Extraction of all coefficients of coupled-mode equations for natural, single-phase, unidirectional SAW transducers from dispersion characteristics computed by hybrid finite element method

A numerical method is presented for determining all of the coefficients of coupled-mode equations for natural, single-phase, unidirectional SAW transd ucer's (NSP-UDTs). Substituting numerical results computed by the hybrid fi nite element method for infinite NSPUDTs with shorted and open electric por ts into several relations derived from the coupled-mode theory, we can dete rmine all of the coefficients. Specifically, the edge frequencies of a stop -band and the static capacitances yield the self-coupling coefficients and the amplitudes of mutual-coupling and transduction coefficients, and the el ectric potential standing wave on the substrate surface, which can be deriv ed from the projection of the standing wave distributions of particle displ acements and electric potential in the whole substrate onto the set of thos e predicted by the coupled-mode theory, yields the phases of mutual-couplin g and transduction coefficients. NSPUDTs on ST-25 degreesX quartz, Y-51.25 degreesZ LiTaO3, and 50 degreesY-25 degreesX La3Ga5SiO14 substrates are inv estigated. Our results agree well with the earlier experimental ones.