A metasurface composed of orifice-type unit cells for the redirection of acoustic waves

Abstract

To implement a sound wave redirection system, a two-dimensional (2D) slice of a three-dimensional (3D) metasurface is designed and fabricated using a one-dimensional (1D) face-centred orifice cubic (FCOC) unit cell. The metasurface consists of five identical periodic groups, of which one periodic group consists of eight unit-cell groups with a phase shift of pi /4 adjacent to each other. One unit-cell group consists of four 1D FCOC unit cells with the same orifice diameter. From the numerical simulation results of the designed metasurface, we observed the redirections of sound waves and compared them with the expected theoretical results. It was confirmed that the experimental results agree well with the simulated results with respect to the different incident angles and frequencies. The used frequencies that satisfy the homogeneous medium condition of the metamaterial for the redirection of incident waves range between 1500 and 2700 Hz. At the characteristic frequency of 1540 Hz at normal incidence, it is considered that stationary evanescent waves exist at the boundary of the metasurface due to the characteristics of the surface wave and the limited end boundary. The FCOC-based metasurface provides a new method of metasurface fabrication and is expected to expand the applicability of the metasurface because it can be easily applied to a surface with any shape.