Acoustic metamaterials of modular nested Helmholtz resonators with multiple tunable absorption peaks

Abstract

The noise control for machines and equipment in the workshop is important to reduce the noise occupational diseases for the workers, and a novel acoustic metamaterial of modular nested Helmholtz resonators was proposed and investigated in this study. Based on the acoustic finite element simulation, the distributions of sound pressure, acoustic velocity and temperature variation at these resonance frequencies were obtained, which showed the sound absorption mechanism intuitively based on the Helmholtz resonance principle. The 14 structural parameters for the modular nested Helmholtz resonators with 5 nests were studied one by one, and the corresponding impact indexes to the resonance frequencies and peak sound absorption coefficients were summarized. By testing sound absorption coefficients of the prepared samples, the feasibility of the proposed acoustic metamaterial, the accuracy of the utilized finite element simulation method, and the usefulness of the selected optimization algorithm were validated. 4 sound absorption peaks were obtained in the target frequency points with thickness about 1/35th of the maximal working wavelength of sound wave. The number of sound absorption peaks was tunable through adding or reducing the number of the nested resonators. The proposed adjustable modular nested Helmholtz resonators is favorable to suppress the unfixed multiple narrowband noises.