Backscattering enhancement from leaky Rayleigh waves on the flat end of a tilted solid cylinder: Observations and Gaussian beam model

Abstract

The circular end of a tilted solid cylinder in water was illuminated by high frequency sound. When the angle of incidence was close to the Rayleigh wave coupling angle, a leaky Rayleigh wave was launched which reflects from the rim. The reflected wave passes through a focus which lies on a diameter of the cylinder, and a significantly attenuated leaky wave subsequently reflects back along the diameter from the opposite rim. The radiation from the focused initial reflection was observed to produce a large backscattering enhancement having a far-field amplitude significantly greater than for reflection from a rigid sphere having the same diameter as the cylinder [K. Gipson, Ph.D. thesis, Wash. State Univ. (1998)]. This enhancement was modeled by approximating the leaky wave as a focused Gaussian beam and approximating the initial surface and far-field amplitudes using a variation of a method previously described [P. L. Marston, J. Acoust. Soc. Am. 102, 1628–1638 (1997)]. One of the principal curvatures of the outgoing wavefront vanishes so the enhancement is associated with a far-field caustic. The theory should be applicable to other flat circular targets. [Work supported by the Office of Naval Research.]