Analysis and experimental demonstration of an active acoustic metamaterial cell

Abstract

Active acoustic metamaterials (AAMM) have been developed to overcome the limited frequency bandwidth characteristics of passive acoustic metamaterials. The AAMM rely in their operation on using piezoelectric active ingredients in a fluid-solid composite structure forming the basic building block of a larger metamaterial periodic arrangement. A prototype of AAMM composite cell is manufactured and active control strategies are implemented on the piezoelectric elements to vary its stiffness in order to control the effective dynamic density of the cell. Acoustic characterization of the developed AAMM cell is carried out by measuring its acoustic impedance and transmission loss and comparing the results with the predictions of a finite element model. The obtained experimental measurements and the predictions of the finite element model are in very good agreement for the considered frequency range. The transfer functions between the reference microphone in the impedance tube and the piezoelectric elements demonstrate the coupling nature inside the cell rendering it to a system of single acoustic properties acting as a single degree of freedom system. The proposed AAMM can be useful in manufacturing the next generation of acoustic cloaks and metamaterials with controllable directivity and dispersion characteristics.