Rayleigh wave reflection from single surface imperfections on isotropic substrates

The specific features of the Rayleigh wave reflection from single surface imperfections of an isotropic substrate are studied by the finite element method. Six types of the imperfections are considered, namely, upstep and downstep, projection and groove, and strip of foreign material coating the substrate and buried into it. The dependence is found and analyzed of the absolute value and the phase of the reflection coefficients on the geometrical parameters of defects and the angle of incidence. Numerical results are compared to analytical predictions based on a development of the reflection coefficient in powers of the defect height to wavelength ratio $h/λ$ and limited to the first-order term. In particular, this comparison reveals that in some cases approximate expressions are able to provide a good precision. At the same time situations are met when the linear approximation fails to describe the behavior of the reflection coefficient even at fairly small $h/λ$⁠.