Designing Hyper-Thin Acoustic Metasurfaces with Membrane Resonators

Abstract

We design extremely-thin acoustic metasurfaces, providing a versatile platform for the manipulation of reflected pressure fields, that are constructed from mass loads and stretched membranes fixed to a periodic rigid framework. These metasurfaces demonstrate deeply subwavelength control and can have thicknesses an order of magnitude less than those based around Helmholtz resonators. Each sub-unit of the metasurface is resonant at a frequency tuned geometrically, this tunability provides phase control and using a set of finely tuned membrane resonators we create a phasegrating metasurface. This surface is designed to exhibit all-angle negative reflections with the ratio of wavelength, λ, to thickness, h, of λ/h ≈ 23.1, and to create a flat mirror using the phase profile of an elliptic reflecting mirror. A further important acoustic application is to sound diffusers and we proceed to design a deeply subwavelength membrane-based meta-diffuser that can be two orders of magnitude thinner than the operating wavelength, i.e. thickness ≈ λ/102. This paves the way for developing advanced acoustic metasurfaces with applicability to functional acoustic devices in sound-related industries.