Development Of A New Type Of Low-frequency And Wide-band Acoustic Metamaterials Earmuffs

In view of the shortcomings of the efficiency and large size of traditional sound-absorbing materials,the multi-order resonance sound absorption is studied to achieve high-frequency and low-band high-frequency absorption.Multi-order resonance means that a cell will have multiple absorption peaks,and then different cells will have different absorption peaks,so that the multi-cell and multi-order coupling together can greatly widen the sound absorption bandwidth.The multi-level resonance metasurface is constructed by inserting one or more partition plates with small holes inside the resonance cavity,so that it can obtain multiple multiples in a wider frequency band while maintaining the original sound absorption peak and the structure size.Almost perfect sound absorption peak.Compared with the structure of the traditional Helmholtz resonator,it is found that it not only has excellent high-order peaks,but also multi-peaks significantly increase the width of the sound absorption band.The paper mainly explores the following five aspects.First: In order to widen the sound absorption band of the local resonance structure,the mechanism of multi-order resonance sound absorption is analyzed and verified,and the theoretical calculation formula of multi-order sound absorption is deduced,considering the heat of the air in the Helmholtz resonance cavity Viscosity,the theoretical calculation of equivalent density and compressibility is introduced,and the effect of the change in aperture on the sound absorption characteristics of multi-order resonance is analyzed.Second: In order to achieve a good sound absorption effect,especially the low frequency broadband sound absorption effect,the size of the sound absorption structure is optimized.The genetic algorithm was used to optimize the design of the pore size,plate thickness,porosity,and depth of the back cavity.The optimal parameters were selected to complete the design of a single structure.Finally,the influence of parameters on the arrangement of the entire structure and the size of the entire unit is studied.Third: Due to the large sound absorption peak interval of a single multi-order resonance sound absorption supersurface,it is impossible to achieve continuous large-bandwidth sound absorption,so a multi-unit cooperative coupling design method is used to gradiently distribute the parameters of each unit to achieve low frequency Large broadband continuous soundabsorption.Fourth: The COMSOL Multiphysics software was used to perform finite element simulation calculations on the designed structure.With the continuous high sound absorption coefficient in the low frequency band as the design goal,the structure that meets the requirements of broadband sound absorption was designed by repeatedly improving the design and calculation.The back cavity of the structure is optimized,and the space-folding structure is used to replace the traditional straight back cavity,which reduces the overall thickness of the structure.Fifth: Using 3D printing technology,the designed sound absorption structure was prepared,and the sound absorption performance was tested by the standing wave tube test system to verify the actual sound absorption performance of the structure.The multi-order resonance structure studied in this paper not only has excellent sound absorption characteristics in the low frequency band,but also significantly widens the sound absorption band.Combined with the "acoustic siphon effect" design of the multi-unit coupling structure,the sound absorption band becomes wider and continuous.The acoustic superstructure has small size,frequency bandwidth and good sound absorption performance,and has good application prospects in engineering noise reduction.