The acoustic material signature for a cracked surface using a point focus acoustic microscope

Abstract

Using an asymptotic model of a point focus scanning acoustic microscope, the acoustic material signature for a cracked surface is calculated. The scattered wave fields in the coupling fluid are related to the output voltage by an electromechanical reciprocity relation. This relation may be calculated using either asymptotically approximated wave fields or their asymptotically approximated spectra. Because this relation is linear, the component of the acoustic signature produced by the crack may be separated from that produced by a defect‐free surface. The component arising from the scattering from the crack is calculated from approximations to the wave fields rather than their spectra. It is assumed that the crack opening does not perturb the geometric wave field, but that it does strongly scatter the leaky Rayleigh wave, excited by the microscope. It is also assumed that scattering of the Rayleigh waves from the crack can be characterized by reflection and transmission coefficients. The wave fields scattered from the crack are thus calculated geometrically and the corresponding contribution to the acoustic signature is estimated. [Work supported by the MRC at UIUC.]