Scalable active acoustic metamaterials with programmable bulk modulus and mass density tensor

Passive acoustic metamaterials are constrained in their achievable properties and ability to integrate into realizable devices by unwanted property coupling, narrowband resonance, high loss, and challenges of fabrication. These limitations can be overcome by instead employing active components, such as speakers and microphones, to generate the desired acoustic response. We have developed an approach to designing scalable active metamaterials that allows for each unit cell to be of identical hardware and independent programming, but interact together as a bulk medium with desired effective properties. Unlike in a controls approach, the programming of these unit cells is a simple gain between local sensor and driver components. Here, we demonstrate an active metamaterial with individually programmable bulk modulus and mass density tensor. We validate its effective properties by comparing its experimental scattering behavior to that of simulated continuous media.