Tunable nonlocal purely active nonreciprocal acoustic media
Nathan Geib, Aritra Sasmal, Zhuzhu Wang, Yuxin Zhai, Bogdan-Ioan Popa, Karl Grosh
Abstract
Previously engineered wave-bearing materials including metamaterials generate their acoustic responses from a combination of passive geometrical structures possibly augmented by active elements. The passive geometrical features typically translate to uncontrolled properties outside the band of interest and are the source of adverse effects such as narrowing the operating band significantly or generating difficult-to-control instabilities due to interactions with the active elements. This paper proposes a nonlocal active metamaterial (NAM) architecture that employs a purely active approach to tailoring the acoustic field utilizing spatially separated sensors and actuators. A significant benefit of this approach is that the acoustic properties are described by analytical closed-form equations exposing the complex interplay between the various components of the material. The method is demonstrated by engineering extremely nonreciprocal wave transmission in an otherwise completely transparent subwavelength NAM. We experimentally demonstrate the remarkable flexibility of the system by electronically tuning the acoustic isolation characteristics and discuss the massive design space uncovered by the NAM approach.