Tunability of stop bands in thermoformed vibro-acoustic metamaterials solutions for increased noise insulation

Recently, resonant metamaterials have caught attention due to their lightweight design and superior noise insulation performance at defined and tunable frequency ranges, called stop bands. Nevertheless, the production processes of such noise insulation solutions are still expensive and therefor hindering application in industry. This paper explores the use of thermoforming, which is a cheap and common industrial production process, to manufacture a metamaterial panel. In this way, resonant metamaterials are brought closer to a realizable industrial noise insulation solution. In previous work, the authors have shown the use of such a thermoformed metamaterial panel in a resonance driven acoustic environment. In this paper, the main focus is on the tunability and robustness of the concept. The structural vibration behaviour and the noise insulation performance of the produced metamaterial panels are experimentally assessed by hammer testing and insertion loss measurements respectively. A strategy to widen the zone of influence, by combination of stop bands, is also experimentally investigated by combining two different tuned locally resonant parts in one panel. Furthermore, a panel with less resonant parts is manufactured to verify the robustness of the proposed solution. In conclusion, the created metamaterial thermoformed panel is lighter and provides superior experimentally evaluated noise and vibration insulation performance for all the studied cases in the frequency regions of their tuned stop bands.