Low-frequency acoustic surface waves on a coupled membrane-cavity metasurface

We experimentally study the dispersion of localized acoustic surface waves (ASWs) supported by an array of coupled membrane-capped cavities. We design, simulate, and characterize a metasurface with a unit cell comprising a simple cylindrical air-filled cavity resonator topped with a tensioned membrane. We show that by tuning the resonance of constituent membrane or cavity, the behavior of the coupled system can reduce the frequency of the lowest supported surface mode by half compared to cavities without membranes. Experimentally obtained dispersion of the ASWs supported by the sample are compared with numerical predictions. With this mechanism, the operating frequency of acoustic surface modes can readily be altered by changing the physical parameters of constituent elements to tune the resonant frequency of the coupled cavity-membrane system.