Low-frequency anechoic metasurface based on coiled channel of gradient cross-section

Abstract

This letter proposed advantageous in-uniform gradient cross-section (GCS) channels which weaken the dependence of the coiled-up anechoic metasurface on the total channel length. The privilege of GCS channels was revealed by studying Fabry-Pérot absorbers with designed channel widths. A theoretical framework was set up to explain the inherent sound absorbing mechanism, from which the overall performance as well as dominant working frequencies of linear and exponential GCS channels can be predicted. With proper GCS channel design, the proposed structures were experimentally and theoretically proven to achieve lower absorption frequencies in comparison with conventional uniform cross-section absorbers with the same exterior geometry. Through a parametric study on the near-perfect absorption frequency range of GCS absorbers, the strong tunability brought by GCS was confirmed, suggesting the possibility of on-demand frequency-oriented absorber design. Serving as an approach for acoustic impedance transferring, promising features of GCS can be extensively applied in existing coiled-up anechoic metasurfaces.