Features of the reflection of an acoustic beam from a surface with nonuniform boundary conditions. I. Theoretical analysis

Features of the reflection of an acoustic beam from a surface with nonuniform boundary conditions of the free-rigid, free-slip, and slip-rigid types are theoretically analyzed. It is shown that it is fundamentally possible to substantially increase the sensitivity and reliability of evaluations of the quality of the cohesion between materials. This can be done via selection of the spatial position of a PET, as well as selection of the incidence angles of an acoustic beam at which the phase shift φD between waves reflected from surface areas with different boundary conditions is nonzero and, if possible, close to ±π. In this case, interference results in a substantial change in the amplitude of reflected waves depending on their reception angle. The features of changes in the field of reflected elastic waves upon intersection of the boundary of a defective region with an acoustic-beam spot are analyzed (in the 2D-formulation) for discrete and linear changes in φD.