摘要:

Abstract not available.

ISSN:0001-4966    

DOI:10.1121/1.421308

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

摘要:

Abstract not available.

ISSN:0001-4966    

DOI:10.1121/1.421307

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

ISSN:0001-4966    

DOI:10.1121/1.421371

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:10.1121/1.421311

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

摘要:

The potential for functional and underlying physiological change in the adult auditory system is examined through review and evaluation of several sets of literature including auditory deprivation and recovery, auditory learning after hearing aid fitting, auditory abilities of normal listeners exposed to masking noise, and neural plasticity in the sensory and motor systems of animals. This tutorial review is meant for the reader who may be interested in auditory learning and who would like to have a summary and evaluation of the various findings to date. The focus of the review is the effect that various findings of auditory learning may have on hearing aid fitting and selection.

ISSN:0001-4966    

DOI:10.1121/1.421050

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

摘要:

Backward projection schemes use data in front of a transmitter to reconstruct a field at closer points. Existing techniques have concentrated propagating radial and temporal information along constant planar cross sections in front of a planar source. This approach requires a careful consideration of evanescent waves, as the transfer function used to backproject in space causes evanescent wave solutions to increase exponentially with the projected distance. Erroneous signals may result from exponentially increasing noise, experimental error or roundoff error. A method is presented that is designed to work with imaging methods that record three-dimensional spatial data at constant times. Several widely used optical methods are of this type. Our algorithm projects the field backward in time via linear wave theory. The approach is similar to previously reported methods but is designed to work with time-constant data and avoids problems associated with evanescent waves.

ISSN:0001-4966    

DOI:10.1121/1.421051

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

摘要:

This paper presents an analytical study of elastodynamic waves propagating along an arbitrary direction in anisotropic materials with tetragonal symmetry. Upper and lower bounds are developed on the wave speeds through an additive decomposition of the acoustic tensor into an associated hexagonal counterpart and a rank-one modification, the eigenproperties of which can be determined analytically. The bounds are obtained by applying the minimax property of eigenvalues. Linear approximations of the wave speeds are obtained from a first-order expansion of the eigenvalues of the acoustic tensor, with respect to a tetragonality index, about the value of that index for which tetragonal symmetry degenerates to hexagonal symmetry. A numerical example shows that the linear approximations agree remarkably well with the exact values of the wave speeds.

ISSN:0001-4966    

DOI:10.1121/1.421368

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

摘要:

Acoustic holography is one of the best methods to visualize sound fields. The quality of the visualized sound is primarily determined by the size of the hologram, its microphone spacing, and the number of microphones. This paper describes a way to virtually increase the hologram size and the spatial resolution of the holograph. For a stationary sound field, the method continuously sweeps the sound field by a line array of microphones. For moving sound sources, radiating sound is measured by using a line array of microphones fixed in space. In both cases, the measured signals have Doppler effects. The theoretical formulation has been systematically addressed by employing a moving coordinate which has relative motion between the measurement coordinate and the hologram coordinate. Simulations and experiments support the proposed theory. The drawback is that the method is only applicable to discrete frequencies.

ISSN:0001-4966    

DOI:10.1121/1.421375

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

摘要:

Acoustic transient Bessel beams (TBB) are a new class of waves which maintain their peak amplitude and general shape as they propagate in free space from an infinite planar aperture. The on axis and far field space-time properties of acoustic TBB waves generated by a finite spatial aperture are investigated using impulse response methods. The on-axis transition from the near field to the far field is investigated and several analogies to the acoustic field generated from a circular piston source are observed. In particular, the importance of an edge generated wave in determining the transition for the TBB field is clearly noted. Space-time properties of the far field are also investigated as a function of polar angle using impulse response methods. Numerical results are presented to illustrate the general characteristics of the on-axis and far field impulse response for a finite aperture.

ISSN:0001-4966    

DOI:10.1121/1.421329

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

摘要:

Coupled modes theory, as applied to 2-D wave propagation in range-dependent isotropic elastic waveguides in curvilinear orthogonal coordinates, is proposed. The model consists of one or more curvilinear layers with interfaces and outer boundaries departing slowly from the coordinate surfaces. The material parameters are supposed to be slowly dependent on the longitudinal coordinate. Four-dimensional vector-valued functions with the displacements, rotation, and divergence as the components are shown to be a convenient form of wave field description to extend the coupled modes theory from liquid to elastic waveguides. For this case, the cross section operator is defined and the generalized bi-orthogonality property of its eigenfunctions is established. Using the generalized bi-orthogonality, the coupling equations are derived. Wave propagation in a tube which narrows slowly to a conic rod and in a disk of radially dependent thickness are considered as the examples. The differences between the results obtained by the coupled modes theory and those the multiple-scales theory leads to are discussed. The theory modification for dealing with a cutoff phenomenon and the general algorithm of computation of the wave field excited by a point source are considered.

ISSN:0001-4966    

DOI:10.1121/1.421330

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP