Non-destructive Estimation of Surface Layer Structure from Surface Acoustic Wave Dispersion

The possibility of non-destructive estimation of a surface layer structure from the surface acoustic wave (SAW) dispersion was investigated. SAW on an aluminum block with a brass surface layer was generated by a pulse generator, and was observed by PZT sensors. The group velocity dispersion was estimated from detected waves by time-frequency analysis applied wavelet transform, and was in good agreement with theoretical group velocity. The inverse problem for estimation of material properties from the SAW group velocity dispersion was carried out. A new search strategy for an optimal solution considering the influence of each parameter on the dispersion curve was proposed. By this method, material properties could be estimated with error of only a few percent.