Investigation of the Rayleigh critical angle phenomenon for the characterization of surface properties

Rayleigh type acoustic critical angle experiments on a variety of samples ranging from single crystals to polycrystalline alloy and glasses have been performed. Two conclusions can be drawn from this work: (1) simple linear equations of motion, which include anisotropy, suffice for an approximate description of the observations; (2) certain observations at and near the critical angle, involving the production of anomalous harmonics, imply that the nonlinear characteristics of the water, and possibly the solid, cannot be ignored and need further study. Moreover, the new measuring apparatus, using an acoustic lens, has the following desirable features: (a) it allows local measurements of the solid properties to be made, and (b) except for problems associated with phase measurements of the reflected waves, experimental results are essentially consistent with the work of others who used a different experimental approach. We conclude that our goal of using a device in practical flaw imaging work is reasonable and holds promise of being a quantitative flaw imaging technique.