Phononic lens for suppressing diffraction of surface wave in lithium niobate substrate

Surface acoustic wave (SAW) devices are widely used as acoustic-electronic components today. The lithium niobate was often used as the substrate of SAW devices for its higher electromechanical coupling coefficient. In some applications like RFID tags and sensors, SAW devices have a long delay line and the energy loss of diffraction is considerable. Phononic crystals (PnC) have properties of band gaps and anisotropic propagation. In our previous study, self-collimation of SAW propagating in a tungsten/lithium niobate PnC was studied, and a PnC delay line was used to lower beam spreading. In this paper, we further analyze the anisotropic SAWs in PnCs systematically and then phononic lenses were designed to suppress diffraction in SAW devices. The thickness of PnC lens was optimized for high transmission of 210 MHz Rayleigh waves. The simulation showed that PnC lens can raise the performance of SAW devices with long delay lines.