Wavefront manipulation based on acoustic metasurface with membrane-helmholtz resonators

In this paper, a new type of gradient acoustic metasurface is designed to manipulate the transmissive wavefront freely. The developed acoustic metasurface is composed of a series of unit cells, which can provide the desired discrete phase-shift distribution and the high transmission efficiency in a wide range of frequency. Each unit cell consists of four membrane-Helmholtz hybrid resonators (MHHRs) and a straight pipe. The above design is based on the mixed resonance principle between decorated membrane, Helmholtz resonators (HRs) and the straight pipe. In this design, the refraction wave is oriented by phase gradient. To achieve the impedance matching between the metasurface and the background medium, the width of the pipe and the four cavities are optimized by genetic algorithm. Numerical simulations are carried out to demonstrate the potential applications in anomalous refraction, acoustic focusing, cylindrical wave to plane wave conversion, and negative refraction.