We report an underwater metastructure with excellent acoustic absorption that is constructed by perforating a helix structure into viscoelastic damping rubber. Finite element method results show that this metastructure can achieve the low frequency and broadband acoustic absorption below 1000 Hz. Waveform transformation, multiple scattering, and reflection energy dissipation mechanisms are the critical factors affecting the absorption performance. Different geometries and materials of the helix structure can adjust the acoustic absorption to a great extent. The proposed metastructure provides more possibilities for underwater acoustic manipulation applications.

We propose and discuss the elastic wave attenuation of hollow metamaterial beam embedded acoustic black hole. More abundant physical phenomena are given by modal analysis, shows that the band gap of three-dimensional acoustic black hole metamaterial is different from two-dimensional one. Lateral flexural vibrations occurs and make the original first two-dimensional band gap be compressed, and the opening of first three-dimensional band gap are caused by coupling effect between the longitudinal and lateral flexural vibrations. Below 1200Hz, only two band gaps exist, the geometric parameter m1 and angle γ could affect the band structure a lot, while the effect of geometric parameter m0 is a little less. Mutual validation of transmission spectra of vibration test and finite element analysis calculation and band gaps, illustrating its validity of the structure design, corresponding results could stimulate the realizations of three-dimensional acoustic black hole structure, particularly paves the way for the bridge from the corresponding theory of low frequency vibration and noise reduction to the practical application.