Backscattering enhancements due to retroreflection of ultrasonic leaky Rayleigh waves at corners of solid elastic cubes in water

Backscattering enhancements can be important for interpreting acoustical im ages of scatterers. Experiments were performed on a solid stainless steel c ube in water in order to investigate a significant mechanism for producing a large backscattered signal. Enhanced high-frequency backscattering is obs erved when the block is rotated such that the incident acoustic wave strike s one of its flat surfaces in the vicinity of the coupling angle for launch ing a leaky Rayleigh wave at the steel-water interface. This enhancement ca n be explained as a retroreflection of the leaky wave at a corner of the bl ock, which results in a reversal of the incident wave vector and thus produ ces a large backscattered signal. The magnitude of the peak backscattered p ressure is approximated using a convolution formulation [P. L. Marston, J. Acoust. Soc. Am. 97, 34-41 (1995)], Observed backscattering enhancements su pport the validity of the convolution formulation to approximate the genera l magnitude of the peak pressure, as well as being consistent with the deph asing predicted by that theory as the block is rotated away from the coupli ng angle. Tilting the block while maintaining the coupling angle reduces th e backscattered amplitude because of changes in the reflection coefficients at the corner as well as increased attenuation. (C) 1999 Acoustical Societ y of America. [S0001-4966(99)03002-7].