An Acoustic Metamaterial Based On Helmholtz Cavity And Membrane And Research On Transmission Loss In Low Frequency

Acoustic metamaterial is one of the research focus in the field of acoustics,as its negative special material properties include negative density and modulus which the other materials don't possess.Acoustic metamaterial is a kind of periodic sub-wavelength synthetic composite material or structure.Acoustic metamaterial can control longer wavelengths of acoustic wave with small sizes.Therefore,acoustic metamaterial has wide application prospect in the field of vibration and noise reduction in low frequency.In this paper,we design and fabricate an acoustic metamaterial based on a Helmholtz resonator coupling with thin membrane by the theoretical calculation,numerical simulation analysis and experimental verification,the main study contents are as follows:1.Design an acoustic metamaterial based on Helmholtz resonator coupling with thin membrane,the metamaterial composes of a split hollow opened at the top of a cylindrical cavity and a thin membrane.The acoustic metamaterial geometric model is established and the sound insulation performance is analyzed using finite element software.The transmission properties and pressure field distribution of the structure with thin membrane cylindrical cavity acoustic metamaterial and without membrane structure are compared and analyzed in low frequency range.2.The influence of geometric parameters on the the sound insulation performance of the designed acoustic metamaterial structure is Studied,the geometric parameters of the structure are optimized and achieve the effect of low frequency broadband optimization.Keep other geometric parameters constant and change the parameters of a certain geometric parameter to calculate transmission coefficient curve minimum value,the corresponding frequency and the frequency width which corresponding to the transmission coefficient lower than 0.6.The height of the cavity,small hole depth and radius,the thickness of the membrane and the height of cavity up to the membrane and the height of cavity down to the membrane are the main geometric factors to be studied.3.Acoustic metamaterial structures are scheduled to use the impedance tube to measure the transmission loss.Through the four-microphone method to calculate the sound transmission lossof the kinds of the two structures.Experiment result shows that experimental measurement results and the numerical simulation results keep consistent trends.Experimental results verified the designed acoustic metamaterial has a good sound insulation performance.4.The designed experiment sample was divided into some layers and layers can be assembled structure,so it can change the geometric parameters of the structure by changing the sample layers and study acoustic metamaterial transmission characteristics by changing the structure geometric parameters.For the membrane,it is studied that prestress and mass blocks pasted on the membrane change the sound transmission loss of the acoustic metamaterial structure in the low frequency.The influence of structural geometric parameters,thin-membrane prestressing and pasted mass blocks on the quantity of acoustic metamaterial sound insulation is analyzed.And the optimal sound insulation performance of the acoustic metamaterial structure is achieved.