Suppression of bulk-scattering loss at s.a.w.-resonator reflectors

Tapering of the groove depth at the edges of grooved-array reflectors is shown to be effective in suppressing surface-to-bulk-wave conversion losses at such reflectors in an s.a.w. resonator. With such tapering, Q-factors of 80,000 at 174 MHz and 61,000 at 157 MHz have been measured on evacuated LiNbO3 and s.t.-quartz resonators, respectively. These measurements were made on `empty¿ resonators having no transducers between the gratings. The latter value is within 3% of the best estimate of the material Q-factor of 63,000 at 157 MHz.