The V-Groove lens

Abstract

Primarily designed for imaging purposes, the acoustic microscope finds application in the qualitative evaluation of materials, too. The lens response as a function of defocus, which is known as the V{z) curve, is formed by the interference of various wave components reflected from the material surface. Leaky wave velocities of the material can be extracted from this interference pattern. The accuracy of the measurement is heavily influenced by the leaky wave contribution to the V(z) curve. Hence, lens geometries capable of efficiently exciting leaky wave modes need to be designed. If a particular geometry is to be used for measurements on materials exhibiting crystalographic anisotropies, it must be able to couple to modes only in a single direction, as well. The proposed V-Groove lens, combines the directional sensitivity of the Line Focus Beam lens and the efficiency of the Lamb Wave lens. The geometry is able to accurately measure the direction dependent leaky wave velocities of anisotropic materials. A new model based approach improves the accuarcy of the extracted velocities. In this study, the V-Groove lens has been analyzed theoretically. A mathematical model describing the lens response has been developed. The performance of the V-Groove lens has been tested by simulations. A new leaky wave velocity extraction algorithm based on fitting the model curve to actual curves using Nelder-Meade search has been proposed. A prototype lens has been manufactured and performance figures have been verified experimentally. The accuracy of the lens has been compared with those of other various geometries.