Structural Design Of Membranecavity Coupled Acoustic Metamaterial And Study On Its Absorption Performance

Noise exists in all aspects of production and life,which has adverse effects on people's physical and mental health and the reliable operation of equipment.In particular,low-frequency noise has strong penetration and is difficult to be effectively isolated and absorbed,which has always been a problem in the field of noise reduction.This paper focuses on the design of acoustic metamaterials and studies the low frequency sound absorption performance of membrane-cavity coupled acoustic metamaterials by means of theory and simulation.First,design a new type of massless membrane-cavity coupled acoustic metamaterial structure,and based on the finite element method and acousto-electric analogy method,the simulation model and equivalent circuit of the multi-physics coupled of the structure are established respectively,and the sound absorption coefficient is introduced as the evaluation standard of the sound absorption performance of the structure.The sound absorption curve obtained through the experimental test is in good agreement with the simulation and theoretical model,which verifies the correctness of the simulation and theoretical model.Secondly,the acoustic energy loss of each part of the structure is studied,and the results show that the air layer contributes the most to the acoustic energy loss.It is further proved by the complex frequency plane that the perfect sound absorption of the structure is due to its critical coupling state,and the perfect sound absorption is due to the perfect match between the surface impedance of the structure and the characteristic impedance of the air.Finally,the influencing factors of the sound absorption performance of the structure were explored,and it was found that the membrane density and thickness,the perforation radius and the depth of the back cavity have a greater influence on the sound absorption performance of the structure,and especially pointed out that the structure due to the introduction of back cavity,surface tension within a certain range of change,will not affect sound absorption performance,This shows that the structure does indeed reduce the dependence on the membrane tension.In order to achieve the research goal of low frequency and broadband,firstly,carry out the design of the multi-layer membrane-cavity coupled structure,and use the transfer matrix method to establish the theoretical model of the multi-layer structure.In order to improve the acoustic performance,the spiral structure is introduced into the multi-layer structure,and genetic algorithm is used to optimize the design.The optimization parameters take into account the impact on the sound absorption performance of the structure and the actual situation.The perforation radius and the depth of the back cavity are selected,and the spiral line growing coefficient and total length.The optimized composite three-layer structure can maintain the sound absorption coefficient above 0.8at 300-550 Hz when the thickness is 52.5 mm.The comparison experiment results verify the correctness of the optimization results.Secondly,the parallel design of the membranecavity coupled structure is studied.First,the perforation form of the parallel unit is improved.It is found that the introduction of variable cross-section and mutation crosssection intubation can significantly improve the low-frequency acoustic performance of the structure.Secondly,based on the coherent coupling between the parallel units,the design of the parallel structure is carried out for three different perforation forms and composite three-layer units.The through-hole parallel structure is at 320-600 Hz,and the variable cross-section type is at 225-350 Hz.The mutation cross-section-intubation type maintains a sound absorption coefficient above 0.8 in the range of 180-240 Hz,and the thickness of the three parallel structures is 42.5 mm.The two parallel structures of the composite three-layer unit have sound absorption coefficients higher than 0.5 and 0.8 in the range of 260-900 Hz and 300-620 Hz,respectively,and the structure thickness is 59.5mm and 44.5 mm,respectively.Finally,a square impedance tube acoustic test system was built,the parallel structure was tested,and the sound absorption curve was obtained by using the transfer function method.