Surface acoustic wave depth profiling of elastically inhomogeneous materials

The potential of Rayleigh wave spectroscopy for the in-depth reconstruction of elastic properties of multilayers for materials with a continuous profi le of elastic properties is explored. Two models to calculate the surface a coustic wave (SAW) dispersion spectrum from the profile of the elastic para meters are elaborated and compared. It is found that the relevant elastic p arameters for Rayleigh wave dispersion in multilayers are the "effective" R ayleigh velocities, i.e., the Rayleigh velocities calculated for virtually semi-infinite layers. For the solution of the inverse problem, a neural net work and a singular value decomposition model are proposed and tested on si mulated SAW spectra. The reconstruction techniques are applied to reconstru ct the elastic depth profile of shot-peened steel samples from laser-genera ted and laser-detected SAW data. (C) 2000 American Institute of Physics. [S 0021-8979(00)00920-8].