Leaky waves on curved scatterers. I. Fresnel width of coupling regions and elliptical Fresnel patches
作者:
Philip L. Marston,
期刊:
The Journal of the Acoustical Society of America
(AIP Available online 1994)
卷期:
Volume 96,
issue 3
页码: 1893-1898
ISSN:0001-4966
年代: 1994
DOI:10.1121/1.410202
出版商: Acoustical Society of America
关键词: GEOMETRICAL ACOUSTICS;SCATTERING;SOUND WAVES;CYLINDERS;SPHERES
数据来源: AIP
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.
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