Energy harvesting of Rayleigh surface waves by a phononic crystal Luneburg lens

Abstract

In this paper, a phononic crystal (PnC) Luneburg lens is designed for harvesting the mechanical energy of Rayleigh surface waves. The square-latticed PnC is formed by drilling holes periodically in an aluminum matrix. The PnC Luneburg lens for Rayleigh surface waves is constructed by spatially modulating the hole radius of each PnC unit-cell according to the refractive index profile of a conventional Luneburg lens. To convert mechanical energy into electricity, a piezoelectric disk is attached at the focal point of the PnC Luneburg lens, where the Rayleigh surface waves are focused. Compared with the reference harvester on a homogeneous aluminum matrix, the electric power outputs are significantly enhanced by the PnC Luneburg lens harvester for two typical directions, namely the ΓX and ΓM directions. For either the ΓX or ΓM direction, the amplification ratio of the PnC Luneburg lens harvester is over 14.