A Design Method Of Low-frequency Noise Reduction Structure Based On The Acoustic Meta-materials

Low-frequency noise and vibration is characterized by its long penetrating power and long-wavelength characteristics.So,it is difficult for traditional sound-insulating materials to effectively reduce vibration and noise due to the law of mass action.Therefore,it is especially important to broaden the low-frequency bandwidth of structures.In general,vibration control methods have two categories: passive control and active control.The artificially modified acoustic meta-materials realize the integrated design of the structure and the vibration isolation system.In addition,the acoustic meta-materials composed of the artificial micro-structure units can be effectively used to control the low frequencies.The membrane-type acoustic meta-materials can not only satisfy the lightweight requirements,but also achieve effective control of wave propagation by artificially modifying the membrane.So,this meta-materials have important application value in low-frequency noise reduction and sound wave control.Therefore,the research of membrane-type acoustic meta-materials has further guiding significance for the design of low-frequency noise reduction structures for lightweight materials.The research of membrane-type acoustic meta-materials mainly includes the mode of the membrane structure,the band-gap of the unit cell and the acoustic performance,so to analyze the energy change and transmission loss of the structure.The structural form,structural parameters,material parameters,load boundaries,cell distribution and combination forms of the unit cell are critical to the improvement of the sound insulation performance of the material.Based on the principle of the local resonance mechanism,the influence of these parameters on the sound insulation performance of the overall structure is studied under the condition of damping and no damping for the design of the lightweight low-frequency and wide-bandwidth noise reduction structure.In this paper,membrane-type acoustic meta-materials are used to study the design method of low-frequency noise reduction structure.The introduction of mass and damping in the membrane-type acoustic meta-materials,through the periodic array distribution,increases the low-frequency sound isolation characteristics.Firstly,the modal analysis,sound absorption and strain energy distribution simulation of the structure cell were carried out to explore the acoustic properties of the membrane structure.Then,the unit cell of the local resonance acoustic meta-material is established.The band-gap of the unit cell is analyzed byFEM and verified by various calculation methods.Then,the influence of the structure and material parameters of the unit cell on the band-gap is discussed.Adjusting the different parameters,a variety of continuous low-frequency and wide bandwidth unit cell groups are selected.Finally,the low-frequency(0~600Hz)noise insulation characteristics of various finite periodic structures are simulated and the effects of different components of structural unit cells on low-frequency sound insulation are discussed.The results show that the noise isolation characteristics of the membrane-type meta-materials with mass are improved.The larger the difference between the mass and the matrix mass,the larger the band-gap and the single bandwidth;the thickness of the membrane increases,the number of band-gaps is increased but narrow and scattered;the uniform finite periodic structure composed of same unit cells has a limited low-frequency bandwidth by adjusting the unit cell parameters;a plurality of non-uniform finite periods composed of different unit cells can integrate the band-gap of the unit cells by adjusting the parameters and composition forms of different cells.Finally,6 times the bandwidth of 95~550Hz is obtained.