Low-frequency underwater sound absorption metamaterial

Abstract Air bubbles in liquid are known for exhibiting low-frequency resonance and can be considered as passive scatterers. In this paper, we design an acoustic metamaterial consisting of an air bubble in a water-filled metal shell with an opening to develop low frequency underwater sound absorber. Numerical simulation is carried out by using finite element method, and the results show that the metamaterial sound absorber achieves quasi-prefect sound absorption coefficient (up to 0.96) at the frequency of 900 Hz based on the coupling resonance between the elastic bubble and the metal shell matrix. By replacing the single unit with a 3-unit composite structure, the acoustic metamaterial absorber can extend the working frequency from 830 Hz to1330 Hz, with still high absorption coefficient above 0.8. Our design acoustic metamaterial has potential applications in underwater noise control.