Excitation of surface waves of different modes at fluid–porous solid interface

The presence of ultrasonic surface waves of various modes on a fluid–porous solid interface is demonstrated and their velocities measured. The experimental technique (developed earlier by one of the authors for a fluid–isotropic solid interface) utilizes reflected broadband spectra from periodic surfaces. Three sharp minima corresponding to three mode-converted waves coupled to the porous solid are observed. The velocities of these ‘‘surface’’ waves are in qualitative agreement with theoretical predictions [S. Feng and D. L. Johnson, J. Acoust. Soc. Am. 74, 906 (1983) and 74, 915 (1983)] and are identified as pseudo Rayleigh, pseudo Stoneley, and true Stoneley waves.