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ULTRASONIC BACKSCATTERING ENHANCEMENTS FOR TRUNCATED OBJECTS IN WATER: QUANTITATIVE MODELS, TESTS AND SPECIAL CASES


This survey is concerned with the scattering of sound in water by objects whose size significantly exceeds the acoustic wavelength. Diffraction from the edges of the object can be important for regions where reflected contributions are weak. Elastic contributions to the scattering, however, can be much larger in magnitude for certain viewing angles than simple edge diffraction. Such elastic contributions can greatly enhance the visibility of truncated cylinders imaged with a sonar. For situations where the dominant elastic contributions are the result of leaky waves excited on truncated objects, an approximation method has been developed. Leaky waves have phase velocities that exceed the speed of sound in water. Examples include Rayleigh waves on metallic objects, the symmetric generalization of Lamb waves on plates and shells, and (at sufficiently high frequencies) the lowest antisymmet- ric generalization of a Lamb wave. This type of scattering enhancement has been measured by us for metallic tilted bluntly truncated cylinders and cubes and glass disks. For most of these examples, the leaky wave is significantly attenuated upon traveling the length of the scatterer. As a consequence of that damping, the quality factor Q is small for the global modes associated with the reverberations of the leaky waves between truncations on the object. Consequently resonances associated with the global modes of the scatterer can be unimportant. In the case of shells, the leaky Lamb waves are sufficiently dispersive that frequency-dependent synchronization conditions must be met to facilitate strong coupling between the leaky waves and the incident acoustic field. largets fabricated from materials where either the shear wave velocity or both the shear and the longitudinal wave velocities are less than the speed of sound in water involve special considerations. Examples of such materials include rubbers and plastics in contrast to the metallic targets noted earlier. Significant backscattering enhancements associated with refracted waves and caustics have been .verified and modeled for tilted truncated plastic and rubber cylinders. Rayleigh waves on plastics have subsonic velocities relative to water and must be modeled differently than for the corresponding metallic target.......

【作者名称】: P. L. Marston, F. J. Blonigen, B. T. Hefner, K. Gipson, S. F. Morse
【作者单位】: Department of Physics, Washington State University Pullman, WA 99164-2814, USA
【关 键 词】: ULTRASONIC BACKSCATTERING ENHANCEMENTS FOR TRUNCATED OBJECTS IN WATER: QUANTITATIVE MODELS, TESTS AND SPECIAL CASES
【会议名称】: IUTAM Symposium on Diffraction and Scattering in Fluid Mechanics and Elasticity Jul 16-20, 2000 Manchester, United Kingdom
【期刊论文数据库】: [DBS_Articles_01]
【期刊论文编号】: 100,835,272
【摘要长度】: 2,298
【会议地点】: Manchester(GB)
【会议组织】: Department of Physics, Washington State University Pullman, WA 99164-2814, USA
【会议时间】: 2000
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