A hybrid acoustic cloaking based on binary splitting metasurfaces and near-zero-index metamaterials
Rui Yang, Xiaodong Zhang, Gang Wang
Abstract
A hybrid acoustic cloaking, composed of binary splitting metasurfaces (BSMs) and near-zero-index metamaterials (NZIMs), is proposed in this paper. The BSMs form acoustic cloaking to make the incident waves diffract around the obstacle, while NZIMs can straightly transfer the incident waves to the input layer of BSMs and control the emergent waves from the output layer of BSMs to propagate along the original incident direction. Due to the tunneling effect, NZIMs compensate for the extra phase from the wave diffraction and improve the efficiency of the acoustic cloaking. As BSMs and NZIMs consist of Helmholtz cavities and cylinders, respectively, the hybrid acoustic cloaking is simple in structure and easy to fabricate with only two-unit cell types per period. Additionally, an optimization method is applied to combine all layers of hybrid acoustic cloaking and realize a better cloaking effect. Using such a way, the normalized efficiency of transmitted waves through the hybrid acoustic cloaking can reach up to 97.2%, and scattered waves are strongly suppressed. For experimental demonstration, the actual sound field of emergent waves of acoustic cloaking is visualized with schlieren photography, where the cloaking effect is physically validated. This study simplifies the design of acoustic cloaking and provides further expansibility for wavefront transformations.