摘要:

Abstract not available.

ISSN:0001-4966    

DOI:10.1121/1.423993

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

ISSN:0001-4966    

DOI:10.1121/1.423267

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

ISSN:0001-4966    

DOI:10.1121/1.423996

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

ISSN:0001-4966    

DOI:10.1121/1.424000

出版商:Acoustical Society of America    

年代:1998

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:10.1121/1.423272

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

摘要:

Reticulated vitreous carbon has been successfully used as a stack material in thermoacoustic prime movers and refrigerators. It is a rigid glassy carbon material, with a porous spongelike structure. Test results indicate peak pressure amplitudes of up to 32% in a prime mover, and refrigeration performance comparable to that of a traditional plastic roll stack.

ISSN:0001-4966    

DOI:10.1121/1.424055

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

摘要:

Distinct frequency dependencies of the acoustic backscattering by zooplankton of different anatomical groups have been observed in our previous studies [, ICES J. Mar. Sci.49, 97–106 (1992); Stanton et al., ICES J. Mar. Sci.51, 505–512 (1994)]. Based mainly on the spectral information, scattering models have been proposed to describe the backscattering mechanisms of different zooplankton groups [, J. Acoust. Soc. Am.103, 236–253 (1998b)]. In this paper, an in-depth study of pulse compression (PC) techniques is presented to characterize the temporal, spectral, and statistical signatures of the acoustic backscattering by zooplankton of different gross anatomical classes. Data collected from various sources are analyzed and the results are consistent with our acoustic models. From compressed pulse (CP) outputs for all three different zooplankton groups, two major arrivals from different parts of the animal body can be identified: a primary and a secondary arrival. (1) Shrimplike animals (Euphausiidsand decapod shrimp; near broadside incidence only): the primary one is from the front interface (interface closest to the transducer) of the animal and the secondary arrival is from the back interface; (2) gas-bearing animals (Siphonophores): the primary arrival is from the gas inclusion and the secondary arrival is from the body tissue (“local acoustic center of mass”); and (3) elastic shelled animals (Gastropods): the primary one is from the front interface and the secondary arrival corresponds to the subsonic Lamb wave that circumnavigates the surface of the shell. Statistical analysis of these arrivals is used to successfully infer the size of the individual animals. In conjunction with different aspects of PC techniques explored in this paper, a concept of partial wave target strength (PWTS) is introduced to describe scattering by the different CP highlights. Furthermore, temporal gating of the CP output allows rejection of unwanted signals, improves the output signal-to-noise ratio (SNR) of the spectra of selected partial waves of interest, and provides a better understanding of the scattering mechanism of the animals. In addition, it is found that the averaged PWTS can be used to obtain a more quantitative scattering characterization for certain animals such as siphonophores.

ISSN:0001-4966    

DOI:10.1121/1.424056

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

摘要:

The propagation of acoustic or ultrasonic pulses and waves in 1-D media with continuous inhomogeneities due to spatial variations in density, Young modulus, and/or cross section of the propagation medium is discussed. A semianalytical approach leads to a general form of the solution, which can be described by a function, whose Taylor expansion is absolutely convergent. The special case of a periodic inhomogeneity is studied in detail and the dispersion law is found. It is also shown that a finite width pulse is generally not broken down by the inhomogeneity, even though its law of motion is perturbed. A numerical treatment based on the Local Interaction Simulation Approach (LISA) is also considered, and the results of the simulations compared with the semianalytical ones.

ISSN:0001-4966    

DOI:10.1121/1.423283

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

摘要:

The propagation of acoustic waves in immersed waveguides has been previously studied with the help of the finite element method, using theATILAcode [A. C. Hladky-Hennion et al., J. Sound Vib.200, 519–530 (1997)]. But this method, which is a modal analysis, essentially concerns the case of rectilinear, infinite, and uniform waveguides. Thus this paper deals with another way of solving the problem of wave propagation along waveguides, with the help of a time analysis using finite elements. First, the theoretical formulation is presented for immersed structures. Then, Plexiglas and brass wedge guides, of different apex angles, are considered. When immersed in water, these wedges generate either propagating or radiating wedge waves. The finite element results, using a time analysis, are compared to the previous finite element results, using a modal analysis and to the experiments, leading to a good agreement. Thus the approach can be easily extended to other waveguides whatever their cross sections.

ISSN:0001-4966    

DOI:10.1121/1.423284

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

摘要:

The far-field directivity pattern can be computed using the fast Fourier transform (FFT) algorithm. Numerical implementation of the angular spectrum approach (ASA) is generally used to compute the pressure field. The aim of this paper is to demonstrate that the discrete far-field pressure can be only computed by the calculation of the DFT of the normal velocity. In fact, using the asymptotic expression of the Rayleigh’s integral, which is also the solution of Helmholtz equation, it will be shown that the analytical far-field pressure is given by the Fourier transform of the normal velocity. Guidelines for the selection of sampling interval and the size of the baffle in which the source is mounted will be given. Then this paper shows that the size of baffle influences the angular resolution at which the far field is computed and when the source is oversampled the computed discrete pressure becomes better. Numerical results concerning a transducer that exhibits harmonic oscillations will be considered and discussed.

ISSN:0001-4966    

DOI:10.1121/1.423305

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP