Local Critical Angle Measurements for the Examination of Materials

Abstract

Interface waves excited on a liquid-solid boundary by an incident longitudinal sound wave in water can be used to examine physical properties near the surface of a solid. Focused longitudinal waves at an average angle of incidence equal to the Rayleigh critical angle excite interface waves locally on the boundary. approximately one shear wavelength into the solid and radiate a low amplitude longitudinal wave back into the water at an angle e. A point receiver may be used to record amplitude R(8) and phase +(e) of the radiated wave. Because R(8) and '+'(e) are modulated by local subsurface properties when e is equal to a critical angle, these properties may be imaged by scanning and recording R(O) and Y(E). Experimental results on local anisotropy and nonlinear materials response are presented. These waves penetrate