Inverse design of structured materials for broadband sound absorption

This paper discusses the design of structured materials for broadband waterborne sound absorption. The structured materials are composed of a rubber matrix embedded periodically with cavities. To find the optimal distribution of cavities, an inverse design method based on topology optimization is proposed. Structured materials with novel hybrid cavities are thus designed. Efficient absorption over a wide frequency range between 600 Hz and 8000 Hz is achieved. The underlying mechanism behind the broadband absorption performance is revealed. Both the bending motion of the structured material and the translational motion of its steel backing affect the absorption in the low-frequency regime. Coherent coupling of local resonant modes together with the multiple scattering effects among cavities contribute to sound absorption in the mid-to-high frequency range. Moreover, a comparison with a conventionally structured material demonstrates the advantages of our design. Finally, an inverse design process with a different rubber matrix is performed. The results show that these cavities still exhibit similar topological features when the shear wave velocity of the rubber matrix is varied.