Hybrid Metamaterials Enable Multifunctional Manipulation Of Mechanical Waves On Solid-Fluid Interfaces

Mechanical waves exhibit complex propagations and waveform transitions on the interfaces of different media. By attaching an ultra-thin layer including local resonators on a solid panel, we demonstrate that this ultra-thin layer contains two control paths for solid and air, manipulating elastic and sound waves on the solid-air interface, respectively. Owing to simultaneously breaking the spatial symmetry of the solid panel and adjusting the boundary impedance of the solid-air interface, the proposed ultra-thin layer combines three operating states that are unique to each of the existing mechanical wave metamaterials. Specifically, we observe the "sound state" for intensely reflecting sound waves at the local anti-resonance, the "elastic state" for completely preventing elastic waves at the local resonance, and the "transition state" for totally converting elastic waves into sound waves at the entire monopole-type resonance. Hence, we denote such an ultra-thin layer as the "hybrid metamaterial." Our work may broaden the way of designing multifunctional materials and devices for manipulating mechanical waves.