The novel underwater acoustic metamaterial for improvement of sound absorbing in low and high frequencies

In this paper, a double-layer metamaterial composed of thermoplastic polyurethane (TPU) and nitrile butadiene rubber (NBR) which has a structure of metal oscillators (OS) is presented to improve the sound absorption behavior of underwater coating with a suitable bandwidth. The finite element method in COMSOL software was used to study and present the results and for verification, the presented results were validated with similar previous studies. Various materials with impedance matching for the underwater environment have been evaluated, and metal oscillators have been used to increase the absorption coefficient in medium frequencies, and finally, the influence of the type and geometry of the oscillators on the sound absorption coefficient has been investigated. The presented results show that by adding the nitrile butadiene rubber layer to thermoplastic polyurethane, the peak of the underwater absorption coefficient occurred in the range of 90% at a frequency of 600 Hz. In addition, by adding metal oscillators, the absorption coefficient range of 90–95% can be obtained in a frequency bandwidth of 600 to 10000 Hz and even higher frequencies.