Research On Low-frequency Sound Insulation Performance Of The Second-order Acoustic Metamaterial Panel

Due to the long wavelength of low-frequency noise,it is difficult to be blocked by obstacles.Therefore,low-frequency sound insulation has always been the focus and difficulty of noise control research.In recent decades,the development of acoustic metamaterials has opened up a new research direction for low-frequency sound insulation.Large area low frequency sound insulation is one of the development trends and research hot spots of plate-type acoustic metamaterials(PAMs)used in engineering practice.The PAM extended structure can be constructed by unit cell array.However,the sound insulation performance of the PAM extended structure cannot simply capture the sound insulation performance of the unit cell,but is closely related to the number of unit cell.In view of the above problem,this paper focuses on the research on the low-frequency sound insulation performance of the local resonant PAM as follows:1)In this paper,based on the Rayleigh method,the analytical calculation of fundamental frequency of the PAM unit cell is conducted,and the results are compared with the finite element simulation results.The results show that there is a large error in the analytical solution of the fundamental frequency when the central mass block is simplified to a concentrated mass.On this basis,a practical mass model considering the actual shape and size of the mass block is proposed.By comparison,the error of the analytical solution of the fundamental frequency based on the actual mass model is obviously reduced.2)The sound insulation mechanism of single unit cell and composite cell was explained from the perspective of modal coupling antiresonance,and the sound insulation performance of PAM extended structure with different number of cells is simulated by using acoustic-structure coupling module.It is found that with the increase of the number of cells,the resonant modes of the entire panel are gradually introduced from the high frequency to the low-frequency range,which damages the original anti-resonance mechanism of the cell mode coupling,and makes the low-frequency sound insulation performance of the PAM extended structure become worse.the effects of mixing of different unit cells on the sound insulation performance of the PAM extended structure are simulated.It is found that different mixing methods have little effect on the sound insulation performance of the structure,while different mixing ratios have a certain effect on the sound insulation performance of the structure.3)In order to solve the problem of poor low-frequency sound insulation performance of PAM extended structure,a new design idea of high-order PAM is proposed in this paper,which is characterized by adding an extra high-order mass block to the center of PAM extended structure,and the sound insulation performance of second-order PAM is studied.Because the second-order mass block enhances the coupling antiresonance between the resonant modes of the entire panel and the unit cell,the low-frequency sound insulation performance of the second-order PAM is significantly better than that of the PAM extended structure.Furthermore,it is found that the first-order mass block can inhibit the low-frequency sound insulation of the second-order PAM,while the second-order mass block can promote the low-frequency sound insulation of the second-order PAM.Therefore,a structural improvement method is proposed.By removing the first-order mass and adding the second-order mass appropriately,the lowfrequency sound insulation performance of the second-order PAM can be significantly improved,and the total weight of the structure can be reduced to a certain extent.4)In order to verify the feasibility of the second-order PAM and the correctness of the simulation results,the sound insulation experiment was carried out.The sound insulation tests based on plane wave incidence are carried out in the impedance tube,and the experimental results are in good agreement with the simulation results.In order to evaluate the sound insulation performance of the second-order PAM in the actual installation conditions and the real noise environment,the sound insulation experiments are carried out based on a small box and an anechoic chamber.The experimental results show that the second-order PAM has good sound insulation performance in the real environment and complex sound waves incident.In view of the lack of low-frequency sound insulation performance of local resonance PAM in large size,this paper proposes the design idea of high-order PAM,and carries out the research of low-frequency sound insulation performance of second-order PAM,which provides support and guidance for the practical application of PAM in engineering.