An underwater absorber consisting of a microperforated panel, foldable channel and rubber coating with perfect low-frequency sound absorption, broadband absorption and strong resistance to deformation is presented. The theoretical prediction and simulation analysis are in good agreement. It is demonstrated that sound energy is mainly dissipated in the rubber coating due to waveform conversion at the coupling boundary. A meta-structure with low-frequency and broadband absorption is realized by optimizing the structural parameters. Moreover, at a relatively regulated low-frequency wavelength, the spatial folded structure enables a deep subwavelength dimension. The proposed meta-structure has wide potential applications in underwater noise control.

We propose a coupled square-neck embedded Helmholtz resonator (S-NEHR) with a deep-subwavelength thickness. By precisely designing each cell peak, the average sound-absorption coefficient of the nine coupled S-NEHR structures is greater than 0.9 at 300-410 Hz, and the thickness is only 1/30 of the working wavelength. Adding a microperforated panel (MPP) in front of the coupled structure enables a smaller size and larger bandwidth (500-1000 Hz). The simulation and experimental results demonstrate that the S-NEHR structure has great application prospects in engineering noise control due to its extraordinary sound-absorption properties and compact structure.