• Volume/Page
  • Keyword
  • DOI
  • Citation
  • Advanced
   
 
 
 

Journal of the Acoustical Society of America

BROWSE VOLUMES

Year Range: 
Search Issue | RSS Feeds RSS
Previous Issue Next Issue

Nov 2004

Volume 116, Issue 5, pp. 2697-3225

Return to All Sections
back to top
RSS Feeds

Full wave modeling of therapeutic ultrasound: Efficient time-domain implementation of the frequency power-law attenuation

Marko Liebler, Siegfried Ginter, Thomas Dreyer, and Rainer E. Riedlinger

J. Acoust. Soc. Am. Volume 116, Issue 5, pp. 2742-2750 (2004); (9 pages) | Cited 11 times

Online Publication Date: 09 Nov 2004

Full Text: Read Online (HTML) | Download PDF

Show Abstract
For the simulation of therapeutic ultrasound applications, a method including frequency-dependent attenuation effects directly in the time domain is highly desirable. This paper describes an efficient numerical time-domain implementation of the power-law attenuation model presented by Szabo [Szabo, J. Acoust. Soc. Am. 96, 491–500 (1994)]. Simulations of therapeutic ultrasound applications are feasible in conjunction with a previously presented finite differences time-domain (FDTD) algorithm for nonlinear ultrasound propagation [Ginter et al., J. Acoust. Soc. Am. 111, 2049–2059 (2002)]. Szabo implemented the empirical frequency power-law attenuation using a causal convolutional operator directly in the time-domain equation. Though a variety of time-domain models has been published in recent years, no efficient numerical implementation has been presented so far for frequency power-law attenuation models. Solving a convolutional integral with standard time-domain techniques requires enormous computational effort and therefore often limits the application of such models to 1D problems. In contrast, the presented method is based on a recursive algorithm and requires only three time levels and a few auxiliary data to approximate the convolutional integral with high accuracy. The simulation results are validated by comparison with analytical solutions and measurements. © 2004 Acoustical Society of America.
Show PACS
43.20.Bi Mathematical theory of wave propagation
43.20.Hq Velocity and attenuation of acoustic waves
43.35.Bf Ultrasonic velocity, dispersion, scattering, diffraction, and attenuation in liquids, liquid crystals, suspensions, and emulsions

Singly focused backscattering from small targets in an Airy caustic formed by a curved reflecting surface

Benjamin R. Dzikowicz and Philip L. Marston

J. Acoust. Soc. Am. Volume 116, Issue 5, pp. 2751-2758 (2004); (8 pages) | Cited 1 time

Online Publication Date: 09 Nov 2004

Full Text: Read Online (HTML) | Download PDF

Show Abstract
When sound scatters off a curved-reflecting surface such as the ocean floor or surface, it can focus forming caustics in the water column. The simplest caustic is an Airy caustic formed by the merging of two rays. In a backscattering experiment with a target residing at or near an Airy caustic, a signal can be focused on the way to the target, upon return from the target, or in both directions. To investigate these processes, an experiment is conducted in which an Airy caustic is formed using a cylindrical half-pipe reflector. The backscattered echo focused only once, either to or from a spherical target, is examined here. These focused echoes can be significantly stronger than the simple direct echo. Approximations are examined where the echo amplitude changes with target position in proportion to an Airy function. The argument of the Airy function is calculated using the relative echo times of transient pulses. This result is extended by applying the uniform approximation method of Chester, Friedman, and Ursell.© 2004 Acoustical Society of America.
Show PACS
43.20.El Reflection, refraction, diffraction of acoustic waves
43.30.Gv Backscattering, echoes, and reverberation in water due to combinations of boundaries
43.20.Dk Ray acoustics

Propagation of sound in long enclosures

K. M. Li and K. K. Iu

J. Acoust. Soc. Am. Volume 116, Issue 5, pp. 2759-2770 (2004); (12 pages) | Cited 6 times

Online Publication Date: 09 Nov 2004

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The propagation of sound in long enclosures is addressed theoretically and experimentally. In many previous studies, the image source method is frequently used. However, these early theoretical models are somewhat inadequate because the effect of multiple reflections in long enclosures is often modeled by the incoherent summation of contributions from all image sources. Ignoring the phase effect, these numerical models are unlikely to be satisfactory for use in predicting intricate patterns of interference due to contributions from each image source. In the present paper, the effect of interference is incorporated by coherently summing the contributions from the image sources. To develop a simple numerical model, the walls of long rectangular enclosures are represented by either geometrically reflecting or impedance boundaries. Measurements in a one-tenth-scale model are conducted to validate the numerical model. In some of the scale-model experiments, the enclosure walls are lined with a carpet to simulate the impedance boundary condition. It has been shown that the proposed numerical model agrees reasonably well with experimental data. © 2004 Acoustical Society of America.
Show PACS
43.20.Fn Scattering of acoustic waves
43.20.Mv Waveguides, wave propagation in tubes and ducts
43.28.Js Numerical models for outdoor propagation
43.50.Ki Active noise control

On the interference between the two microphones in free-field reciprocity calibration

Salvador Barrera-Figueroa, Knud Rasmussen, Finn Jacobsen, and Lorenzo Muñíz

J. Acoust. Soc. Am. Volume 116, Issue 5, pp. 2771-2778 (2004); (8 pages) | Cited 1 time

Online Publication Date: 09 Nov 2004

Full Text: Read Online (HTML) | Download PDF

Show Abstract
One of the fundamental assumptions in free-field reciprocity calibration of microphones is that the microphones can be substituted by point sources at the positions where the acoustic centers are located. However, in practice the microphones have finite dimensions and, at the distance and in the frequency range where the measurements are made, the direct wave and the subsequent reflections from the microphones interfere with each other, creating a “standing wave.” This interference effect gives rise to deviations from the inverse distance law, indicating that the free-field assumption is not strictly valid. The interference has been thought to be caused by specular reflection between the parallel diaphragms of the microphones, and a solution based on tilting the axis of one of the microphones a few degrees has been proposed, but never examined in practice. In this paper a time-selective technique is applied for analyzing the interference and for removing it in the time domain. It is shown that the phenomenon is due to multiple backscattering rather than specular reflection. Thus tilting one of the microphones does not alleviate the problem, as also demonstrated experimentally. However, the time-selective technique is quite effective in removing the interference effect and other disturbances from the direct wave between the microphones. © 2004 Acoustical Society of America.
Show PACS
43.20.Fn Scattering of acoustic waves
43.20.Ye Measurement methods and instrumentation
43.38.Kb Microphones and their calibration
43.58.Vb Calibration of acoustical devices and systems

Single-channel time reversal in elastic solids

Alexander M. Sutin, James A. TenCate, and Paul A. Johnson

J. Acoust. Soc. Am. Volume 116, Issue 5, pp. 2779-2784 (2004); (6 pages) | Cited 9 times

Online Publication Date: 09 Nov 2004

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Reverberant volume time reversal in 3D elastic solids (doped glass and Berea sandstone) using a single channel are presented. In spite of large numbers of mode conversions (compressional to shear wave conversions at the walls), time reversal works extremely well, providing very good spatial and time focusing of elastic waves. Ceramics were bonded to the surface as sources (100–700 kHz); a broadband laser vibrometer (dc—1.5 MHz) was used as detector. Temporal and spatial time-reversal focusing are frequency dependent and depend on the dissipation characteristics of the medium. Doped glass (inverse dissipation Q between 2000 to 3000) shows time-reversed spatial focal resolution at about half of the shear wavelength. The Berea sandstone (Q = 50) yields a wider focusing width (a bit more than the shear wavelength) due to its lower Q. Focusing in the doped glass is better because the time-reversal (virtual) array created by wave reflections is larger than in the highly attenuating sandstone. These are the first results reported in granular media, and are a first step toward geophysical and field applications. © 2004 Acoustical Society of America.
Show PACS
43.20.Gp Reflection, refraction, diffraction, interference, and scattering of elastic and poroelastic waves
43.20.Jr Velocity and attenuation of elastic and poroelastic waves
43.20.Ye Measurement methods and instrumentation
43.35.Cg Ultrasonic velocity, dispersion, scattering, diffraction, and attenuation in solids; elastic constants

On the design of long T-shaped acoustic resonators

Deyu Li and Jeffrey S. Vipperman

J. Acoust. Soc. Am. Volume 116, Issue 5, pp. 2785-2792 (2004); (8 pages) | Cited 3 times

Online Publication Date: 09 Nov 2004

Full Text: Read Online (HTML) | Download PDF

Show Abstract
In this work we present a more general mathematical model for the calculation of resonance frequencies for long, T-shaped acoustic resonators. The method is based upon wave propagation and, unlike previous theories, no constraints on the geometry of the resonator are imposed. In addition, a new end-correction model based upon Rayleigh’s end corrections is proposed and evaluated. The theory is used to develop a plane-wave multimodal-based design theory, which permits higher-order 1-dimensional modes of the T-shaped acoustic absorber to be used for absorbing high-frequency noise within enclosures. A series of experiments are conducted on round and square cross section resonators to validate the theory, evaluate the end correction models, and demonstrate design examples. © 2004 Acoustical Society of America.
Show PACS
43.20.Ks Standing waves, resonance, normal modes
43.20.Mv Waveguides, wave propagation in tubes and ducts
43.50.Gf Noise control at source: redesign, application of absorptive materials and reactive elements, mufflers, noise silencers, noise barriers, and attenuators, etc.

A model for the radiated field of a plane piston after reflection from a curved surface

Adrian Neild, David A. Hutchins, Toby J. Robertson, and David W. Schindel

J. Acoust. Soc. Am. Volume 116, Issue 5, pp. 2793-2801 (2004); (9 pages) | Cited 2 times

Online Publication Date: 09 Nov 2004

Full Text: Read Online (HTML) | Download PDF

Show Abstract
A theoretical model is described for the field resulting from reflection of a plane piston source from a curved surface. The approach is based on an impulse response model, which treats the surface of the mirror as a grid of point reflectors to give an overall reflective response. The model was verified by comparison to experimental measurements in air, using a polymer-filmed capacitive transducer source fitted with an optical-grade mirror, at frequencies up to 1 MHz. The design parameters of such a device were investigated in order to determine the effect on the focal area, and to indicate how this model could be used to optimize the focusing effect of such a system. © 2004 Acoustical Society of America.
Show PACS
43.20.Rz Steady-state radiation from sources, impedance, radiation patterns, boundary element methods

The comb waveform as an efficient method for wideband transducer measurements

Walter H. Boober, Gorham G. Lau, Kim C. Benjamin, and Kenneth M. Walsh

J. Acoust. Soc. Am. Volume 116, Issue 5, pp. 2802-2806 (2004); (5 pages)

Online Publication Date: 09 Nov 2004

Full Text: Read Online (HTML) | Download PDF

Show Abstract
An efficient acoustic calibration technique based on a uniformly weighted comb waveform is presented. The method takes advantage of the linear, time invariant nature of the measurement configuration and the comb’s wide bandwidth to capture all spectral components of interest for a device under test in a single ping. Measured results comparing single ping comb measurements with conventionally obtained tonal measurements are presented. The examples given illustrate the accuracy and utility of this technique for the calibration of broadband systems. © 2004 Acoustical Society of America.
Show PACS
43.20.Ye Measurement methods and instrumentation
43.30.Xm Underwater measurement and calibration instrumentation and procedures
43.58.Vb Calibration of acoustical devices and systems
Return to All Sections
Close

Home Publications Meetings Contact ASA Site Map Back to Top

Copyright © Acoustical Society of America

close