Research project: Active control of viscoelastic 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. In this current research program a 1-dimensional active acoustic metamaterial is being investigated. The active materials is derived from a passive, Helmholtz resonator based design, where the applied control forces produce controllable double negative behaviour. A controller has been designed using both manual, heuristic techniques and using an H-infinity optimisation algorithm to attempt to maximise the region at which attenuation from the low frequency band gap occurs. The optimised controller architecture is being studied to gain insight into the structure a practical controller may take, allowing the active design process to be improved, and informing the design of high performance passive metamaterials.