Investigations Of The Active Acoustic Metamaterial With Electromagnetically Frequency-tunable And Low-frequency Sound Insulation Performance

Noise control at low-frequency have been research hotspots and difficulties because of its long wavelength,slow attenuation,long propagation distance,and strong penetrating ability.Acoustic metamaterials,as a periodically arranged composite structure,can absorb lowfrequency sound waves through the design of sub-wavelength-scale structures,and have broad application prospects in the field of low-frequency noise and vibration reduction.In order to broaden the sound insulation bandwidth of acoustic metamaterials at low-frequency and realize active control of sound insulation,in this paper,an active acoustic metamaterial with sandwich membrane structure is designed and prepared.By controlling the current-carrying intensity of the axial magnetic field generator,the membrane tension can be adjusted and controlled.Using theoretical analysis,COMSOL simulation and acoustic experiments,the sound insulation and control characteristics of acoustic metamaterials under electromagnetic tuning devices are studied.The main contents of the research are as follows:1.An iron powder-silicone rubber sandwich membrane structure with electromagnetically tunable tension and mechanical properties is designed and prepared.The iron powder-silicone rubber sandwich membrane has the advantages of soft elasticity and ferromagnetism.Appropriate electromagnetic force can change the tension of the sandwich membrane and effectively adjust the mechanical properties of the sandwich membrane structure.The density,elastic modulus,Poisson's ratio and other mechanical properties of the sandwich membrane structure were measured and analyzed by weighing method,tensile test and DIC experiment,which laid the foundation for the design of acoustic metamaterials,simulation analysis and sound insulation experiments.2.An active acoustic metamaterial structure with electromagnetically frequency-tunable are designed.The structure is composed of a carbonyl iron powder-silicone rubber sandwich membrane,an additional lead mass,a fixed frame and an axial magnetic field generator.According to the local resonance mechanism,the theoretical model of acoustic metamaterial is established.Using the finite element software COMSOL,the natural frequency and mode of the structure,and the sound insulation control of the acoustic metamaterial under electromagnetic force tuning were analyzed.The results show that the current-carrying intensity of the axial magnetic field generator can be effectively changed by controlling the axial magnetic field generating device.The new acoustic metamaterial broadens the low-frequency sound insulation bandwidth of the structure and realizes the active control of the sound insulation effect.3.The influence of the dimensional parameters of the structure(the mass of lead,the thickness of iron powder-silicone rubber sandwich membrane)on the acoustic performance and control ability of the new acoustic metamaterial was studied.The results show that the sound insulation peak frequency of the structure moves to low frequency with the increasing of the mass of the lead.With the increase of the thickness of the iron powder-silicone rubber sandwich membrane,the sound insulation peak frequency of the structure move to high frequency.In this study,the structure,with the lead radius is 4mm,the height is 4mm,and the thickness of the sandwich membrane is 1.1.mm,can realize active tuning of sound insulation and effectively broaden the bandwidth of low-frequency sound insulation.4.The influence of the structural material parameters(Young's modulus and prestress of the iron powder-silicone rubber sandwich membrane)on the acoustic properties of the new acoustic metamaterial is studied,The results show that the sound insulation peak frequency of the acoustic metamaterial moves to high frequency when the iron powder-silicone rubber sandwich membrane have the higher Young's modulus or the greater prestress,.In this study,from the measure results,when the Young's modulus of the sandwich membrane is 3MPa and the prestress is 10 MPa,the acoustic metamaterial can effectively broaden the low-frequency sound insulation bandwidth and realize active control of sound insulation.5.An experimental platform is set up to conduct a detailed study on the acoustic performance of the new acoustic metamaterial.A special electromagnetic coil winding machine and an axial magnetic field generator is designed and prepared,and the traditional impedance tube is improved into an acoustic measurement system with an electromagnetic adjustment device;The acoustic metamaterial samples with an iron powder-silicone rubber sandwich membrane structure were prepared,and were studied by the improved acoustic measurement system with a four-position sensor method.The research results show that the maximum movement of the peak frequency of the electromagnetically tunable membrane acoustic metamaterial is 88 Hz,which achieve good sound insulation and active tuning effects in the low-frequency range.The experiment verifies the theoretical analysis and simulation results.