Design of Load-Bearing Materials for Isolation of Low-Frequency Waterborne Sound

Materials with extremely low impedance like air can insulate efficiently waterborne sound, particularly at low frequency, however the poor resistance to load hinders further their applications. This work demonstrates that the elastic anisotropy of materials can not only achieve extremely low impedance, but also high enough stiffness for load bearing. A dimensionless quality factor is proposed to characterize integrately the performance on sound insulation and load bearing of anisotropic materials. It is found that this factor has an upper bound of unity and the corresponding conditions are derived for some particular anisotropic materials. By setting the quality factor to be unity as an objective function for microstructure optimization, a methodology based on topological optimization is proposed to design the microstructure of the corresponding materials with optimized integrated performance on waterborne sound insulation and load bearing. The obtained optimized material is validated by numerical simulation and by comparing with other similar waterborne sound insulation materials with low impedance. This study paves the way for designing load-bearing materials with extremely low impedance, and opens a route to control low-frequency underwater waves.