Direct Measurement of Rayleigh Wave Velocity by Schlieren Visualization and Estimates of Shear Velocity Therefrom

Schlieren visualization experiments are used to obtain direct, accurate measurements of Rayleigh phase velocity on various materials. Illumination of a plane solid surface underwater at the Rayleigh angle produces an easily identifiable null strip in the radiation which uniquely defines the Rayleigh angle. This strip is caused by the mutual cancellation of equal amplitude specular and Rayleigh radiations, which are 180°out of phase at the Rayleigh angle. Rayleigh velocities are calculated from the measured angle by a simple equation. The measured Rayleigh velocities are used to give estimates of shear velocity, and these estimates are compared with direct shear velocity measurements. Attenuation of the Rayleigh wave in the low megahertz region is given for six materials, and shown to agree with theoretical predictions.