Study On Low Frequency Muffling Technology Of Flexible Acoustic Metamaterials

The low frequency noise radiation level is an important factor affecting the stealth performance and ride comfort.Due to the strong sound-transmission ability of low-frequency noise,it is difficult to effectively control the traditional noise reduction materials,but acoustic metamaterials can realize good control of low-frequency noise due to the unique subwavelength structure.In order to solve the low frequency noise control problem of high speed car with low vacuum pipeline,this paper,based on the actual application conditions,combines flexible materials with Helmholtz resonant acoustic metamaterial,proposes a flexible material of Helmholtz resonant acoustic metamaterial,and studies the acoustic performance and influencing factors of flexible acoustic metamaterial by combining simulation calculation and experimental verification.The main work contents are as follows:Firstly,the sound insulation mechanism of acoustic metamaterial theory is analyzed,and the evaluation index of transmission loss is derived.According to the design theory and simulation analysis of Helmholtz resonator,the structure of flexible acoustic metamaterial is designed in combination with the frame structure of car door.The simulation results show that the designed flexible acoustic metamaterial has a resonance peak at 175 Hz,showing obvious Helmholtz resonance effect,and the noise attenuation effect is obvious in low frequency band.The flexible material design enhances the noise attenuation characteristics of the acoustic metamaterial in the middle and high frequency band.Secondly,the acoustic performance of the acoustic insulation panels before and after the installation of the flexible acoustic metamaterial is simulated and compared by using the actual noise excitation conditions.The results show that the transmission loss of the acoustic insulation panels can reach 70 d B at 175 Hz after using the flexible acoustic metamaterial.In the low frequency noise range of 100-250 Hz,the noise transmission loss after the installation of flexible acoustic metamaterial is 20 d B higher than that without the installation,which further demonstrates the advantages and feasibility of the application of flexible acoustic metamaterial.In order to widen the low frequency anechoic band of flexible acoustic metamaterials,the influence of the change of neck diameter and cavity volume on the transfer loss of flexible acoustic metamaterials was investigated.Finally,according to the structure size of the flexible acoustic metamaterial,the processing technology and pouring mold were designed,and the sample of the flexible acoustic metamaterial was prepared by partial drawing method.The acoustic performance test platform was built to test the designed flexible acoustic metamaterial.The transfer loss of the flexible acoustic metamaterial was measured by the double load method to verify its low frequency noise reduction performance.The final experimental results are consistent with the simulation results.The designed flexible acoustic metamaterial has a good low frequency noise attenuation effect,reaching the resonance peak at 175 Hz,and the peak loss of low frequency transmission can reach 40 d B.By changing the cavity volume,the resonance frequency is shifted from 175 Hz to 205 Hz,and the offset reaches 30 Hz.At the same time,the flexible structure keeps the transmission loss of 25 d B in the middle and high frequency band,which guarantees the noise reduction performance,and lays the foundation for the engineering application of flexible acoustic metamaterials in high-speed flying trains.