P3I-6 Interface Leaky Longitudinal Waves in Lithium Niobate and Lithium Tantalate

Interface acoustic waves with predominantly longitudinal elastic displacements in continuous materials of lithium niobate and lithium tantalate are reported. The interface is represented by the electrically conducting layer or periodic sequence of metal electrodes. The interface effective permittivity function shows a pronounced resonant behavior in YZ cuts of LN and LT at slowness values slightly higher the point, where longitudinal bulk wave propagates in continuous material. The periodic admittance characteristics are calculated for the metal electrode thickness to wavelength ratios in the range from 0.1 to 10%. The periodic admittance in YZ cut of LT shows a resonant behavior for quite small thickness to wavelength ratios in the range of 0.2 to 1% at the metallization ratio of 0.5. In YZ cut of LN the periodic admittance shows a resonance in the whole range of calculated electrode thicknesses. The propagation velocity determined by resonant frequency approximates the value of 7100 m/s. The relative bandwidth between resonance and anti resonance tends to be wider in the range from 0.33 to 1.43 % with increasing electrode thickness, while the resonant quality factor varies from 1600 to 220. The calculated temperature coefficient of frequency for all calculated values of metal thicknesses in YZ cut of LN does not exceed -33 ppm.