Wave Propagation Control Using Active Acoustic Metamaterials

Abstract

Acoustic metamaterials (AMM) are artificial materials with engineered sub-wavelength structures that possess acoustic material properties which are not readily available in nature. The material properties of AMMs can be manipulated by embedding active elements inside their structure (active AMMs). This manipulation of properties is done by an external voltage signal and is hardly available in any natural material. In this work, existing designs for passive and active AMMs are reviewed and summarized. Existing homogenization techniques for the material properties of passive metamaterials are investigated and extended to be applied for active AMMs. Three new designs for active plate-type AMM with tunable density are proposed and verified analytically, numerically and experimentally. The first design is a one dimensional (1D) AMM consisting of clamped piezoelectric disks in air. The effective density of the material is controlled by an external static electric voltage. An analytic model based on the acoustic two-port theory, the theory of piezoelectricity and the pre-stressed thin plate theory is developed to predict the behavior of the material. The results are verified using the finite element method. Excellent agreement is found between both models for the studied frequency and voltage ranges. The results show that the density is tunable within orders of magnitude relative to the uncontrolled case. This is done with a limited effect on the bulk modulus of the material. The results also suggest that simple controllers could be used to program the material density.