Abstract:

Leaky surface waves (such as Rayleigh waves) once launched on an elastic object will undergo partial reflection at the truncations of the object. Under certain conditions, such reflections can radiate locally flat acoustic wavefronts with a reversal of the acoustic-wave vector, and thus a large backscattered signal is produced. In the present experiments, a solid stainless-steel cylinder was ensonified through an angular region, which included the conditions for launching meridional and helical Rayleigh waves, and the resulting backscattering enhancements are consistent with hypothesized reflection processes. For the enhancement associated with a meridional ray, the observed peak magnitude of the retroreflected signal is in general agreement with approximate theoretical predictions from a convolution formulation [P. L. Marston, J. Acoust. Soc. Am. 102, 358--369 (1997)]. Helical ray contributions are also observed, but these are generally weaker at ultrasonic frequencies.