摘要:

A common procedure for estimating the apparent width of a ray in volume propagation is to construct the locus of defective paths having a phase shift that deviates from that of the true ray by π radians [Yu A. Kravtsov and Yu I. Orlov, Sov. Phys. Uspekhi23, 750–760 (1980); P. L. Marston, Phys. Acoust.21, 1–234 (1992)]. An analogous construction is described for the effective surface region for the high‐frequency coupling of sound with a leaky wave on a curved surface along a given ray. Results are shown for right circular cylinders and spheres. For defective paths in the plane of incidence of the ray, the resulting Fresnel angular half‐width of the patch is approximately [2π/(ka cos θl)]1/2radians whereais the radius of the surface, sin θl=c/clandclis the leaky wave phase velocity. The analysis is relevant to estimating the degree to which ray coupling processes can be considered to be local processes. It is also relevant to the anticipation of the transition to creeping wave behavior whenclbecomes sufficiently small for the Fresnel region to touch the edge of the scatterer. Defective paths outside the plane of incidence are also considered for a right circular cylinder. The Fresnel patch associated with a leaky ray to (or from) a specified point on the cylinder is approximately elliptical and the analysis is relevant to radiation as well as to scattering.

ISSN:0001-4966    

DOI:10.1121/1.410202

出版商:Acoustical Society of America    

年代:1994

数据来源: AIP

摘要:

The problem of a plane wave obliquely incident from a homogeneous ideal fluid upon a random fluid layer is considered and expressions are derived for the diffusely backscattered intensity. The thin layer is taken to have properties that vary only in the two in‐plane directions. A first Born approximation is used and the average intensity of the incoherent part of the backscattered wave is found to be proportional to the two‐dimensional spatial Fourier transform of the auto‐ and cross‐covariance functions of the layer. Within the confines of the validity of the first Born approximation, therefore, the inverse scattering problem may be straightforward, provided the necessary experimental data of the incoherent wave can be obtained. A sufficient condition to estimate the range in which the second‐order term in the Born series can be neglected is also given.

ISSN:0001-4966    

DOI:10.1121/1.410203

出版商:Acoustical Society of America    

年代:1994

数据来源: AIP

摘要:

Many hearing aid users complain about a reduced intelligibility of speech in noisy environments. Directional systems are a successful approach for noise reductions in hearing aids. These systems transmit signals from acoustic sources lying in front of the hearing aid user while suppressing signals from other directions, which are assumed to be noise. Several methods are known to obtain directivity. One is to use directional microphones, another is digital postprocessing of several microphone signals. In this letter, the combination of directional microphones with the adaptive beamformer, a directional signal processing approach, is discussed. Intelligibility tests with both normal‐hearing and hearing‐impaired subjects are presented. It is shown that the combination of directional microphones with digital postprocessing is able to improve the intelligibility of speech in a noisy environment significantly, when compared to any one of these two approaches by itself.

ISSN:0001-4966    

DOI:10.1121/1.410204

出版商:Acoustical Society of America    

年代:1994

数据来源: AIP

摘要:

A study of published literature and information from piezoelectric ceramic vendors and underwater sound transducer designers has been undertaken to establish mechanical and electrical operating limits for transducers. It appears that operation up to 3.9–5.9 kV/cm (10–15 V/mil) rms and 69–103 MPa (10–15 kpsi) peak compression is achievable in practical sonar transducers.

ISSN:0001-4966    

DOI:10.1121/1.410205

出版商:Acoustical Society of America    

年代:1994

数据来源: AIP

摘要:

The adiabatic‐mode solution is widely used for modeling sound propagation in slowly varying ocean environments. However, there are several variations of adiabatic mode solutions and there has been confusion about which form is correct. The standard derivation yields a form that isnotreciprocal. As such, it has often been modified in anadhocfashion to produce a form that is reciprocal. This lack of reciprocity is due to the common assumption that the environment is rotationally symmetric about the source. By assuming instead a plane‐geometry environment a new adiabatic form that is reciprocal is derived.

ISSN:0001-4966    

DOI:10.1121/1.410206

出版商:Acoustical Society of America    

年代:1994

数据来源: AIP

ISSN:0001-4966    

DOI:10.1121/1.411433

出版商:Acoustical Society of America    

年代:1994

数据来源: AIP

ISSN:0001-4966    

DOI:10.1121/1.411312

出版商:Acoustical Society of America    

年代:1994

数据来源: AIP

ISSN:0001-4966    

DOI:10.1121/1.410207

出版商:Acoustical Society of America    

年代:1994

数据来源: AIP

ISSN:0001-4966    

DOI:10.1121/1.410208

出版商:Acoustical Society of America    

年代:1994

数据来源: AIP

ISSN:0001-4966    

DOI:10.1121/1.410210

出版商:Acoustical Society of America    

年代:1994

数据来源: AIP