摘要:

Abstract not available.

ISSN:0001-4966    

DOI:10.1121/1.418257

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:10.1121/1.418427

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

ISSN:0001-4966    

DOI:10.1121/1.419505

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

ISSN:0001-4966    

DOI:10.1121/1.418310

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

Microcalcifications are small crystals of calcium apatites which form in human tissue through a number of mechanisms. The size, morphology, and distribution of microcalcifications are important indicators in the mammographic screening for and diagnosis of various carcinomas in the breast. Although x-ray mammography is currently the only accepted method for detecting microcalcifications, its efficacy in this regard can be reduced in the presence of dense parenchyma. Current ultrasound scanners do not reliably detect microcalcifications in the size range of clinical interest. The results of theoretical, simulation, and experimental studies focused on the improvement of the ultrasonic visualization of microcalcifications are presented. Methods for estimating the changes in microcalcification detection performance which result from changes in aperture geometry or the presence of an aberrator are presented. An analysis of the relative efficacy of spatial compounding and synthetic receive aperture geometries in the detection of microcalcifications is described. The impact of log compression of the detected image on visualization is discussed. Registered high resolution ultrasound and digital spot mammography images of microcalcifications in excised breast carcinoma tissue and results from the imaging of suspected microcalcificationsin vivoare presented.

ISSN:0001-4966    

DOI:10.1121/1.417973

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

The effect of specific cavity dimensions of circular concentric Helmholtz resonators is investigated theoretically, computationally, and experimentally. Three analytical models are employed in this study: (1) A two-dimensional model developed to account for the nonplanar wave propagation in both the neck and the cavity; (2) a one-dimensional solution developed for the limit of small cavity length-to-diameter ratio,l/d, representing a radial propagation in the cavity; and (3) a one-dimensional closed-form solution for configurations with largel/dratios which considers purely axial wave propagation in the neck and the cavity. For low and highl/d, the resonance frequencies determined from the two-dimensional approach are shown to match the one-dimensional predictions. For cavity volumes withl/d>0.1, the resonance frequencies predicted by combining Ingard’s end correction with one-dimensional axial wave propagation are also shown to agree closely with the results of the two-dimensional model. The results from the analytical methods are then compared with the numerical predictions from a three-dimensional boundary element method and with experiments. Finally, these approaches are employed to determine the wave suppression performance of circular Helmholtz resonators in the frequency domain.

ISSN:0001-4966    

DOI:10.1121/1.417986

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

Propagation and diffraction of time-harmonic elastic body waves through homogeneous and isotropic materials is revisited. The two-component representation of body waves is given which is applicable in the high- and intermediate-frequency regimes when the family of rays is (i) regular or (ii) possesses an irregularity due to the presence of a wedge, an acoustic point source located on the boundary, simple caustic, or focal line. Both physical and mathematical description of the phenomena under consideration is offered. The resulting expressions are asymptotic in character and easy to compute. They should prove useful in producing algorithms for describing acoustic fields in homogeneous and isotropic materials with isolated defects and in providing benchmark cases for testing numerical codes designed to solve elastic wave equations in more complicated situations.

ISSN:0001-4966    

DOI:10.1121/1.417970

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

The general theory of a ray-mode approach for time-harmonic responses and a wavefront-resonant approach for transient responses of submerged structures [I-T. Lu, J. Acoust. Soc. Am.99, 114–132 (1996)] is applied to a prototype structure consisting of a cylindrical pipe, hemispherical endcaps, a bulkhead, and a rib. The acoustic scattering returns are synthesized systematically in terms of angular spectra of surface modes of the structural elements where bookkeeping of various spectral objects such as ray, collective ray, modes, ray mode, resonance, etc. can be maintained. Ray shooting and eigenray searching procedures for the guided modes of structural elements are derived. An approximate solution for the resonances of the global submerged structure is also obtained. Numerical examples of typical ray trajectories of these guided modes, travel times of wavefronts, and complex frequencies of resonances are presented.

ISSN:0001-4966    

DOI:10.1121/1.417966

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

Diffraction tomography is an imaging technique applicable to crosshole seismic data and aimed at achieving optimal spatial resolution away from the borehole. In principle the method can form acoustic images equivalent to extending acoustic well logs away from the wellbore and into the formation with a spatial resolution less than one wavelength of the radiation employed to gather the crosshole data. This paper reports on the capability of diffraction tomography to produce high-resolution reconstructions of simple targets from limited-view-angle data. The goal is to quantify the resolution and velocity-reconstruction capability of diffraction tomography with realistic source–receiver geometries. Simple targets (disks and low-contrast sequences of layers) are used for this study. The scattering from these targets can be calculated without approximation, making them ideal test cases for the algorithm. The resolution capability of diffraction tomography is determined to be on the order of one wavelength for several experimental geometries. It is shown that the image-formation characteristics of diffraction tomography, in terms of its ability to determine object boundaries and velocities, are closely related to the experimental geometry. Reflection and vertical seismic profiling (VSP) experiments tend to reproduce boundaries well, while crosshole experiments give the best overall reconstruction of both target boundaries and velocity. The quantitative accuracy of the velocity reconstruction depends upon the match between the spatial-frequency content of the object and the spatial-frequency response of the algorithm. For some targets, the velocity cannot be correctly reproduced from limited-view-angle data.

ISSN:0001-4966    

DOI:10.1121/1.417967

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

The importance of expanding Green’s functions, particularly free-space Green’s functions, in terms of orthogonal wave functions is practically self-evident when frequency domain scattering problems are of interest. With the relatively recent and widespread interest in time domain scattering problems, similar expansions of Green’s functions are expected to be useful in the time domain. In this paper, two alternative expressions, expanded in terms of orthogonal spherical wave functions, for the free-space time domain scalar Green’s functions are presented. Although the two expressions are equivalent, one of them is seen to be more convenient for the calculation of the scattered field for a known equivalent source density, whereas the second expression is more suitable for setting up an integral equation for the equivalent source density. Such an integral equation may be setup, for example, by the application of a time domain equivalent of the T-matrix (extended boundary condition) method.

ISSN:0001-4966    

DOI:10.1121/1.417968

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP