Least action principle for the estimation of the slowness and the attenuation of pseudo surface acoustic waves.

The estimation of the slowness and of the attenuation of pseudo surface acoustic waves (PSAWs) has been addressed by many authors, but still represents a challenge because of the intrinsic difficulty to provide a physically consistent representation of their characteristics. In this work, we propose an alternative approach to the popular use of complex slownesses along the propagation direction. We introduce in the standard harmonic model an optimal source term exactly compensating for the energy lost by leakage, by analogy with the problem of the reflection of a bulk acoustic wave on the surface. This leads us to the minimization of a function whose minimum is the PSAW slowness and whose minimum value gives the attenuation. The method is found to be stable and reliable compared to previously published data, without requiring any change in the partial wave selection rule, and further does not require one to consider waves with increasing energy in the depth of the substrate, which generally does not correspond to the observed phenomena. [ABSTRACT FROM AUTHOR]