Volume 107, Issue 2, February 2000
- acoustics research letters online
- acoustical news—usa
- acoustical news—international
- general linear acoustics 
- nonlinear acoustics 
- underwater sound 
- ultrasonics, quantum acoustics, and physical effects of sound 
- transduction 
- noise: its effects and control 
- architectural acoustics 
- acoustic signal processing 
- physiological acoustics 
- psychological acoustics 
- speech production 
- speech perception 
- speech processing and communication systems 
- bioacoustics 
- letters to the editor
Index of content:
- ACOUSTICS RESEARCH LETTERS ONLINE
107(2000); http://dx.doi.org/10.1121/1.428602View Description Hide Description
Acoustical imaging is based on the ability to focus an acoustic beam inside the zone of interest. This remains an issue through a high-order multiple scattering medium because the electronic delay lines that enable one to focus through a multiple scattering medium are a priori unknown. Using time-reversal principles, we show that images can be obtained through a very disordered medium. Surprisingly, the images are better than those obtained in a homogeneous medium with a classical imagingdevice.
- GENERAL LINEAR ACOUSTICS 
107(2000); http://dx.doi.org/10.1121/1.428250View Description Hide Description
Wave propagation of acoustic waves in porous media is considered. The medium is assumed to have a rigid frame, so that the propagation takes place in the air which fills the material. The Euler equation and the constitutive relation are generalized to take into account the dispersive nature of these media. It is shown that the connection between the fractional calculus and the behavior of materials with memory allows time-domain wave equations, the coefficients of which are no longer frequency dependent, to be worked out. These equations are suited for direct and inverse scattering problems, and lead to the complete determination of the porous medium parameters.
Backscattering enhancements for tilted solid plastic cylinders in water due to the caustic merging transition: Observations and theory107(2000); http://dx.doi.org/10.1121/1.428251View Description Hide Description
Bulk shear and longitudinal waves give rise to important contributions to the scattering of ultrasound by tilted finite plastic and rubber cylinders in water. This occurs in situations where either the shear or longitudinal speed is less than the speed of sound in the surrounding water. At a certain critical tilt angle, large backscattering enhancements are observed for finite cylinders, where the wave vector can reverse direction upon reflection from the cylinder truncation. The scattering process is analogous to the enhancement produced by the merging of rainbow caustics of primary rainbow rays in the scattering of light by long dielectric cylinders, also known as the caustic merging transition [C. M. Mount, D. B. Thiessen, and P. L. Marston, Appl. Opt. 37, 1534–1539 (1998)]. A ray theory was developed to model the backscattering mechanism at the critical tilt angle. It employs the idea of the Bravais effective refractive index, convenient for constructing ray diagrams for the projections of rays in the base plane of the cylinder. There is general agreement between the theory and the experiment down to relatively low ultrasonic frequencies (ka as small as 10). The enhancement is the most significant backscattering contribution for a wide range of tilt angles.
107(2000); http://dx.doi.org/10.1121/1.428252View Description Hide Description
A modified integral Werner method is used to calculate pressurescattered by an axisymmetric body immersed in a perfect and compressible fluid subject to a harmonic acoustic field. This integral representation is built as the sum of a potential of a simple layer and a potential of volume. It is equivalent to the exterior Helmholtz problem with Neumann boundary condition for all real wave numbers of the incident acoustic field. For elasticstructurescattering problems, the modified Werner method is coupled with an elastodynamic integral formulation in order to account for the elastic contribution of the displacement field at the fluid/structure interface. The resulting system of integral equations is solved by the collocation method with a quadratic interpolation. The introduction of a weighting factor in the modified Werner method decreases the number of volume elements necessary for a good convergence of results. This approach becomes very competitive when it is compared with other integral methods that are valid for all wave numbers. A numerical comparison with an experiment on a tungsten carbide end-capped cylinder allows a glimpse of the interesting possibilities for using the coupling of the modified Werner method and the integral elastodynamic equation used in this research.
107(2000); http://dx.doi.org/10.1121/1.428290View Description Hide Description
A new approach to the acoustics of closed spaces is developed that involves solutions for polygonal shapes in explicit form. It is shown that exact solutions can be constructed for polygonal geometries where all the interior angles are equal to (n is an integer). It is stated that the set of such polygons consists of the rectangle (known result) and three types of triangles. Some new explicit formulas are obtained for the eigenfrequencies of the triangles. It is demonstrated that the proposed technique also permits an exact representation of the impulse response function for the geometries described.
107(2000); http://dx.doi.org/10.1121/1.428254View Description Hide Description
The problem of acoustic radiation from a cylindrical pipe with an infinite flange has been discussed in a number of papers. The most common approach is to decompose the field inside the pipe over a basis of Bessel functions. A very large number of basis functions is usually required, with a large degree of ripple appearing as an artifact in the solution. In this paper it is shown that a close analysis of the velocity field near the corner yields a new family of functions, which are called “edge functions.” Using this set of functions as test functions and applying the moment method on the boundary between the waveguide and free space, a solution is obtained with greatly improved convergence properties and no ripple.
107(2000); http://dx.doi.org/10.1121/1.428255View Description Hide Description
The properties of intensity streamlines and vorticity streamlines are discussed in this paper. It is found that the properties in three-dimensional sound fields are different from the properties in two-dimensional sound fields. The integral behavior of intensity streamlines is that the beginning and the end are attached to a sound source surface or that the beginning is on the sound source surface and the end extends into the infinite. For the vorticity streamlines, the integral behavior is that it is a closed curve or that the beginning and the end are attached to the sound source surface. Three examples are given for intensity and vorticity streamlines.
- NONLINEAR ACOUSTICS 
Modified impulse method for the measurement of the frequency response of acoustic filters to weakly nonlinear transient excitations107(2000); http://dx.doi.org/10.1121/1.428256View Description Hide Description
In this paper, a modified impulse method is proposed which allows the determination of the influence of the excitation characteristics on acoustic filter performance. Issues related to nonlinear propagation, namely wave steepening and wave interactions, have been addressed in an approximate way, validated against one-dimensional unsteady nonlinear flow calculations. The results obtained for expansion chambers and extended duct resonators indicate that the amplitude threshold for the onset of nonlinear phenomena is related to the geometry considered.
- UNDERWATER SOUND 
107(2000); http://dx.doi.org/10.1121/1.428257View Description Hide Description
An approach for avoiding the problem of environmental uncertainty is tested using data from the TESPEX experiments. Acoustic data basing is an alternative to the difficult task of characterizing the environment by performing direct measurements and solving inverse problems. A source is towed throughout the region of interest to obtain a database of the acoustic field on an array of receivers. With this approach, there is no need to determine environmental parameters or solve the wave equation. Replica fields from an acoustic database are used to perform environmental source tracking [J. Acoust. Soc. Am. 94, 3335–3341 (1993)], which exploits environmental complexity and source motion.
107(2000); http://dx.doi.org/10.1121/1.428258View Description Hide Description
Internal waves of a given strength will produce acoustic effects that vary from water mass to water mass. Presented here is a means of predicting the strength of acoustic fluctuations due to internal waves, given the basic climatology, that is, measurements of depth, temperature, and salinity of an oceanic region. An acoustic fluctuation strength parameter F is defined as the ratio of the fractional potential sound-speed change to the fractional potential-density change. Here F is calculated at three depth levels (275, 550, and 850 m), on a one-degree grid of latitude and longitude, using NODC/OCL’s World Ocean Atlas 1994. Representative values of F are presented for 15 upper water masses that range from in the North Pacific to in the North Atlantic, with a typical value for most of the upper waters being Results for two depth levels within 12 intermediate water masses range from in the North Pacific to in the North Atlantic, with a typical value of although there is considerable variation. In general, F exhibits higher values in the Atlantic Basin than in the Indian or Pacific, and has a maximum at 550 m. The main use of F will be the prediction of travel-time fluctuations in acoustic propagation experiments, which will be proportional to the value of F, given a universal strength of internal waves.
107(2000); http://dx.doi.org/10.1121/1.428259View Description Hide Description
A year of surf noise observations in the very near shore region of La Jolla Shores beach are presented. Ambient sound levels and surface wave height were recorded for 9 min every hour from July 1997 through June 1998 at a monitoring station located 360 m seaward of the beach in 8-m deep water. Sound segments that were dominated by the noise from breaking surf formed the basis of a correlation analysis between surf noise level and wave height, wave period, wind speed, and mean water depth. The analysis shows that surf noise is primarily determined by wave height, and scales approximately with the wave height squared. The surface wave energy flux onto the beach also scales with wave height squared, leading to the conclusion that the conversion of the mechanical energy of the surface wave field into noiseenergy is approximately constant. In fact, the ratio of noiseenergy to surface wave energy flux varies by up to a factor of 3 over the range of energy fluxes considered (100–3000 W per m).
107(2000); http://dx.doi.org/10.1121/1.428253View Description Hide Description
Bubble plumes of various void fractions and sizes were produced by varying the flow velocity of a water jet impinging normally on a water surface. The bubbles entrained at the surface were carried downwards by the fluid flow to depths ranging from 33 to 65 cm, and formed roughly cylindrical plumes with diameters ranging from 12 to 27 cm. The acoustic emissions from the plumes were recorded onto digital audio tape using a hydrophone placed outside the cloud at distances ranging from 50 cm to 16.0 m. Closeup video images of the individual bubbles within the plume were also taken in order to gain knowledge of the bubble size distributions. The experiments were performed in both fresh-water and salt-water environments. The fresh-water clouds emitted sounds with a modal structure that was significantly different from that produced by the salt-water clouds. Furthermore, the smaller bubbles present in the salt-water clouds have a fundamental effect on the amplification of turbulencenoise, generating sound at significant levels for frequencies up to several hundred Hertz.
- ULTRASONICS, QUANTUM ACOUSTICS, AND PHYSICAL EFFECTS OF SOUND 
Ultrasonic absorption in critical binary mixture of perfluoromethylcyclohexane and carbon tetrachloride107(2000); http://dx.doi.org/10.1121/1.428260View Description Hide Description
The results of ultrasonic absorption and velocity measurements for the system perfluoromethylcyclohexane-carbon tetrachloride are presented. In addition, viscosity measurements were made. Ultrasonic absorption at 5, 7, 10, 15, 21, and 25 MHz, above critical temperature is analyzed using the dynamic scaling theory of Ferrell and Bhattacharjee. The values of vs show a good agreement with the theory. The experimental values of for the binary mixture are compared to the scaling function
Comparison between the dispersion curves calculated in complex frequency and the minima of the reflection coefficients for an embedded layer107(2000); http://dx.doi.org/10.1121/1.428262View Description Hide Description
Analytical solutions of Lamb functions for symmetric and antisymmetric elastodynamic modes propagating within a solid layer embedded in an infinite medium are presented. Alternative theoretical analyses of such modes are performed, first in terms of the usual approach of harmonic heterogeneous plane waves (real frequency and complex slowness) and then in terms of transient homogeneous plane waves (complex frequency and real slowness). An example structure of a 0.1-mm-thick “alpha case” (an oxygen-rich phase of titanium that is relatively stiff) plate embedded in titanium is used for the study. A large difference between the usual dispersion curves calculated in real frequency and complex slowness and those calculated in complex frequency and real slowness is shown. Thus the choice between a spatial and a temporal parameter to describe the imaginary part of the guided waves is shown to be significant. The minima and the zeros of the longitudinal and shear plane-wave reflection coefficients are calculated and are compared with the dispersion curves. It is found that they do not match with the dispersion curves for complex slowness, but they do agree quite well with the dispersion curves for complex frequency. This implies that the complex frequency approach is better suited for the comparison of the modal properties with near-field reflection measurements.
107(2000); http://dx.doi.org/10.1121/1.428263View Description Hide Description
Traditional broadband transmission method for measuring acoustic dispersion requires the measurements of the sound speed in water, the thickness of the specimen, and the phase spectra of two transmitted ultrasound pulses. When the sound speed in the specimen is significantly different from that in water, the overall uncertainty of the dispersion measurement is generally dominated by the uncertainty of the thickness measurement. In this paper, a new water immersion method for measuring dispersion is proposed which eliminates the need for thickness measurement and the associated uncertainty. In addition to recording the two transmitted pulses, the new method requires recording two reflected pulses, one from the front surface and one from the back surface of the specimen. The phase velocity as well as the thickness of the specimen can be determined from the phase spectra of the four pulses. Theoretical analysis and experimental results from three specimens demonstrate the advantages of this new method.
107(2000); http://dx.doi.org/10.1121/1.428264View Description Hide Description
ResonantUltrasound Spectroscopy (RUS) of a spherical sample in a pressurizing gas atmosphere was investigated experimentally and theoretically. Measurements were made on a fused silica sphere in He, Ar, and gases up to pressures of 120 bar. The pressure-dependent shift in the resonant frequency, and the Q-factor were measured for the S00, S11, and T02 modes. A theoretical model based on acoustic radiation impedance was used to calculate and the radiation-resistance component, of the Q-factor. Agreement between theory and experiment was good for but there were discrepancies for It was found that the theoretical due to gas-loading effects associated with acoustic radiation was very small and consistent with the observed dependence on pressure and gas species for the T02 mode but not for the S00 and S11 modes. We conclude that the T02 mode is the most reliable of these modes to use in measuring third-order elastic constants by RUS.
107(2000); http://dx.doi.org/10.1121/1.428261View Description Hide Description
The recent experimental results of J. Holzfuss, M. Rüggeberg, and R. Mettin [Phys. Rev. Lett. 81, 1961 (1998)] in which a second harmonic drive system was used to generatesonoluminescence (SL) have been analyzed in the context of the dissociation hypothesis (DH) of D. Lohse and S. Hilgenfeldt [J. Chem. Phys. 107, 6986 (1997)]. The second harmonic introduces two more variables that are under experimental control: a phase and an additional pressure term to the acoustic drive pressure. Diffusive equilibrium curves for a fixed gas concentration were calculated as was the Mach criterion. A phase space diagram was constructed to permit the prediction of regions of stable SL, unstable SL, stable non-SL, and unstable non-SL. These were compared to Holzfuss' experimental observations, and excellent quantitative agreement was seen. The results provide further evidence that the underlying assumptions of DH are sound. They also indicate the utility of DH for determining appropriate experimental conditions to achieve SL and for optimizing an experimental system.