Active nonreciprocal acoustic metamaterials using a switching controller.

Abstract

A class of active acoustic diodes and metamaterials is developed to control the flow and distribution of acoustic energy in acoustic cavities and systems. Such development departs radically from the currently available approaches where the non-reciprocities are generated by hard-wired designs, favoring one transmission direction which is dictated by the arrangement of the hardware and hence it cannot be reversed, or without the presentation of rigorous control theory analysis. The proposed active nonreciprocal acoustic metamaterial (ANAM) cell consists of a one-dimensional acoustic cavity provided with active flexible boundaries. These boundaries are made from piezoelectric bimorphs interacting with the cavity to monitor the pressures of the propagating acoustic waves. The outer layers of the bimorphs provide the necessary control actions by direct application of the appropriate control voltage on each layer or by proper connection of nonlinearly activated shunted networks of switching resistors. The control of the switching is carried out using a Switching Mode Control (SMC) strategy. In this strategy, a lumped-parameter model of the ANAM cell is developed to predict the nonreciprocal characteristics of the cell by proper selection of the slope of the switching surfaces. Numerical examples are presented to demonstrate the merits of the proposed SMC.