Analysis of the Wedge Method of Generating Guided Waves

The “wedge” method of generating guided waves in isotropic layers was analyzed both theoretically and experimentally by Viktorov et. al, in 1965 [1]. The main parts of the work were later reproduced in Viktorov’s now famous book on Rayleigh and Lamb waves [2]. Of several detailed observations made in these investigations, one was that: For optimal generation of a mode of a given wavenumber, k, the angle of the wedge should be “in the neighborhood” of the Snell’s law angle, θ i = sin−1(k/k w), where k w represents the wavenumber of the wave in the wedge[2]. Such a choice of incident angle was being used by experimentalists utilizing Lamb waves for nondestructive evaluation purposes [3–5] even before Viktorov’s analysis. The use of such an angle no doubt arose from the theory of (infinite) plane wave reflection/refraction at planar interfaces. In those cases, which are strictly of academic interest or for approximating real experimental conditions, Snell’s law holds exactly as a result of satisfaction of boundary conditions along the entire (infinite) interface.