Multicell Active Acoustic Metamaterial With Programmable Effective Densities

Abstract

Considerable interest has been devoted to the development of various classes of acoustic metamaterials. Acoustic metamaterials are those structurally engineered materials that are composed of periodic cells designed in such a fashion to yield specific material properties (density and bulk modulus) that would affect the wave propagation pattern within in a specific way. All the currently exerted efforts are focused on studying passive metamaterials with fixed material properties. In this paper, the emphasis is placed on the development of a new class of composite one-dimensional acoustic metamaterials with effective densities that are programmed to vary according to any prescribed patterns along the volume of the metamaterial. The theoretical analysis of this class of multilayered composite active acoustic metamaterials (CAAMM) is presented and the theoretical predictions are determined for an array of fluid cavities separated by piezoelectric boundaries. These smart self-sensing and actuating boundaries are used to modulate the overall stiffness of the metamaterial periodic cell and in turn its dynamic density through direct acoustic pressure feedback. The interaction between the neighboring layers of the composite metamaterial is modeled using a lumped-parameter approach. One-dimensional wave propagation as well as long wavelength assumptions are adapted in the current analysis. Numerical examples are presented to demonstrate the performance characteristics of the proposed CAAMM and its potential for generating prescribed spatial and spectral patterns of density variation. The CAAMM presents a viable approach to the development of effective acoustic cloaks that can be used for treating critical objects in order to render them acoustically invisible.