Sandwich plate-type metastructures with periodic graded resonators for low-frequency and broadband vibration attenuation

A floating-raft vibration-isolation system can effectively inhibit the transmission of mechanical vibration energy to the hull. In this study, a new sandwich plate-type metastructure (SPM) raft is designed based on the construction of acoustic metamaterials for vibration isolation. Unlike conventional rafts, the SPM features periodic rubber-mass subsystems arranged in the core layer of the sandwich plate, as well as faceplates slotted to reduce the mass and offset the weight increase caused by additional resonators. An equivalent model of an SPM with graded resonators is established, and the dispersion equation is derived by combining Kirchhoff's law and Bloch's theorem. Based on dispersion analysis, multiple bandgaps lower than 200 Hz, through which elastic waves cannot propagate, are identified. The vibration transmission performance of the SPM is analysed via finite-element simulation. The numerical results show that the proposed SPM exhibits low-frequency vibration attenuation and that the frequency band in which vibration attenuates is robust. Finally, vibration-transmission experiments are conducted, and the effectiveness of the proposed SPM is validated. This design strategy provides new possibilities for the development of sandwich structures for ship vibration and noise control.