Controller architectures for optimum performance in practical active acoustic metamaterials

Over the last decade there has been significant interest in the design and production of acoustic metamaterials with physical qualities not seen in naturally occurring media. Progress in this area has been stimulated by the desire to create materials that exhibit novel behaviour when subject to acoustic waves,such as negative refraction or the appearance of band gaps in the frequency response of the material. Proposed designs range from locally resonant phononic crystals to arrays of Helmholtz resonators within ducts and past research has investigated both passive and active materials. Much of the research into active acoustic metamaterials remains theoretical, therefore to determine whether such materials are physically realisable and of potentially practical use it is important to understand the physical constraints that may arise in a produced active metamaterial. In this paper a 1-dimensional active acoustic metamaterial derived from a passive, Helmholtz resonator based design is considered where the applied control forces produce controllable double negative behaviour. The physical dimensions and active forces required to achieve the desired novel behaviour are explored for different architectures and any trade-offs that might have to be considered when producing a practically useful active metamaterial are identified