Nanoporous Metamaterial Composites for Enhanced Underwater Low-Frequency Acoustic Attenuation

Abstract

This study introduces a nanoporous TiNi-polymer metamaterial designed to overcome the long standing limitations of conventional underwater absorbers in the low frequency regime. By incorporating TiNi shape memory alloys as an active functional phase within a viscoelastic polymer matrix, the composite exploits transformation induced damping, tunable stiffness, and multi scale interfacial dissipation to significantly enhance acoustic energy attenuation. A fully coupled acoustic-thermal-mechanical model is developed to capture the interactions among wave propagation, structural deformation, and internal friction within the hybrid architecture. Complementary experimental testing of TiNi reinforced polymer specimens validates the practical feasibility of the impedance gradient concept. The results demonstrate that the synergy between nanoporous transport pathways and TiNi driven damping enables broadband low frequency absorption and reduced reflection, establishing a lightweight and adaptable underwater acoustic metamaterial platform. Overall, this work provides a design framework in which shape memory alloy functionality serves not merely as structural reinforcement but as a central mechanism for achieving enhanced underwater acoustic performance.