Tunable Broadband Reflective Acoustic Metasurface

In advancing the performance of metamaterials, key features nowadays are tunability and a wide range of operating frequencies. Here a helical acoustic metasurface, capable of providing a modulated wavefront of reflected sound with continuously tunable broadband operation, is demonstrated. The authors' matched screw-and-nut mechanism can lead to pragmatic applications of metasurfaces for three-dimensional control of sound. This concept for continuous tuning is an important step for achieving broadband, multifunctional acoustic metasurfaces, and may inspire designs featuring curved tunable, active programmable, or randomly coding metasurfaces.