A modified ray theory for predicting the V(x,z) response of a point-focus acoustic microscope in the presence of a crack

Abstract

A modified geometric ray approach is used to predict the V(x,z) or the acoustic material signature of a circular point-focus scanning acoustic microscope for an isotropic surface containing a surface-breaking crack. The microscope response is assumed to consist of a specularly reflected geometric contribution, and the leaky contribution due in part to surface waves scattered from the crack. The long thin straight crack is presumed to be characterized by symmetric reflection and transmission coefficients. This approach is numerically simple and can be used to evaluate the response of acoustic lenses of various geometries. The method is used to predict line scan V(x,z0) response of a microscope in the vicinity of the crack for several defocus distances z0 and the results are compared with measurements.