Continuously Tunable Acoustic Metasurface for Transmitted Wavefront Modulation

Abstract

Previously reported acoustic metasurfaces that consist of fixed channels, are\nuntunable to meet the broadband requirement and alterable functionalities. To\novercome this limitation, we propose screw-and-nut mechanism of tunability and\ndesign a type of continuously tunable acoustic metasurface with unit components\nof helical cylinders which are screwed into a plate. The spiral channel length\ncan be tuned continuously by the screwed depth; and then a metasurface with\ncontinuously tunable acoustic phase at independent pixels is attained.\nDifferent distributions of the unit components can shape an arbitrary\nmetasurface profile. We also developed an approximate equivalent medium model\nto predict the tunability of the unit component. As an example, we present the\ndesign details of a circular tunable metasurface for three-dimensional acoustic\nfocusing of different airborne sound sources in a wide frequency region. A\nsample of the metasurface is manufactured by poly lactic acid (PLA) plastic\nwith the helical cylinders being 3D-printed. Experiments of sound focusing are\nperformed. It is shown that the results of the equivalent medium model, the\nfinite element simulation and the experiments are in a good agreement.\n