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 a S.A.W. resonator. With such tapering, Q-factors of 80,000 at 174 MHz amd 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.