Research On Sound Absorption Structure Of Durable Rigid Acoustic Metamaterial

In industrial and military environments,most of the noise is in the middle and low frequency bands,and engineering equipment and facilities work under severe environmental conditions such as load-bearing,high temperature,high pressure,and vibration all year round.Traditional porous sound-absorbing materials,such as fiber-absorbing materials and foam sound-absorbing materials,are not suitable for relatively low-frequency sound-absorbing materials because of their poor sound-absorbing effects in low and medium frequencies,poor durability,weak pressure and temperature resistance,and insufficient health and environmental protection.In addition,although traditional cavity resonance sound-absorbing structures(such as hard sound-absorbing perforated plates)can work in more demanding environments,they have insufficient sound absorption capacity in the middle and low frequency bands,and the volume of low-frequency sound-absorbing devices is relatively large.These shortcomings limit the wide applications of the device.Acoustic metamaterials provide new ideas for solving the above problems: the sound absorption performance of acoustic metamaterials may not rely on traditional fibers,foams and other materials,and their sound absorption characteristics can be freely controlled and designed with acoustic subwavelength structures.This method is simple,convenient and can effectively solve the limitations of traditional sound-absorbing materials and sound-absorbing structures,therefore it provides great freedom and flexibility for the research and development of new sound-absorbing materials and devices.In this paper,two types of rigid sound-absorbing devices are designed based on the multi-channel folded cavity structure and slow-wave acoustic metamaterials,and their sound absorption mechanisms,theoretical models,simulation calculations,preparation,processing,and experimental testing have been studied.The main advantages of these new soundabsorbing structures used in harsh environments are as follows:(1)Their sound-absorbing characteristics are mainly determined by their geometric structures,and they can be designed with different functions for line-spectrum narrow-band noise and broadband noise control;(2)A wide range of materials can be selected,and rigid materials such as plastics,metals and ceramics can be used to realize device processing,and they have corrosion resistance,pressure resistance,and the advantages of impact and temperature resistance can be applied to the work requirements of factories,aerospace,military vehicles and marine equipment and other harsh environments;(3)3D printing technology can be used for the processing of acoustic metamaterials,which can achieve high precision,low cost,and batch fabrications of devices.The research work and results of the thesis mainly include the following aspects.First,theoretical model and numerical simulation model of the multi-channel folded cavity is established.Based on these models,an effective theoretical and numerical simulation analysis of the complex acoustic wave-folding cavity interaction is carried out.Development provides theoretical basis and design methods.Through optimized design,the quasi-perfect sound absorption of the folded cavity at the low frequency line spectrum of 230 Hz(acoustic absorption coefficient>0.95)is realized,and the thickness of the structure is only 1/50 of the working wavelength.Furthermore,the series structure of multiple folded cavities realizes the control of multiple resonance absorption peaks in the frequency range of 210 Hz-1500 Hz,which provides new ideas and methods for low-frequency line spectrum noise control technology.In addition,we proposed a wedged slow-wave sound-absorbing metamaterial,and established the theory and finite element simulation model for the slow-wave metamaterial.The relationship between the characteristics was studied,revealing the ultrawideband,high-performance sound absorption characteristics of slow-wave metamaterials.Furthermore,the structural parameters of the wedged slow-wave metamaterial were optimized to achieve a broadband sound absorption effect from 1600 Hz to 5000 Hz.A foldable wedge structure is designed,which can effectively expand the low-frequency sound absorption performance of the device without increasing the overall size of the device.This structure can reduce its lowest sound absorption frequency by at least one octave.