摘要:

Abstract not available.

ISSN:0001-4966    

DOI:10.1121/1.418259

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

Abstract not available.

ISSN:0001-4966    

DOI:10.1121/1.418261

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:10.1121/1.418215

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

The development of a smart foam for passive–active noise control is discussed. The smart foam consists of cylindrically curved sections of PVDF film embedded in partially reticulated polyurethane acoustic foam forming a very thin, compact arrangement. The device is designed to reduce sound by the simultaneous action of the passive absorption of the foam (effective at high frequencies) and the active input of the PVDF element driven by an oscillating electrical input (effective at low frequencies). The PVDF actuator is configured to behave in a linear sense and to couple in-plane strain associated with piezoelectric effect with out-of-plane motion needed to radiate sound from the foam surface. The performance of the passive–active device is studied for controlling sound radiation from a vibrating piston. A feedforward LMS controller is used to minimize the signal from a far-field error microphone. Results of harmonic and broadband control are presented. The potential of the smart foam for globally reducing sound radiation in the low- and high-frequency range is demonstrated.

ISSN:0001-4966    

DOI:10.1121/1.418234

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

The basic concepts and underlying assumptions of Statistical Energy Analysis (SEA) are reviewed. Using coupled simple oscillators as models for resonant modes, power balance equations are derived. Equipartition of energy among modes within a subsystem, and strong versus weak coupling between subsystems are discussed. Input requirements for exercising SEA power balance equations are defined and methods of obtaining the required input are outlined. Examples of the applications of SEA are presented and discussed.

ISSN:0001-4966    

DOI:10.1121/1.418074

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

An efficient and reliable numerical scheme is developed to compute the radiation directivity and total power radiated by isolated eigenmodes and by finite bandwidth excitations of a membrane of arbitrary shape over the whole frequency domain. Results are presented for the case of a membrane having the shape of a stadium, this shape having been studied intensively in the literature concerned with the correspondence between classical geometrical ray trajectories and high-frequency vibrations, the so-called “quantum chaos” problem. Localization of the radiation directivity is shown to be due to “scars” of eigenmodes made by resonance on periodic ray orbits. The dependence of the radiation efficiency as a function of the ratiocM/cof the membrane wave velocitycMover the air sound speedcand its important fluctuations from mode-to-mode is explained by the theory of random matrices.

ISSN:0001-4966    

DOI:10.1121/1.418218

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

A method is presented for the analysis of the space-time domain acoustic wave field in a continuously layered, lossy, isotropic fluid or equivalent fluid. Application of vertically varying compliance and inertia memory functions enables the modeling of a large class of depth-dependent loss properties. The method is based on integral transformations and consists of three steps. First, a temporal Laplace transformation with a real and positive transform parameter is applied, which is followed by horizontal spatial Fourier transformations. Second, higher-order, WKBJ-like asymptotic representations are derived that form approximate solutions of the resulting transform domain problem. With the chosen forward transformation process, problems caused by a zero vertical slowness are avoided, and the need for more intricate types of asymptotics is absent. Third, the Cagniard–De Hoop method is employed for the transformation back to the space-time domain. The form of the transform domain expressions allows for a very efficient use of the inversion process, while many steps of the inverse transformation may be performed analytically. Since the method does not impose a numerical limit on the bandwidth of the result, it may also be employed to generate a Green’s function. Numerical results are presented for reflections from half-spaces filled with a continuously layered, equivalent fluid with depth-dependent losses. At each level these losses show an almost “constant-Q” behavior in the frequency domain. The results show that there is an interval, beginning with the arrival time, on which the improvement due to the use of higher-order asymptotics is significant.

ISSN:0001-4966    

DOI:10.1121/1.418219

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

The Biot–Tolstoy exact time-domain solution for the three-dimensional impulse response of an impenetrable wedge is extended to accommodate the isovelocity or density-contrast wedge. Fourier transformation of the time and axial variables, along with a Kantorovich–Lebedev transform applied to the cylindrical radial coordinate, leads to a solution in terms of residue series. When the wedge angle is a rational fraction of π, the residue series can be reduced to a finite sum which is evaluated for some special cases. The total pressure field consists of geometrical acoustics contributions, as predicted by Snell’s laws, plus a modified version of the Biot–Tolstoy diffraction field.

ISSN:0001-4966    

DOI:10.1121/1.418220

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

Solid rods are submerged in a water tank and illuminated by an ultrasonic source transducer. Along the water surface, transducers are used to measure the propagating wave fields. Even for only three rods, the scattered wave field is very complex. Although the major events can be readily interpreted as direct reflections, the remaining wave field consists of complicated interactions of the wave fields with the scatterers and the water surface. To aid the interpretation, the experiment is modeled numerically using the multiple multipoles method which decomposes the wave fields by their respective origins. Hence, particular events can be correlated with particular scatterers as well as with particular paths of propagation. The numerical method has already been used as a versatile tool to model acoustic or elastic multiple-scattering problems where homogeneous scatterers were embedded in a homogeneous full space. In the present paper, the scheme is expanded to multiple scattering between solids submerged in a fluid. For each scatterer, the waves induced in the fluid are expressed by sets of multipole solutions with different origins. Thus by construction, the scattered wave fields are decomposed by scatterer. The numerical solutions match the ultrasonic experiments very well. Furthermore, the different events can be identified as reflections, internal multiples, or diffractions through the solid rods.

ISSN:0001-4966    

DOI:10.1121/1.418221

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

Tissue speed of sound inhomogeneities cause significant degradation of medical ultrasound images. In certain cases these inhomogeneities can be modeled as a thin, spatially varying time delay screen located at the face of the transducer. Correction of such aberrators requires the addition of compensating time delays to the normal system focusing delays. These compensating delays are estimated from the arrival time differences between echoes received on different array elements. The accuracy with which these arrival time differences can be estimated is limited by the level of correlation between received speckle signals. This paper derives analytical expressions predicting the correlation between speckle signals acquired by a pulse echo system with either point or larger receive elements in the presence of near-field phase aberrations. Simulations are presented which are in good agreement with theoretical predictions. Similarities between the derived expressions and the Van Cittert–Zernike Theorem are discussed. These results indicate that near-field phase aberration correction may be far more difficult than previous analyses suggest because of the low correlation between echoes received by adjacent elements in elevation in 1.5-D arrays. Transmit aperture amplitude apodization and a new translating aperture technique are presented as methods for improving speckle correlation.

ISSN:0001-4966    

DOI:10.1121/1.418235

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP