The Research On Sound Insulation And Noise Reduction Based On Gradient Metamaterial Plate

The good performance of NVH(Noise, vibration, Harshness) is an important target of automobile comfortab leness, and has been gradually taken seriously by users and automobile manufacturers. Now, looking for a convenient and low consumption vibration noise reduction scheme is the focus of the manufacturers. Lamb wave acoustic metamaterial has been increasingly of greater interest to many researchers in recent years. The energy of Lamb wave completely localized on board up and down between the free surfaces of metamaterial plate, which greatly reduced energy consumption in the process of elastic wave propagation. The application of acoustic metamaterial not only can generate elastic wave s band gap, elastic wave can’t propagate when the frequency located in forbidden band, but also can realize asymmetric transmission of elastic waves, has a very good rectifying effect. This paper studies the noise reduction features of finite gradient periodic structure slab, and then realize the first-order Lamb wave asymmetric transmission through mo del transformation mechanism in gradient plates, finally discussed the feasibility of noise and vibration control in engineering structures by the gradient metamaterial slab. The main research work is shown as following:(1) Eigen-mode matching theory(EMMT) method and finite element method(FEM) are used to calculate the transmission spectrum of finite gradient periodic structure slab, respectively. We found that the transmission spectrum calculated by EMMT method is in good agreement with the results by FEM, and there are band gaps in the finite gradient periodic structure slab. Subsequently, we analyzed the connection and differences between the finite gradient periodic structure slab and finite periodic structure plate.(2) Based on the original model, the impact of the structural parameters on the position and width of the band gap is studied by adjusting width ratio and thickness in both ends of the finite gradient periodic structure slab.(3) We studied the first-order antisymmetric Lamb wave asymmetric transmission in gradient plate. We calculated the transmissivity of forward and reverse incidence by EMMT method, and we found that there is an obvious phenomenon of asymmetric transmission. Then, the finite element software COMSOL Multiphysics is used for the time domain analysis, the mechanism of asymmetric transmission is discussed in detail, which namely the Lamb wave mode conversion mechanism.(4) We calculated the first-order antisymmetric Lamb wave asymmetric transmission contrast ratios of the angle and height of gradient plate changing, the angle is the main factor that effect asymmetric efficiency, and the change of gradient plate thickness has important influence on working frequency range of asymmetric transmission.