摘要:

Abstract not available.

ISSN:0001-4966    

DOI:10.1121/1.421028

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

Abstract not available.

ISSN:0001-4966    

DOI:10.1121/1.419871

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

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 athttp://www.uspto.gov.

ISSN:0001-4966    

DOI:10.1121/1.419874

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

An active sonar using Polaroid electrostatic transducers positioned at the end of a robot arm is described that adaptively changes its location and configuration in response to the echoes it observes in order to recognize an object. The sonar mimics biological echo-location systems, such as those employed by bats and dolphins, in that there is a center transmitter flanked by two adjustable receivers, the sonar has rotational and translational mobility, and the echo processing contains elements that have been observed in the mammalian auditory system. Using information in the echoes, the sonar translates in a horizontal plane and rotates in pitch and yaw to position an object at a standard location within the beam patterns. The transmitter points at the object to maximize the incident acoustic intensity and the receivers rotate to maximize the echo amplitude and the bandwidth, and to minimize the echo-producing region. This procedure results in a unique echo vector associated with each object at a given object pose. Recognition is accomplished by extracting 32 values from the binaural echo patterns and searching a data base that is constructed during a learning phase. The system operation is illustrated by having it recognize rubber O-rings of different sizes and by differentiating the head and tail sides of a coin.

ISSN:0001-4966    

DOI:10.1121/1.419658

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

Many ultrasonic nondestructive testing applications have cylindrical geometries. Examples involve the excitation of ultrasound by cylindrical piezoelectic probes or by laser, x rays, electron beams [A. C. Tam, Rev. Mod. Phys.58, 381–431 (1986)], or ion beams [L. Sulak et al., Nucl. Instrum. Methods161, 203–217 (1979)]. Thus, calculations of cylindrical wave propagation are important for a better understanding and interpretation of many testing situations. This paper deals with the AFIT Code or finite volume method for numerical simulation of sound propagation in fluids adapted to cylindrical geometries (CAFIT). A comparison is made with standard difference-equations techniques also utilized for cylindrical geometries. Two examples are dealt with: (1) The sound generation by a high energy beam of heavy ions stopping in water; (2) the multimode sound propagation in a medical doppler injection device excited by a disk probe.

ISSN:0001-4966    

DOI:10.1121/1.419949

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

Small-scale laboratory experiments have been conducted to study the propagation of sound over a curved, rough, rigid, convex surface in the rangekR=275–550,andkε=0.09–0.18,wherekis the wave number,Rthe radius of curvature, and ε the characteristic roughness length scale of steep-sloped, densely packed scatterers. Experimental results are presented at 6, 8, and 12 kHz, with the receiver successively on the surface, along the line of sight behind the surface, and along a vertical axis in the shadow zone. At low frequencies (f=6 kHz,kε=0.09), a boundary wave caused by coherent multiple scattering develops near the surface, creeps into the deep shadow zone, and increases the sound-pressure levels measured in the deep shadow zone by up to 8 dB as compared to the levels measured in the absence of surface roughness. At high frequencies (f=12kHz,kε=0.18), surface roughness causes incoherent scattering and decreases the measured sound-pressure levels by about 10 dB on the surface, in the shadow zone, and by 10 to 20 dB along the line of sight behind the apex. It is shown that incoherent scattering occurs mostly in the bright zone, before the apex, whereas coherent scattering (boundary wave growth) occurs all along the surface, even in the deep shadow.

ISSN:0001-4966    

DOI:10.1121/1.419897

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

An inverse scattering method that uses eigenfunctions of the scattering operator is presented. This approach provides a unified framework that encompasses eigenfunction methods of focusing and quantitative image reconstruction in arbitrary media. Scattered acoustic fields are described using a compact, normal operator. The eigenfunctions of this operator are shown to correspond to the far-field patterns of source distributions that are directly proportional to the position-dependent contrast of a scattering object. Conversely, the eigenfunctions of the scattering operator specify incident-wave patterns that focus on these effective source distributions. These focusing properties are employed in a new inverse scattering method that represents unknown scattering media using products of numerically calculated fields of eigenfunctions. A regularized solution to the nonlinear inverse scattering problem is shown to result from combinations of these products, so that the products comprise a natural basis for efficient and accurate reconstructions of unknown inhomogeneities. The corresponding linearized problem is solved analytically, resulting in a simple formula for the low-pass-filtered scattering potential. The linear formula is analytically equivalent to known filtered-backpropagation formulas for Born inversion, and, at least in the case of small scattering objects, has advantages of computational simplicity and efficiency. A similarly efficient and simple formula is derived for the nonlinear problem in which the total acoustic pressure can be determined based on an estimate of the medium. Computational results illustrate focusing of eigenfunctions on discrete and distributed scattering media, quantitative imaging of inhomogeneous media using products of retransmitted eigenfunctions, inverse scattering in an inhomogeneous background medium, and reconstructions for data corrupted by noise.

ISSN:0001-4966    

DOI:10.1121/1.419898

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

A brief review is presented of a previously developed mean-square error method to solve the Neumann boundary-value problem corresponding to acoustic axisymmetric harmonic radiation and rigid body scattering from bodies of revolution of arbitrary shape. The method is based on the use of an internal line monopole source distribution along the axis. In contrast to earlier work, the pressures are simply expressed as line integrals of the source distributions which in the far field reduce to Fourier transform relationships. Exact expressions for the source strength distributions for a sphere are developed using the Fourier transform relationships. The source strength distributions involve spatial derivatives of Dirac delta functions and thus have a vanishingly small region of support about the center of the sphere. For cylindrically shaped bodies with large aspect ratios the spatial characteristics of the source strength distributions are shown to be more closely matched to the normal velocity distribution. The use of a discrete series of Dirac delta functions to represent the continuous line source distributions is presented for spherical radiation and scattering problems.

ISSN:0001-4966    

DOI:10.1121/1.419899

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

For transversely isotropic materials like fiber composites, but also unidirectionally grain-structured austenitic steels, the elastodynamic dyadic and triadic Green’s functions for the pure shear(SH)wave mode are given in the space–time domain. The first stage of the derivation is performed in a way similar to the derivation of these functions in the form of their 2D space–time spectral representations [M. Spies, J. Acoust. Soc. Am.96, 1144–1157 (1994)]. In the present study, the inverse Fourier integrations are performed using a far-field approximation. The resulting expressions appear in a coordinate-free form and contain the orientation of the material’s fiber axis as an additional parameter. Thus the results are particularly useful for extension to the case of layered material. Numerical evaluation is performed for a unidirectional composite material for several orientations. Since the application of theSH-wave type bears considerable potential in nondestructive testing, the results presented in this article may find some application within this framework.

ISSN:0001-4966    

DOI:10.1121/1.419900

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

An experimental investigation of the focusing of intense, airborne pressure pulses by an ellipsoidal reflector is reported. Short-durationNwaves were generated by weak sparks at the near focusF1of four different prolate ellipsoidal surfaces. Reflection then concentrated the rays at the far focusF2.Measurements were made with a wide-band microphone, primarily along the axis of the reflector. A few transverse measurements in the plane ofF2were also made. In the axial measurements the reflected (uprightNwave) and edge-diffracted (invertedNwave) components of the signal are distinct at points distant fromF2,approach each other as the focus is neared, and merge at the focus. At the focus the waveform isU-shaped, or cusped. BeyondF2a “droopy”Nwave emerges and, where the edge wave can be resolved, it now arrives first and is phase inverted relative to its prefocal version. The more intense reflected wave does not experience phase inversion. Some features of the observed waveforms are consistent with recent calculations by Hamilton, which are based on lossless, linear theory. Other wave characteristics, including pulse amplitude and location of the head and tail shocks, are strongly influenced by nonlinear effects.

ISSN:0001-4966    

DOI:10.1121/1.419950

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP