Wavefront expansions for pulse scattering by a surface inhomogeneity

Much recent interest has arisen in the coupled dynamics of fluid-solid interfaces, mainly with regard to the use of the acoustic microscope as a valuable technique for material characterisation and the detection of surface, and subsurface, flaws; there is also interest in structural acoustics and geophysical applications. The majority of recent work has dealt with time harmonic waves, in this paper solutions for transient disturbances are developed and analysed in detail.

The resulting fluid and solid responses are found in closed form allowing specific wavefronts to be identified and explicit results are given. Wavefront expansions for the head waves and cylindrical wave in the fluid are found explicitly, together with the disturbance generated by the leaky Rayleigh wave these are the dominant fluid responses detected experimentally and such exact solutions will be of value.

The limit of light fluid loading is examined separately; it is shown that the leading order fluid/ solid results are reconstructed by considering simpler problems where the fluid loading is taken to be absent. An unambiguous interpretation of the disturbance in the fluid created by the leaky Rayleigh wave is given in this light fluid loading limit.

Quarterly Journal of Mechanics and Applied Mathematics, 49, pp.657-674, 1996