Investigations on working principles and design methods for metamaterial silencers

Acoustic metamaterials (AMM) are a promising approach for the development of innovative, compact, fiber-free silencers with customized acoustic properties. The integration of active transducer systems in AMM provides further potential for significantly increasing the acoustic efficiency. For the development of commercially viable AMM silencer systems, practical design methods and economic manufacturing processes are required, which are currently not available. In the Fraunhofer research project »MetaVib« passive and active AMM silencer concepts for duct and splitter silencers are investigated. The AMM silencers are designed, prototypically manufactured and experimentally validated. Besides the acoustic efficiency, the design also considers the manufacturability on an industrial scale. This conference paper discusses the working principle of Bragg reflections and the modelling of a periodic waveguide using the transfer matrix method in combination with the Bloch-wave theory and the FEM. The simulations and experimental results for an arrangement of simple lambda/4-resonators are in good agreement. In addition, the paper presents first compact resonator concepts. To date these concept resonators are manufactured using 3D printing. However, they are designed to be mass producible using standard injection moulding processes. Concepts for the integration of active components into the concept resonators are also presented and discussed.