Active Acoustic Resonators and their Applications to Loss-Immune, Reconfigurable, or Dynamic Metamaterials

Locally-resonant sonic metamaterials refer to synthetic acoustic matter composed of artificial acoustic “atoms”, generally passive, and of subwavelength sizes, that are capable of resonantly interacting with an external acoustic wave, and manipulate it in ways that are not directly available using natural bulk materials. Such artificial 3D materials, or their 2D analogs called metasurfaces, have led to extraordinary physical phenomena including negative refraction, subwavelength focusing, guiding or absorption, cloaking, or anomalous reflection/transmission. Despite these interesting phenomena, the use of passive resonators as building blocks for metamaterials comes with drastic limitations, in particular in terms of bandwidth, sensitivity to absorption losses, reconfigurability, etc. In this presentation, we will demonstrate theoretically and experimentally that active electro-acoustic resonators, when properly designed, can form the basis for efficient metamaterial building blocks. We will demonstrate subwavelength resonators whose fundamental properties like absorption losses, resonance frequency, and radiative losses, can be controlled independently using an active feedback control scheme. We will demonstrate their use in various examples of active metamaterials that exploit this active scheme for either immunity to absorption losses, disorder, non-reciprocity or for reconfigurability.