Stoneley wave excitation by a bounded beam at the down-step of a thin layer on a substrate

The mode conversion of a bulk wave into a Stoneley wave at the downward step of a thin layer partially covering a solid substrate is studied. An analytical expression for the amplitude of the excited Stoneley wave is derived by applying mode theory. The excitation amplitude has two pronounced maxima: at grazing and at Rayleigh angle incidence of the bulk wave. The latter maximum is almost independent of the material characteristics of the thin layer.