Application and control mechanism of thin film metamaterials in underwater sound-absorbing materials at low frequency under high hydrostatic pressure

This study focused on developing a composite structure that utilizes thin film metamaterials to realize lowfrequency (0.1-1 kHz) underwater sound-absorbing. The sound-absorbing performance of the composite structure was assessed by investigating the effects of thin film materials, thickness, and mass block distribution using a combined approach of numerical simulation and experimentation. Results demonstrated that thin film metamaterials with lower modulus, such as silicon rubber (SR) thin film, have lower natural frequencies. In addition, a thicker SR film had a higher elastic strain energy density. Symmetrical mass block distribution was able to widen the absorbing bandwidth of the first three natural frequencies: improvements of 6 Hz, 2.8 Hz and 2.6 Hz were observed, respectively. Acoustic sample was fabricated and tested to verify the accuracy of numerical simulation. This study provided new insights into designing underwater sound-absorbing structures containing thin film metamaterials and supported the development of better stealth capabilities for underwater vehicles, especially in the context of low-frequency active sonar.