Tunable Membrane-type Acoustic Metamaterial Based On Magnetic Field Control And Its Low-Frequency Sound Insulation Performance

Low-frequency noise has the characteristics of strong penetrating ability,long propagation distance,and low attenuation.Effective control of low-frequency noise has always been one of the difficulties in the field of acoustics research.Acoustic metamaterial is a kind of periodic composite material with negative equivalent characteristics in the sub-wavelength range,which can realize large-scale structure control of large-wavelength noise.Therefore,acoustic metamaterial has unique engineering application value in the field of low-frequency vibration reduction and noise reduction.In this paper,a tunable membrane-type acoustic metamaterial structure based on magnetic field control is designed.A variable-strength axial uniform magnetic field loading device is designed and fabricated.For the first time,membrane-type acoustics is realized under the action of axially active adjustable magnetic field.The non-contact active tuning of the acoustic properties of metamaterials broadens the control bandwidth of acoustic metamaterials for low frequency noise,and through theoretical calculation and analysis,finite element simulation and sound insulation experiments under axially adjustable uniform magnetic field.The changes in sound insulation characteristics were analyzed and studied in detail.The main research contents and work are as follows:1.A tunable membrane-type acoustic metamaterial structure based on magnetic field control is designed.magnet is fixed on the center of the membrane,and the electromagnetic force is applied to the magnet by an axial magnetic field loading device capable of generating a uniform magnetic field.The input current can change the electromagnetic force acting on the magnet,thereby changing the equivalent parameters of the acoustic metamaterial structure,and finally achieving the non-contact active tuning of the acoustic properties of the acoustic metamaterial.Based on the local resonance mechanism,the theoretical model and structural model of the active acoustic metamaterial are established.The finite element software is used to analyze the sound insulation characteristics of the model under the action of axial uniform magnetic field.The results show that: Under the excitation of a uniform magnetic field,the acoustic characteristics of the structure and the magnetic field do not change significantly.As the input current intensity increases,the structural acoustic peak corresponds to the frequency shifting toward the high frequency,effectively widening the structural sound insulation control range.Non-contact active tuning of the acoustic properties of acoustic metamaterials.2.The influence of the geometric parameters of the model structure on the acoustic isolation characteristics of active acoustic metamaterials is studied.The effect of changing the thickness of the membrane or changing the mass of the additional magnet on the controllable properties of the active acoustic supermaterial under the same axial magnetic force was studied.The results show that: increasing the thickness of the membrane makes the structural sound insulation peak shift to high frequency,effectively widening the structural sound insulation bandwidth,widening the sound insulation frequency control range under the axial magnetic force,and increasing the additional magnet mass to make the structural sound insulation peak shift to the low frequency,effectively improve the initial low frequency sound insulation effect of the structure.3.The effects of material parameters of the model structure and membrane prestress on the acoustic insulation properties of active acoustic metamaterials were investigated.The effect of changing the Young's modulus of the film or changing the prestress of the film on the sound controllability of the active acoustic metamaterial under the same axial magnetic force is studied.The results show that increasing the Young's modulus or pre-stress of the membrane makes the structural sound insulation peak move to high frequency,and at the same time,it has a significant influence on the sound insulation control performance of the structure under the axial magnetic field,and widens the axial magnetic force.The acoustic frequency control range enables structural acoustic performance to achieve contactless active tuning over a wide frequency range.4.The sound insulation test platform was built to analyze the sound insulation characteristics of the active acoustic metamaterial.The existing acoustic measurement system was improved,and an acoustic test system with an axially adjustable uniform electromagnetic field loading device was designed and prepared.The experimental specimens of active acoustic metamaterials were prepared.The impedance test of the active acoustic metamaterials was tested by the impedance test system based on the four-sensor method.The experimental data and the finite element software simulation data were compared.The results show that: The tunable membrane-type acoustic metamaterial structure based on magnetic field control designed in this paper has good lowfrequency sound insulation controllability,and can realize non-contact active tuning of structural sound insulation characteristics.