Highly efficient transmissive wavefront steering with acoustic metagrating composed of Helmholtz-resonators

Recently, a kind simply structured metasurface made of binary phase modulated meta-unit shows extraordinary beam steering functionality especially in the reflective beam manipulation. In this work, we demonstrate a Helmholtz-resonator based acoustic metagrating for high efficient beam wavefront steering in transmissive configuration. The complex meta-unit of the metagrating made of three Helmholtz-resonators combines traditional diffraction and interference theory with the free phase modulation ability of local resonant periodic structure to coherently control the acoustic wavefront steering. We show numerically and experimentally the anomalous refraction can be acquired with the designed metagrating of subwavelength thickness. By properly designing the geometric parameters of the meta-unit, the −1st order diffraction can be retained, and the unexpected diffraction orders are eliminated through destructive interference for a high efficient anomalous refraction. The anomalous refraction performance of the proposed metagrating is achieved over a wide incident range. The reported structure is promising for high efficient and wide angle complex wavefront engineering in e.g. encryption or communications