BROADBAND AND QUASI-PERFECT ACOUSTIC ABSORPTION WITH BIO-INSPIRED HIERARCHICAL METAMATERIALS FOR AIR AND SURFACE TRANSPORTATION SYSTEMS

Aircraft noise has become a major concern for communities around airports giving rise to stacked legislations and regulations at various levels. Current noise reduction technologies do not seem to achieve the targeted reductions set by the EC experts by the ACARE Flightpath 2050. Classical control methods can provide significant noise reduction but may add additional mass causing excess drag and degradation of the aircraft aerodynamic performance. The general goal of this proposal is to create meta-structures able to efficiently dissipate flow-induced noise without requiring increasing area or added weight. We have proposed a novel type of high performance acoustic treatment made up of Micro-Capillary Plate (MCP) absorbers. MCPs consist of highly porous panels made up of leaded glass, of high porosity (greater than 60%) since their surface contains millions of micro-channels per centimeter square, the holes or square channel dimensions varying between 5µm and 50µm. These characteristics provide them with exceptional acoustical properties compared to other classical absorbers or MPPs. For instance, if rigidly backed by an air cavity of 24 mm, a MCP device provides a half-bandwidth absorption over 12 octaves whereas a MPP device works only over two-three octaves. The project outcomes allow practical selection of the meta-material architecture that best suits specific applications. For instance, they can be used for duct geometries in air-conditioning and ventilations systems.