Reciprocity is one of the fundamental properties in the field of wave propagation. In acoustics, this property helps in various practical applications. But, breaking this reciprocity also has useful applications. As a result of which, many researchers have tried to break the reciprocity in acoustics, which is comparatively difficult, unlike in fields such as electro-magnetics.

Majority of these proposed methods to break the reciprocity are hard-wired systems, which work for a very limited frequency range. Thus, we have introduced a non-reciprocal metamaterial having boundary control with the help of piezoelectric sensors and actuators. A theoretical model is introduced to induce the nonreciprocal behavior, and it is backed up by providing experimental evidence.

Our setup consists of a cylindrical cell made up of acrylic, filled with water, having four piezo sensors/actuators, two on each end. The idea is to excite the piezo cell through an actuator on one side, collect the resulting signal from the piezo sensor on the other side, and perform appropriate mathematical operations on this signal to produce a feedback/control signal via a specially designed dynamic control action.

This control signal affects the propagation of pressure waves through the water medium inside the cell as it introduces a virtual gyroscopic effect of controlled magnitude and direction. Thus, this is how non-reciprocity is introduced and controlled into the metamaterial cell. The obtained theoretical and experimental results demonstrate the effectiveness of the dynamic controller in breaking the acoustic reciprocity. Extension of this work to multi-cell metamaterial configuration is natural extension to be pursued.