Ultrasonic Surface and Bulk Wave Interaction with Fluid-Saturated Porous Solids

Mayes, M.
Nagy, P.
Adler, L.
Bonner, B.
Streit, R.
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There has recently been considerable interest in the acoustics of fluid-saturated porous media. The most interesting peculiarity, the existence of two compressional waves, was first predicted by Biot [1] in 1956. It was not until 1980 that Plona [2] experimentally observed the additional slow compressional bulk wave in a water-saturated porous solid composed of sintered glass spheres. Even more recently, Feng and Johnson [3] have extended the Biot theory to numerically predict the velocities of a new surface mode as well as the expected pseudo Rayleigh and pseudo Stoneley modes at fluid-porous solid (i. e. fluid/fluid-saturated porous solid) interface. The expected modes are either below the fluid velocity, so that energy will not leak into the fluid at all, or just above it so that energy leaks at such a high angle, in which case simple phase-matching techniques are not applicable for excitation and detection. In a recent paper [4], the authors suggested the application of a slightly corrugated periodic surface, since, in this case every surface mode becomes somewhat “leaky” in certain directions at particular resonant frequencies. In this work we are presenting experimental results of surface wave velocity measurements, using this periodic surface technique. The surface wave velocities are compared to bulk results obtained by a new wedge technique.