Response of line focus acoustic microscope to specimen containing a subsurface crack

A numerical model is presented to calculate V(z) and V(x, z) curves for a line focus acoustic microscope and a specimen containing a subsurface crack. In this model, a Gaussian beam which is tracked through the lens into the coupling fluid and into the specimen, interacts with the crack. The numerical approach is based on the solution of singular integral equations by the boundary element method. The system of singular integral equations follows from the conditions at the interface of the coupling fluid and the specimen and on the faces of the crack. An electromechanical reciprocity relation is used to express the voltage at the terminals of the microscope's transducer in terms of the calculated incident and back-scattered fields. V(z) and V(x, z) curves are presented for various locations and orientations of the crack. The characteristic features of the V(z) and particularly the V(x, z) curves, as they relate to crack configuration, are discussed in some detail.