requires an analytic continuation argument. In addition, a set of (infinite linear) equations of the “second kind” is derived for the reflection coefficients for the general periodic surface. This guarantees that the truncation solutions for the reflection coefficients converge and are unique. The matrix elements involved in these equations of the second kind require the numerical evaluation of a finite integral (a generalization of Bessel’s integral for the integer index Bessel functions) and all calculations required can be performed by desktop computing.
103(1998); http://dx.doi.org/10.1121/1.421196View Description Hide Description
The dispersion equation for Love wave propagation in a layer lying over a half-space is derived. Both media are assumed to be transversely isotropic fluid-saturated poroelastic solids with principal axes perpendicular to the surface. The analysis is based on the Biot’s theory. The dissipation due to fluid viscosity is considered and therefore the dispersion equation is complex and intractable analytically. An iterative procedure is developed to solve this equation. Two situations are discussed in detail: (i) an elastic layer overlying a poroelastic half-space and (ii) a poroelastic layer lying over an elastic half-space. Dispersion curves and attenuation curves of Love waves are plotted for these two cases. In addition, the upper and lower bounds of Love wave speeds are also explored.
103(1998); http://dx.doi.org/10.1121/1.421230View Description Hide Description
This paper presents a numerical program for the simulation of elastic wave propagation and scattering in three-dimensional (3-D) cylindrical coordinates based on the first-order velocity-stress finite-difference scheme on staggered grids. Both Liao’s and Lindman’s absorbing boundary conditions are implemented for the exterior boundaries to efficiently truncate the computation domain for elongated 3-D well logging problems. Symmetric and anti-symmetric boundaries in azimuthal and axial directions are also implemented in the code to further reduce the size of the problem. Included for the first time with this code are very large and complex geometrical structures such as the whole slotted sleeve housing of a sonic well-logging tool which typically involves hundreds of millions of unknowns. The calculation for such a large problem only takes a couple of days on a four-processor SGI Power Challenge machine. Different types of slotted sleeve models are studied for sonic logging tools. Simulation results show that different slotted sleeves vary widely in delaying and attenuating the pipe waves which travel along the tool housing. A new slotted sleeve structure with three horizontal slot sections for every vertical slot period is proposed for better performance. A dipole source is found to produce much cleaner waveforms than a monopole source.
103(1998); http://dx.doi.org/10.1121/1.421197View Description Hide Description
A fast, efficient algorithm for computing acoustic fields scattered by inhomogeneous objects in an otherwise homogeneous space is presented. The algorithm, called the Recursive Green’s Function Method (RGFM), constructs the domain Green’s function by recursively combining known Green’s functions from smaller subdomains. The fields on the scatterer surface are then computed using a boundary integral formulation. Proper implementation of the RGFM results in a storage requirement of and computational costs of and for two- and three-dimensional problems, respectively, where is the total number of discrete points in the inhomogeneous region. Results are compared with those obtained from exact solutions to show the accuracy of the method.
103(1998); http://dx.doi.org/10.1121/1.421231View Description Hide Description
The problem of determining the field scattered by a cluster of scatterers when they are insonified by a known acoustical field is addressed. The problem is formulated by using the -matrix method and the resulting system of linear equations is solved by using the multilevel fast multipole algorithm (MLFMA) and the fast multipole method–fast Fourier transform (FMMFFT) method, and the efficiency of the two methods is compared. It was observed that, in general, the MLFMA performs better than the FMMFFT algorithm. However, when the scatterers are distributed uniformly on a rectangular grid, the FMMFFT algorithm performs as good as the MLFMA. The accuracy of the methods is evaluated by modeling a spherical scatterer as composed of many small spheres.
103(1998); http://dx.doi.org/10.1121/1.421198View Description Hide Description
The parabolic equation technique is used to solve the Helmholtz equation in the presence of scatterers of arbitrary shape, in two and three dimensions. The scattered field is computed directly, using non-homogeneous boundary conditions on the scattering object to represent the incident field. Effectively this decouples the PE paraxial direction from the direction of incidence. For convex objects the whole range of scattering angles can be covered with a small number of narrow-angle calculations. Finite-difference implementations involve tridiagonal matrices in two dimensions and more general sparse matrices in three dimensions. The resulting codes can be used to solve scattering problems for objects ranging in size from a few wavelengths to hundreds of wavelengths. The method has been tested against analytical solutions for soft and rigid circular cylinders in 2D and soft and rigid spheres in 3D, showing good agreement at all scattering angles.
103(1998); http://dx.doi.org/10.1121/1.421238View Description Hide Description
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 between 20 and 63. Even for a scatteringstructure with nearly 60 000 boundary elements, all computations could be carried out on a regular personal computer.
103(1998); http://dx.doi.org/10.1121/1.421239View Description Hide Description
This paper presents a probabilistic study of the effects of structural irregularity on wave propagation along an infinite 1-D chain. A general integral equation method based on Markov chain theory is used to determine the phase probability density function (pdf) at the scatterers distributed irregularly along the chain. The scatterers could be atoms in a one-dimensional crystal, or ribs on a flat plate or membrane. The integral equation derived for the phase pdf is simplified considerably when the scatterers are distributed completely randomly or quasi-periodically. In these cases, the integral equations may be asymptotically solved for the phase density functions in the limit of weak or strong scattering; the localization factors are then obtained. The present approach is quite general and is directly applicable to any disordered one-dimensional system consisting of identical scatterers that are arranged according to a probability distribution function. The validity of the present asymptotic solutions is examined and verified by comparing against the existing analytical solutions for simple atomic or mechanical disordered systems.
103(1998); http://dx.doi.org/10.1121/1.421199View Description Hide Description
The pure shear problem is one of relative mathematical simplicity and includes the essential physics common to more complicated cases, where multiple and coupled deformations occur. In this sense, the analysis of torsional waves serves as a pilot problem for investigating the influence of anisotropy and/or anelasticity on solution behavior. We obtain the kinematic and dynamic properties of torsional axially symmetric harmonic waves propagating in an infinitely long circular cylinder. The medium is transversely isotropic and dissipative, with its symmetry axis coincident with the axial axis of the cylinder. For an elastic cylinder each mode has a cutoff frequency and below that frequency there is no propagation. For tubes made of quartz and aluminum Lucite, we found that the existence of the cutoff frequencies depend on the degree of anisotropicattenuation, i.e., if the axial quality factor is greater than the transverse quality factor, the modes propagate at all frequencies. In contrast to the elastic case, the Poynting vector and the energy velocity have a component along the radial direction, whose values depend on the transverse attenuation. The presence of intrinsic attenuation confines the energy near the (elastic) cutoff frequencies while the radial distribution of the energy is governed by the geometrical features of the cylinder.
103(1998); http://dx.doi.org/10.1121/1.421240View Description Hide Description
The approximate theory of localized elastic waves in immersed solid wedges earlier developed for wedges with small values of the apex angle [V. V. Krylov, Proc. IEEE Ultrason. Symp., Cat. #94, CHO 793–796 (1994)] has predicted that the effect of water loading results in velocity decrease for wedge modes travelling in the subsonic regime of wave propagation. The results of this theory, in particular the absolute values of wedge wave velocity calculated for slender Plexiglas wedges, agree well with the corresponding experiments. The present study demonstrates that for relative values of wedge wave velocity, as compared with those for wedges in vacuum, this theory provides good quantitative agreement with the experiments on Plexiglas samples also for large values of the apex angle. In addition to this, a generalization of the theory is undertaken to describe the effect of heavier wedge material and a supersonic regime of wave propagation. The corresponding results show good agreement with the existing velocity measurements in immersed brass wedges.
Temporal deconvolution of laser-generated longitudinal acoustic waves for optical characterization and precise longitudinal acoustic velocity evaluation103(1998); http://dx.doi.org/10.1121/1.421241View Description Hide Description
The laser thermoelastic generation of ultrasound is a promising technique with many potential applications, but it is also a complicated process with many physical phenomena involved. Contrary to a conventional piezoelectric transducer generation, which is a surface phenomenon, a laser generation can activate acoustic sources within the material by optical penetration of the excitation wavelength, resulting in asynchronous wave arrivals at a given point. More generally, in the ideal case of a nondispersive isotropic material, the laser-ultrasonics displacement signals result from temporal convolutions between optical penetration, laser pulse duration, and laser spot extension effects. In this paper, a deconvolution technique is presented that extracts the laser pulse duration contribution from the experimental displacement signals. This deconvolution scheme applied to one-dimensional experiments, in which the laser excitation is spread over a sufficiently large area on the front side of the sample, allows the measurement of the optical absorption coefficient of the material at the excitation wavelength and also a precise evaluation of its longitudinal acoustic velocity.
- UNDERWATER SOUND 
High-frequency backscattering enhancements by thick finite cylindrical shells in water at oblique incidence: Experiments, interpretation, and calculations103(1998); http://dx.doi.org/10.1121/1.421200View Description Hide Description
Impulse response backscatteringmeasurements are presented and interpreted for the scattering of obliquely incident plane waves by air-filled finite cylindrical shells immersed in water. The measurements were carried out to determine the conditions for significant enhancements of the backscattering by thick shells at large tilt angles. The shells investigated are made of stainless steel and are slender and have thickness to radius ratios of 7.6% and 16.3%. A broadband PVDF (polyvinylidene fluoride) sheet source is used to obtain the backscattering spectral magnitude as a function of the tilt angle (measured from broadside incidence) of the cylinder. Results are plotted as a function of frequency and angle. These plots reveal large backscattering enhancements associated with elastic excitations at high tilt angles, which extend to end-on incidence in the coincidence frequency region. Similar features are present in approximate calculations for finite cylindrical shells based on full elasticity theory and the Kirchhoff diffraction integral. One feature is identified as resulting from the axial (meridional ray) propagation of the supersonic leaky Lamb wave. A simple approximation is used to describe circumferential coupling loci in frequency-angle space for several surface waves. The resulting loci are used to identify enhancements due to the helical propagation of the subsonic Lamb wave.
Double wave of Stoneley type on the interface of a stratified fluid layer and an elastic solid half-space103(1998); http://dx.doi.org/10.1121/1.421242View Description Hide Description
Sound propagation from a point time-harmonic source in a stratified water layer lying over an elastic solid half-space is investigated. It is assumed that the sound speed in the layer is less than the shear speed in the solid bottom, and that it increases with the depth. Numerical examples are given which show that the dependence of the wave field on the range between the source and the receiver can sharply change the character under rather small variations of the frequency. Namely, for some particular frequencies, the sound amplitude shows a periodical dependence on the range, while for other frequencies there is no periodicity. A theoretical explanation of this phenomenon is given in a mathematical development using the normal modes theory and high-frequency asymptotic approximations. The dispersion phase curves are found to have “quasi-intersections,” i.e., small domains where two adjacent curves almost intersect. The corresponding frequencies are called the “specific” frequencies. For any nonspecific frequency, there is one interface Stoneley mode, whilst for each specific frequency there are two modes of the Stoneley type with close phase velocities. The periodicity of the field is a result of interference in the two Stoneley modes.