Investigation of phononic crystal reflective gratings for surface acoustic waves

Surface acoustic wave (SAW) devices are widely used as commercial products today. To improve their performance, hundreds of metal gratings are usually employed to reflect SAWs. In the last decade, phononic crystal (PC) attracted much attention for its special acoustic properties such as anisotropic propagation and band gaps. PC with tens of lattice periods can stop SAW within the band gap frequency ranges efficiently. Thus PC was proposed to be reflective gratings instead of metal strips to reduce the space-consuming of SAW devices. In this study, modified air/silicon PC structures with finite-depth cylindrical holes and tapered radius distribution were used to design high performance reflective gratings. SAW encountering various PCs was analyzed systematically to investigate the mechanism and optimize PC reflective gratings. With high efficient PC gratings, a resonant cavity for SAW was designed accordingly and the numerical analysis showed significant improvement. The maximum amplitude inside the cavity is five times larger than the peak inside the cavity defined by normal PC gratings.