Measurement of Microwave Acoustic Attenuation in Sapphire and Rutile using Nickel-Film Transducers

Initial investigations on the room-temperature acoustic attenuation in sapphire and rutile at S band, which were reported earlier, showed the attenuation in both of these materials to be relatively low. These measurements have now been extended to other frequencies, and curves of attenuation are shown for rutile shear waves and sapphire longitudinal waves covering the frequency range from L band to X band, and for sapphire shear waves from L band to S band. The attenuation has a nearly linear variation with frequency at the lower frequencies, and increases monotonically as frequency increases. This behavior may be attributable to Rayleigh scattering from submicron scattering centers within the crystals. Nickel-film magnetostrictive transducers, coupled to dielectric resonators, were used to generate the acoustic waves in the samples under study, and the acoustic attenuation was determined from echo measurements. Conversion efficiencies and certain other observed properties of nickel-film transducers over the above frequency ranges are also discussed.