Nonlinear interaction between oppositely propagating surface waves

The nonlinear interaction between two oppositely directed surface acoustic waves (SAW) is analyzed. It is shown that the surface boundary conditions lead to the generation of up to three bulk waves at the sum frequency of the two input waves. The interaction is characterized by two frequency-independent parameters which are related to the total surface displacement at the sum frequency and the strength of the bulk waves generated. These parameters are calculated for a number of materials of technological interest.