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Comparison of Radiation and Scattering Mechanisms for Objects Having Rayleigh Wave Velocities Greater than or Smaller Than the Speed of Sound in the Surrounding Water

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Metallic objects typically have material properties such that the characteristic Rayleigh wave velocity exceeds the speed of sound in water. As a consequence, over a wide range of frequencies, smooth objects including empty shells support surface guided waves having phase velocities exceeding the speed of sound in water. Such waves are effective in leaking radiation and give rise to various backscattering enhancements not necessarily associated with global resonances of the object. For example, high frequency meridional ray backscattering enhancements have been observed and modeled for tilted metallic solid cylinders K. Gipson, Ph.D. Thesis, WSU 1998 and shells S. F. Morse, et al., J. Acoust. Soc. Am 103, 785-794 1998. For plastic polymer objects, however, it is necessary to reexamine the significant radiation and scattering mechanisms because the intrinsic Rayleigh phase velocity is smaller than the speed of sound in water. Some novel scattering enhancement mechanisms for such objects are introduced including the caustic merging transition for waves transmitted through tilted cylinders and the tunneling to subsonic Rayleigh waves. The former has an optical analogy in the scattering of light by tilted dielectric fibers C. M. Mount, D. B. Thiessen, and P. L. Marston, Appl. Opt. 37, 1534-1539 1998 and has been observed in sound scattered by tilted truncated polystyrene cylinders F. J. Blonigen and P. L. Marston, J. Acoust. Soc. Am. 102, 3088 A 1997. Work supported by the Office of Naval Research.

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  • Acoustics

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