Design Of Low-frequency Absorber And Adaptive Sound Absorption System Based On Acoustic Metamaterial

With the development of lightweight design and high-speed development of large-scale transportation equipment such as aerospace vehicles,high-speed trains,automobiles,and ships,the noise problem caused by it is very prominent.Strong noise injures the hearing and health of drivers and passengers and affects the safe operation of instruments and equipment.Therefore,the research and control of the noise of large-scale transportation equipment is an important topic that needs to be solved urgently in the equipment noise reduction project.At present,the use of resonance sound absorption structure to absorb the noise of large-scale transportation equipment is a simple,effective,and widely used method,but there are problems of poor low-frequency sound absorption and insufficient adaptive sound absorption performance.In recent years,the concept of acoustic metamaterials has provided new means for the effective absorption of low-frequency noise.Its acoustic characteristics of small size control large wavelength help the structure to achieve low-frequency noise with a thickness much smaller than the sound wave wavelength at the operating frequency.It is suitable for complex environments such as small spaces and has good application prospects and engineering use-value.Therefore,this paper aims at the problem of low-frequency noise absorption of large-scale transportation equipment and insufficient adaptive sound absorption performance.Based on acoustic metamaterials,the design research of low-frequency sound absorption structure and adaptive sound absorption system is carried out.The main work and research results are as follows:(1)Research on the design of low-frequency absorber structure based on the coupling of micro-slit and coiling-up channel.The two acoustic metamaterials of micro-slit and coiling-up channel are coupled to design,and a low-frequency absorber of micro-slit coiling-up channel is proposed for the first time,its sound absorption theoretical model and numerical model are established.The sound absorption performance,sound absorption mechanism,sound absorption frequency band control law,and sound absorption bandwidth are studied using the impedance analysis method and the graphical method of reflection coefficient complex frequency surface distribution.Finally,the experimental samples were designed and processed for experimental test verification.The research results show that the designed absorber has excellent low-frequency sound absorption performance,and can achieve nearly perfect sound absorption of 137 Hz under the deep sub-wavelength structure thickness of ?/85.The structure is rich in adjustability,and the sound absorption frequency band can be adjusted by changing the width of the micro slits and the number and width of the coiling-up channels.The relative sound absorption bandwidth of the structure is broadened from 39% to 54% by parallel connection.The experimental measurement results are good,which proves the correctness and feasibility of the designed absorber.(2)Research on the design of low-frequency broadband absorber based on micro-perforated plates.By optimizing the sound absorption bandwidth of a single absorption peak and introducing a second-order absorption peak at low frequencies,a low-frequency broadband absorber is designed based on the micro-perforated plate.The sound absorption theoretical model and numerical model are also established.Impedance analysis and the graphical method of reflection coefficient complex frequency surface distribution are studied on its low-frequency broadband sound absorption mechanism,sound absorption frequency band regulation law,and sound absorption bandwidth.Finally,carried out experimental verification.The research results show that the designed structure has double absorption peak absorption characteristics and excellent low-frequency broadband sound absorption performance.Among them,the absorber 1,at the sub-wavelength scale of ?/15,has a relative sound absorption bandwidth of 152%,in the 258-815 Hz frequency band.The internal average absorption coefficient is 0.82,the absorber 2,in the sub-wavelength scale of ?/12,the relative sound absorption bandwidth is 159%,and the average absorption coefficient in the 295Hz-945 Hz frequency band is 0.83,The relative sound absorption bandwidth of absorber 1 and absorber 2 in parallel is 172%,and the average absorption coefficient in the 258Hz-936 Hz frequency band is 0.87.The experimental measurement results are well,which proves the correctness and feasibility of the designed structure.(3)Research on the design of adaptive sound absorption system based on micro-perforated and micro-slit.Based on the principle that the resonance sound absorption frequency of the micro-perforated and micro-slit absorber is controlled by the height of the back cavity,an adaptive sound absorption system was developed and designed using a combination of active and passive sound absorption.Completed the design of the system's adaptive sound absorption structure,data acquisition system,control system,and drive system,and conducted simulation test research.An experimental test platform for the adaptive sound absorption system was built and an adaptive sound absorption verification experiment was carried out.The research results show that the designed adaptive sound absorption system can perform autonomous noise identification within the range of 224Hz-818 Hz,automatically adjust the height of the back cavity of the sound absorption structure,change the resonance frequency of its own resonance,and achieve adaptive and effective absorption of target noise.