Sound pollution is an omni-present problem in our society affecting population health and well-being and the quality of life. Technical solutions to reduce the impact of sound in a broad frequency range are therefore of vital importance. Such solutions however be economically attractive, since the volumes of sound insulation required in our society are extremely large.
Acoustic foams are nowadays one of the best solutions towards this problem. However, they are mainly effective in the mid- and high-frequency regime. This drives the need for innovations targeting a broad frequency regime and low frequencies in particular. This ERC-PoC project focused on acoustic metafoams, as a special class of dynamical metamaterials proposed in a prior ERC-AdG project. This novel class of materials are enriched acoustic foams, whereby a mass is implemented in the cavities of the foams. The resonance of all these masses triggers the meta-behaviour of the resulting metafoam and is expected to be particularly efficient at lower frequencies. This proof-of-concept project aimed to assess this basic idea and bring it to practice. In order to reach this objective, attention has been given to different metafoam manufacturing methods, also a route having potential for large volume production (and low cost) and the validation of the actual performance of the metafoam.
Metafoams have been produced following 3 different processing routes. The first lab-based routed consisted in the direct insertion (by injection, spin coating or mixing) of particle-emulsions (glass or steel) in acoustic foams, which are subsequently dried to yield the particle-enriched metafoam. The second route, based on Polymerized High Internal Phase Emulsion, has been assessed as well, but it was less effective in producing metafoams suitable for low frequencies. The third processing route has been executed in collaboration with an industrial partner, in order to provide a scalable manufacturing method. Metafoam samples have been produced with compression moulding on the one hand, and at the very end of the project also with an extrusion process. The different series of metafoam samples were tested in a transmission tube setup, which indicated that certain series and sample configurations indeed yield promising results in terms of a decreased sound transmission.
Based on the promising nature of the results obtained, a market and intellectual property analysis has been performed, exploring market opportunities for metafoams.
