A COMBINED FINITE-ELEMENT METHOD BOUNDARY ELEMENT METHOD TECHNIQUE FOR V(Z) CURVES OF ANISOTROPIC-LAYER SUBSTRATE CONFIGURATIONS

A numerical technique is presented to calculate V(z) curves for a line-for-us acoustic microscope, and for the specimen configuration of an anisotropic layer deposited on an isotropic elastic substrate. In this technique, the finite element method (FEM) and the boundary element method (BEM) are combined to calculate the scattered wave field on the specimen surface. The FEM is used in the layer and the BEM is used in the coupling fluid and the substrate. By combining the FEM with the BEM, the shortcomings of the two methods are avoided and their advantages are maintained. As a result, the present technique can be used for very thin and anisotropic layers. The V(z) curves are obtained by substituting the calculated wave field in an electromechanical reciprocity relation. The attenuation of the water used as the coupling fluid is taken into account by adjusting the calculated V(z) curves. The adjusted curves are compared with measured data, and very good agreement, both in the peak spacing and the amplitudes of the oscillatory curves, is observed.