A low frequency underwater meta structure composed by helix metal and viscoelastic damping rubber

Abstract

Many underwater acoustic absorption materials have been proposed, but good low frequency acoustic absorption remains a challenge. We report an underwater metastructure with excellent acoustic absorption that is constructed by perforating helixes of metal into viscoelastic damping rubber. Finite element analysis shows that this metastructure can achieve an acoustic absorption coefficient of 0.75 at about 100 Hz with a thickness of only 1/68 wavelength at the same frequency. Compared with a homogeneous viscoelastic rubber material, the addition of the helix structure improves the acoustic absorption ability in the range of 0–1,000 Hz. An analysis of vibration displacement maps indicates that waveform transformation, multiple scattering, and reflection energy dissipation mechanisms are the critical factors affecting the absorption performance. Different geometries and materials can adjust the sound absorption characteristics below 1,000 Hz. The proposed metastructure has the advantages of high acoustic absorption ability, broader frequency bandwidth, and regular geometry, providing more possibilities for underwater acoustic manipulation applications.