Volume 104, Issue 3, September 1998
- acoustical news—usa
- book reviews
- reviews of acoustical patents
- selected research articles 
- general linear acoustics 
- nonlinear acoustics, macrosonics 
- aeroacoustics, atmospheric sound 
- underwater sound 
- ultrasonics, quantum acoustics, and physical effects of sound 
- transduction 
- structural acoustics and vibration 
- noise: its effects and control 
- architectural acoustics 
- acoustical measurements and instrumentation 
- physiological acoustics 
- psychological acoustics 
- speech perception 
- speech processing and communication systems 
- music and musical instruments 
- bioacoustics 
- letters to the editor
- program abstracts of the 136th meeting of the acoustical society of america
Index of content:
- REVIEWS OF ACOUSTICAL PATENTS
104(1998); http://dx.doi.org/10.1121/1.424267View 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 
104(1998); http://dx.doi.org/10.1121/1.424323View Description Hide Description
An analytical investigation is made of the compression wave generated when a high-speed train enters a long tunnel with distributed venting. The compression wave amplitude is determined by train speed and the area ratio of the train and tunnel, but its rise time depends principally on the geometry of the tunnel entrance. Vented tunnel entrance “hoods” are frequently used to increase the rise time, in order to reduce the impact of the micro-pressure pulse radiated from the tunnel exit when the compression wave arrives at the far end of the tunnel. Approximate calculations are performed to determine the initial rise time for a tunnel of rectangular cross section with a continuously variable vented roof near the entrance, for train Mach numbers less than about 0.2 (∼150 mph). The distribution of venting apertures can be optimized to maximize rise time, and a sixfold increase is shown to be possible when the aperture distribution decreases exponentially with distance into the tunnel. The method of this paper is applicable also to more general tunnel entrance geometries, and for higher train Mach numbers.
104(1998); http://dx.doi.org/10.1121/1.424324View Description Hide Description
In behavioral experiments where real targets are used to investigate dolphin echolocation, it is often very difficult to extract the relevant echo parameters that the animals use to discriminate or classify. The complex relationship between the physical dimensions and the reflection characteristic of real targets prevents separate control of various echo parameters of the stimuli presented in an echolocation experiment. A new echo simulation method presented in this paper avoids this problem. Dolphin echolocation sounds are transformed with the target impulse response into artificial echoes, which are played back to the animal. The phantom echo system is implemented on a digital signal processing board and gives an experimenter fully programmable control over the echo generating process and the echo structure itself. Echoes of several underwater targets were simulated to evaluate the quality of the method. A comparison of simulated echoes with the original echoes demonstrated very good agreement independent of the incident signal (cross-correlation coefficient ). The method has tremendous potential for investigating animal echolocation and understanding biosonarsignal processing.
- GENERAL LINEAR ACOUSTICS 
104(1998); http://dx.doi.org/10.1121/1.424325View Description Hide Description
Accurate simulation of wave propagation around subwavelength geometries using standard finite-difference time-domain(FDTD) techniques require a fine spatial and temporal sampling resulting in high computational costs. In this paper an extension to this standard FDTD technique is proposed by means of quasi-stationary solutions on a subwavelength scale. The FDTDequations in the region near the subwavelength geometry are extended with some correction terms of which the magnitude is extracted from the quasi-stationary pressure distribution around these geometries. These pressure distributions can be calculated from the Laplace equation. Using this new technique, FDTD simulations can be based on a more coarse grid, thus reducing computational cost considerably. The accuracy of this technique is mainly determined by the accuracy of the Laplace solutions. This technique was tested with success on the simulation of resonators. It was also shown that the new FDTDequations can be extended to include viscosityeffects.
The radiating near-field asymptotics of a normal time-harmonic circular ultrasonic transducer in an elastic half-space104(1998); http://dx.doi.org/10.1121/1.424326View Description Hide Description
The modern diffraction theory is applied to analyze the radiating near zone of a normal time-harmonic circular transducer directly coupled to a homogeneous and isotropic solid. The two-tier asymptotic approach is used first to find the far-field asymptotics of a point source and then the radiating near-field asymptotics of the circular transducer. All the known ray-theoretical solutions for body waves, such as the plane P wave and the toroidal edge waves, both P and S, are obtained. The non-ray-theoretical solutions, such as the edge waves present in the axial boundary layer and the total field inside the penumbral boundary layer, are also described. The asymptotic formulas produced all have immediate physical interpretation, give explicit dependence on model parameters and involve in geometrical region elementary functions and inside boundary layers, well-known special functions. It is argued that asymptotic results may be used to write computer codes which simulate the radiating near field of the circular transducer orders of magnitude faster than the exact numerical schemes, but more accurately than other known approximations.
High-frequency asymptotic description of head waves and boundary layers surrounding the critical rays in an elastic half-space104(1998); http://dx.doi.org/10.1121/1.424327View Description Hide Description
The high-frequency asymptotic description of head waves as well as the field inside boundary layers surrounding the critical rays are obtained for two cases: (a) a point source, and (b) a circular transducer, both acting normally on an isotropic and homogeneous elastic half-space. The edge head waves underneath a circular transducer are described by the asymptotics of a higher order compared to those of direct compressional, edge compressional, and shear waves, but are still discernible in the radiating near zone and thus might be useful in nondestructive evaluation of industrial materials. The asymptotic formulas produced involve in geometrical zones elementary functions and inside boundary layers well-known special functions. Therefore, they allow us to elucidate the physics of the problem and can be used in writing computer codes which simulate the radiating near field of a circular transducer orders of magnitude faster than full numerical schemes. The formulas have been tested against exact integral solutions evaluated numerically.
Padé approximants for the acoustical properties of rigid frame porous media with pore size distributions104(1998); http://dx.doi.org/10.1121/1.424328View Description Hide Description
Expressions for the viscosity correction function, and hence bulk complex impedance, density, compressibility, and propagation constant, are obtained for a rigid frame porous medium whose pores are prismatic with fixed cross-sectional shape, but of variable pore size distribution. The low- and high-frequency behavior of the viscosity correction function is derived for the particular case of a log-normal pore size distribution, in terms of coefficients which can, in general, be computed numerically, and are given here explicitly for the particular cases of pores of equilateral triangular, circular, and slitlike cross-section. Simple approximate formulae, based on two-point Padé approximants for the viscosity correction function are obtained, which avoid a requirement for numerical integration or evaluation of special functions, and their accuracy is illustrated and investigated for the three pore shapes already mentioned.
Transient wave propagation in a circular annulus subjected to transient excitation on its outer surface104(1998); http://dx.doi.org/10.1121/1.424329View Description Hide Description
The objective of this work is to investigate the propagation of guided transient waves in the circumferential direction of annular structural components. For this purpose, a two-dimensional circular annulus is considered. It is assumed that the inner surface of the annulus is traction free and the outer surface of the annulus is subjected to a time-dependent transient excitation. The guided circumferential waves induced by this transient excitation are studied in detail to understand the propagation characteristics of various wave modes. The method of eigenfunction expansion is used to solve the transient wave propagation problem. To this end, the problem of time harmonic, steady-state circumferential waves is solved first as the eigenfunctions. The time-dependent response of the annulus is then obtained by superimposing all eigenfunctions over all possible frequencies. Several numerical examples are given to illustrate the method of solution and to provide some guidelines on using guided waves to detect radial cracks in annular structural components.
An equivalent source technique for calculating the sound field inside an enclosure containing scattering objects104(1998); http://dx.doi.org/10.1121/1.424330View Description Hide Description
The equivalent source method has previously been used to calculate the exterior sound field radiated or scattered from bodies in the free-field. In this paper the method is used to calculate the internal pressure field for an enclosure which can have arbitrary boundary conditions and may include internal objects which scatter the sound. Some of the equivalent source positions are chosen to be the same as the first order images of the source inside the enclosure, some are positioned within the scattering objects, and the remainder are positioned on a spherical surface some distance outside the enclosure. The normal velocity on the surfaces of the scattering objects and the enclosure walls is evaluated at a larger number of positions than there are equivalent sources. The sum of the squared difference between this velocity and that expected because of the admittance of the boundary, is minimized by adjusting the strengths of the equivalent sources. The convergence of the method is checked by evaluating the velocity at a larger number of monitoring positions. Example results are presented for the sound field and frequency response inside a damped rectangular enclosure, which compare very well with the conventional modal model. The effect of having rigid spheres inside the enclosure are then investigated, and it is found that the effect is significant even some distance from the spheres and at frequencies for which the size of the sphere is small compared to a wavelength. Finally the effect of a nonlocally reacting boundary condition is illustrated by assuming that one of the walls of the enclosure is an elastic plate.
104(1998); http://dx.doi.org/10.1121/1.424331View Description Hide Description
Reflection and transmission of an ultrasonic beam by a homogeneous polymer plate (PMMA) immersed in water are studied experimentally and theoretically by the interference method. The elementary waves which emerge from the plate after 0, 1, or 2 internal reflections on the lower interface are considered individually, and their amplitude and phase shift are calculated. The interferences between these elementary waves provide the resulting waves reflected and transmitted by the plate. This method is valid because only a small number of these elementary waves have a significant amplitude when they emerge, due to the relatively high wave attenuation of polymer materials. For a 2-mm-thick PMMA plate, for example, only two internal reflections on the lower face must be taken into account for the reflection by the plate, and one for transmission. Perfect agreement with results from the classical global method confirms the validity of the interference method. This treatment enables us to better understand the physical significance of the reflection and transmission curves by the plates. Moreover, this method facilitates the calculation of accurate ultrasonic parameter values of the plate (velocities and attenuation coefficients of the longitudinal and transverse waves), by adjustment of the theoretical to the experimental reflection and transmission curves.
Near-field ultrasonic scattering from a cavity in steel considering the velocity amplitude on the transducer face using an error function model104(1998); http://dx.doi.org/10.1121/1.424332View Description Hide Description
The influence of nonuniform transducervelocity distribution in the near-field echo formation scattered from a cavity in steel is analyzed. In the present study, the velocity amplitude on the transducer face was modeled using an offset error function. Using this distribution, the echo waveforms scattered from a cylinder cavity in steel were estimated and compared with the echo estimated using uniform distribution and echo observed experimentally. The estimation accuracy of the near-field echo waveforms were improved quantitatively.
104(1998); http://dx.doi.org/10.1121/1.424333View Description Hide Description
It is shown that the dispersive Rayleigh wave propagating around a concave cylindrical surface is substantially less attenuated by fluid loading than the corresponding wave on a flat surface. First, the analytical solution for vertically polarized shear wavescattering from a fluid-filled cylindrical cavity is formulated in the time domain, then the signal of interest is gated out and spectrum analyzed in order to numerically predict the attenuation caused by leakage into the fluid. On a concave surface the ratio of the normal and transverse displacement components produced by the circumferential creeping wave is lower than that of the ordinary Rayleigh wave propagating on a flat surface, which explains the reduced leaky attenuation caused by fluid loading. Experiments were carried out to verify these analytical predictions. The fluid-loading induced semicircumferential loss of the circumferential creeping wave around a cylindrical cavity was found to be in excellent agreement with the experimental measurements over a wide frequency range.
104(1998); http://dx.doi.org/10.1121/1.424334View Description Hide Description
A new method, the edge element method, has been developed to numerically evaluate a variety of ultrasonic transducer beam models. The edge element technique divides the transducer surface into a web of sources consisting of radiating straight line elements whose individual contributions can be evaluated analytically. When all of these edge elements are summed, the wave field of the transducer can be obtained at any field point in the surrounding medium for a given ultrasonic frequency. To demonstrate the versatility of this approach, it is shown that edge elements can accurately model the wave fields radiated into a fluid by focused and unfocused transducers of circular and noncircular apertures.
104(1998); http://dx.doi.org/10.1121/1.424335View Description Hide Description
An analytical/experimental approach is presented to reconstruct the space–time pressure field in a plane and forward project the resultant space–time pressure field using tomographic and wave vector time-domain methods. Transient pressure signals from an underwater ultrasonic planar transducer are first measured using a line fiber-optic pressuresensor which is scanned across a plane at a fixed distance from the transducer. The resulting spatial line integrals in the plane are time-dependent signals which are first used to reconstruct the space–time pressure field in the plane via simply implemented tomographic methods. These signals are then used to forward project the space–time pressure field to arbitrary planes employing a wave vector time-domain method. Verification of the method is first presented using synthetic signals and the impulse response approach. An experimental verification of the approach is then presented using an ultrasonic planar transducer. The results of the projected and experimental fields are compared at various distances for synthetic signals and experimental data. Good correlation is found between the calculated, projected, and experimental data.
- NONLINEAR ACOUSTICS, MACROSONICS 
104(1998); http://dx.doi.org/10.1121/1.424336View Description Hide Description
In order to evaluate the possible side effects of diagnosticmedicalultrasound, and in particular the effects of nonlinear propagation of sound, it is necessary to characterize the scanners used. To this end, the acoustic field emitted by a phased-array Hitachi EUB-26 ultrasoundscanner operating in a strongly focused mode was measured a small distance from the scanner head, and the velocity field at the surface of the head deduced. A finite difference model was then used to propagate the pressure field beyond the focus, taking into account nonlinear effects, attenuation and diffraction, and the result compared with observations in water, giving reasonable agreement out to the scanplane focus. The extrapolated field was then examined in detail, revealing those regions in which most power is lost to the medium, some of which are off-axis, and so might not be detected by normal calibration procedures.
104(1998); http://dx.doi.org/10.1121/1.424337View Description Hide Description
A chamber cavity, which has a square cross section and pressure-release walls, is used to produce a well-defined, 160-kHz standing ultrasonic field. A suspension of latex microspheres in aqueous metrizamide fills the chamber. The chamber rotates about a horizontal axis producing the centripetal force necessary to contain the buoyant spheres in the axial region. At low particle concentrations, clusters of microspheres form at half-wavelength intervals near the axial positions of acoustic pressure amplitude minima, as expected because of rotational and acoustic radiation forces. At higher concentrations, additional particle distributions are often seen that suggest the presence of flow. When high concentrations of larger particles are used, small clusters also form at axial positions of maxima. Theory for acoustic streaming in a rotating fluid predicts flow speeds that are too small to account for the observed flow. Reasonable agreement with observations is obtained using a theory for flowgenerated by the buoyant gravitational force acting on the clusters.