Demonstration of steering acoustic waves by generalized Eaton lens

Abstract

We demonstrate an acoustic generalized Eaton lens that steers an acoustic wave to a desired angle, to propose a design method for gradient-index devices using the sub-wavelength structure to shape an acoustic wave. Based on investigations on the effective parameter with several methods: the S-parameter retrieval method, Floquet-Bloch calculations, and multiple scattering theory (MST) for the cylindrical rigid rod structure, we speculate the design process to realize inhomogeneous refractive index distribution. For realization of a high effective index (∼2), the MST design inevitably fails, whereas the Floquet-Bloch calculations and S-parameter retrieval give identical results. By appropriately designing a two-dimensional array of cylindrical PMMA rods, we experimentally verify the acoustic generalized Eaton lenses for steering angles of 15° and 45°. Furthermore, the use of non-resonant metamaterials enables the proposed devices to work in the broad frequency range from 4 to 8 kHz.