MODE THEORY AS A FRAMEWORK FOR THE INVESTIGATION OF THE GENERATION OF A STONELEY WAVE AT A LIQUID-SOLID INTERFACE

A theoretical model, based on mode theory for acoustic waves, is presented in order to describe the complicated scattering of an ultrasonic volume or surface wave at the boundary between two adjacent liquids abutting a single solid. Analytical expressions for the displacement fields of the scattered and mode-converted waves are derived. In particular, it is shown that a volume wave incident from the liquid of the first liquid/solid structure can generate a Stoneley wave along the interface of the second liquid/solid structure. The relative amplitude of the displacement of the excited Stoneley wave is calculated for several (liquid-liquid)/solid configurations. The angle of most efficient excitation can be derived from the maximum of the function describing the interaction between a radiation mode and a Stoneley eigenmode in the division plane separating both liquid/solid structures.