Impact of coupling between multiple SAW modes on piston mode operation of SAW resonators

The piston mode operation (PMO) is quite effective for realization of spurious-free and low-loss SAW resonators. The scalar potential (SP) analysis indicates that “phase shifters” are necessary for PMO at edges of the acoustic aperture. Nakamura, et al., pointed out that for SAW resonators using SiO
₂
/LiNbO
₃
structure, PMO is possible by simply removing SiO
₂
in the dummy electrode region [1]. This phenomenon cannot be explained by the SP theory, and was expected to be due to existence of the spurious SH SAW in addition to the main Rayleigh SAW or vice versa.