Mass-Loaded Metamaterials Based on Polymer Matrix with Static-Dynamic Decoupling for Pressure-Resistant Broadband Underwater Sound Absorption.

Elastic metamaterials have been widely applied in elastic wave manipulation. Nevertheless, their performance is inherently restricted by two intrinsic coupling mechanisms: the modulus and density follow a power-law scaling relationship under static conditions, and the wave velocity is positively correlated with the modulus under dynamic conditions. To overcome these limitations, this study proposes a type of elastic metamaterial based on 3D-printed polymers, namely mass-loaded metamaterial (MLM). The structure is constructed by embedding discrete mass blocks into a lattice frame. The proposed design realizes the dual decoupling of modulus from density and wave velocity. The elastic modulus of the structure can be maximally increased by 307% while keeping the wave velocity constant; additionally, a 35% reduction in wave velocity can be achieved without deteriorating the elastic modulus. This distinctive decoupling effect possesses great application value in the field of underwater sound absorption. The structure can simultaneously exhibit high modulus and low wave velocity characteristics, which improves sound absorption performance and guarantees mechanical stability under high hydrostatic pressure.