Sound Insulation Properties Of New Acoustic Metamaterials And Its Application In Automobiles

With the rapid development of society and economy,people’s requirements for quality of life continue to rise,and noise problems have become prominent and become one of the three major environmental problems.Long-term exposure to noise can easily make people feel irritable and anxious,and affect people’s normal study,work and life.Noise control is a very necessary link in automotive engineering.Automotive acoustic packaging is an important part of the vehicle noise control system,but there is a problem of poor sound insulation performance in the middle and low frequencies(400Hz-800Hz).The emergence of acoustic metamaterials provides new ideas for solving the problem of low-frequency noise,which can be divided into Helmholtz type,thin plate type,film type and so on.Among them,thin-film acoustic metamaterials have the advantages of simple structure,easy fabrication,light weight and small size,and have the potential to be applied to automotive acoustic packaging.In this thesis,thin-film acoustic metamaterials are selected as the research object.The rational application of acoustic metamaterials in automotive acoustic packaging is explored.Through experimental research on thin-film acoustic metamaterials,it is found that it is difficult to apply and control thin-film tension.And the tension film has stress relaxation phenomenon,so that the pretension cannot be maintained for a long time.In this thesis,a rigid thin plate with a large elastic modulus is used to replace the tensioned film,and the concentrated mass is removed to simplify the structure,and two new acoustic metamaterials are obtained.By making samples and testing,it is proved that the new acoustic metamaterial structure can generate sound insulation band gaps at medium and low frequencies.By establishing a simplified model of the structure of acoustic metamaterials,the mechanism of two acoustic metamaterials generating sound-insulating band gaps is analyzed.Based on the finite element method,the acoustic transmission loss calculation models of two metamaterial samples are established.The accuracy of the computational model is verified.Based on the computational model,the vibration characteristics and sound energy of acoustic metamaterials at the peaks and valleys of sound insulation are analyzed.The sound insulation mechanism of acoustic metamaterials was further explored.The effects of the size and material parameters of the acoustic metamaterial element on the sound insulation properties of the acoustic metamaterial are studied.By adjusting the unit size and material,the sound insulation frequency band can be regulated.Based on the finite element method,in view of the difference of experimental results under different sample sizes and boundary conditions,the effects of sample boundary conditions and overall resonance phenomena on the sound insulation performance of acoustic metamaterials are studied.It is found that when the sample size is small,the boundary conditions and overall resonance of the acoustic metamaterial sample will have a greater impact on the overall sound insulation.As the size of the sample increases,the overall resonance frequency of the sample decreases,and the influence of boundary conditions and overall resonance becomes weaker.The sound insulation curve of the acoustic metamaterial gradually approaches the sound insulation curve of the infinite acoustic metamaterial board.Based on the sound insulation test of the reverberation chamber-anechoic chamber window,a reasonable method of applying acoustic metamaterials to acoustic packaging such as engine inner cowl and carpet is studied.When combined with steel plates and soundabsorbing materials to form a double-wall sound insulation structure(steel plate-porous material-acoustic metamaterial),the low-frequency sound insulation advantages of acoustic metamaterials can be well reflected.Compared with the traditional sound insulation structure of equal areal density,the sound insulation performance of the new structure is higher in the middle and low frequencies,but there will be sound insulation valleys in the higher frequency range.Finally,acoustic metamaterials using lightweight materials as frames are fabricated.On the basis of the double wall structure,high-density cotton felt is attached again.On the premise that the total areal density is lower than that of the traditional structure,the new structure still has the advantage of low frequency sound insulation,and makes up for the sound insulation disadvantage of higher frequency band.For the proposed multi-layer plate structure,a calculation model of acoustic transmission loss is established based on the transfer matrix method.The feasibility of this computational model is verified.Based on the calculation model,the effect of porous material layer on the sound insulation performance of the multilayer structure was analyzed.The results of this paper have important guiding significance for the engineering application of acoustic metamaterials and the control of low-frequency noise in automobiles.