Numerical time-domain simulation of wave propagation and scattering in acoustic microscopy for subsurface defect characterization

A numerical model of an acoustic microscope based on the elastodynamic finite integration technique (EFIT) is presented. It allows time-domain simulations of elastic wave propagation in both, fluids and solids, and includes focusing of the incident wave field as well as scattering at defects and the fluid-solid interface taking mode converted echoes and leaky Rayleigh waves into account. The simulations can be performed for different frequencies and materials and can be used for the continuous and time-resolved mode as well as for transmission and reflection microscopy. The simulation results can be represented by time-domain signals and wave front snapshots. The formation of V(r,z) curves is also possible. In the present paper the simulations are applied to the problem of vertical cracks and spherical inclusions in a solid substrate as well as for subsurface characterization of thin coatings.