Effect of anisotropy on characteristics and behavior of shear horizontal SAWs in resonators using langasite

Orientations of langasite (LGS) with Euler angles (0°, μ, 90°) are potentially useful for applications in wireless SAW sensors because of wide variation of their temperature coefficient of frequency (TCF), between -50 and +50 ppm/°C, combined with high values of electromechanical coupling coefficient, especially if thick electrodes are utilized. The nature and characteristics of shear-horizontally polarized SAWs (SHSAWs) propagating in these orientations are investigated using a combination of numerical techniques: analysis of the BAW slowness surface and its effect on the SH-SAW structure; visualization of displacements that follow wave propagation in the grating; calculation of admittance of infinite periodic gratings; and analysis of SAW dispersion in the gratings, including possible interaction between SH-SAWs and parasitic Rayleigh SAWs. The characteristics of SH-SAWs propagating in symmetric cuts (velocities, localization depth, electromechanical coupling, etc.) are supplemented by analysis of propagation directions deviating from the YZ-plane toward the x-axis of LGS, for the temperature compensated cut with Euler angles (0°, 22°, 90°) and one more orientation for comparison. This extended analysis reveals that in actual devices, the anisotropy may be a reason for strong interaction between SH-SAWs and parasitic Rayleigh SAWs and cause degradation of the device's performance.