Pressure-resistant metastructures based on sliced-TPMS lattices for waterborne sound insulation

Effective sound insulation in water often needs low impedance materials. The inherent conflict between low impedance and high stiffness presents considerable challenges in designing pressure-resistant sound insulation structures for underwater applications. Numerous studies have demonstrated that triply periodic minimal surface (TPMS) structures exhibit excellent mechanical properties, making them suitable for designing pressure-resistant structures. However, it remains unclear whether they can be utilized for underwater sound insulation. This work presents a novel design framework of pressure-resistant metastructures based on sliced-TPMS lattices for waterborne sound insulation. Eigenvalue analysis of the effective elastic matrix of typical TPMS structures shows that they do not possess easy deformation modes, which are crucial for achieving low impedance. A slicing design based on Gyroid lattices is introduced to release an easy deformation mode of the metastructure. Additionally, the balance between low impedance and pressure resistance is achieved through anisotropic design involving stretching the unit cell and rotating the material principal direction. A semi-analytical method that integrates the transition matrix method with asymptotic homogenization is developed to calculate the acoustic and mechanical properties of the metastructure efficiently. The results of mechanical and acoustic experiments demonstrates that the optimized anisotropic sliced-TPMS metastructure (with a thickness of 45 mm) can achieve exceptional sound insulation performance in the low-frequency broadband range (an average sound transmission loss of 9.2 dB across 200 Hz to 3000 Hz) under high hydrostatic pressure conditions (3MPa).