Tunable active acoustic metamaterials

Abstract

We describe and demonstrate an architecture for active acoustic metamaterials whose effective material parameters can be tuned independently over a wide range of values, including negative material parameters. The approach is demonstrated experimentally through the design and measurement of two types of unit cells that generate metamaterials in which either the effective density or bulk modulus can be tuned. We show that these unit cells achieve negative refraction, negative effective mass density, significantly nonunity bulk modulus, and are suitable for the design of negative refraction media and media with tunable gain and absorption. In this architecture, a transducer senses the pressure wave incident on the metamaterial and an electronic circuit manipulates the electric signal produced and drives a second transducer that creates the acoustic response consistent with the desired effective material parameters. The electronics between the two transducers allows easy dynamic tuning of these parameters. We show that this approach can be applied to both broadband and narrow band designs.