Programmable bulk modulus in acoustic metamaterials composed of strongly interacting active cells

Active acoustic metamaterials are one path to acoustic properties difficult to realize with passive structures, especially for broadband applications. Here, we experimentally demonstrate a 2D metamaterial composed of coupled sensor-driver unit cells with effective bulk modulus (kappa(eff)) precisely tunable through adjustments of the amplitude and phase of the transfer function between pairs of sensors and drivers present in each cell. This work adopts the concepts of our previous theoretical study on polarized sources to realize acoustic metamaterials in which the active unit cells are strongly interacting with each other. To demonstrate the capability of our active metamaterial to produce on-demand negative, fractional, and large kappa(eff), we matched the scattered field from an incident pulse measured in a 2D waveguide with the sound scattered by equivalent continuous materials obtained in numerical simulations. Our approach benefits from being highly scalable, as the unit cells are independently controlled and any number of them can be arranged to form arbitrary geometries without added computational complexity.

Automated summary

In this experiment, an adaptive 2D acoustic metamaterials is demonstrated, in which the effective bulk modulus can be precisely tuned by adjusting the transfer function between sensors and drivers. The material shows high scalability and is capable of producing negative, fractional, and large effective bulk modulus as needed.