Acoustic Characteristics Of Novel Acoustic Structures Based On Impedance Gradient Materials

In order to solve the numerical instability of transfer matrix method which is used to analyze the acoustic characteristics of the impedance gradient material when the acoustic wave is incident obliquely,in this paper,the return matrix method which is commonly used to analyze the physical properties of layered structures is applied to the numerical simulation of the impedance gradient material.In addition,in order to solve the high initial frequency and narrow band gap of the traditional periodic structure,based on the idea of graded impedance materials,a quasi periodic structure with gradient variation is designed.For impedance gradient materials,an acoustic model with a liquid on the upper surface and a semi-infinite substrate on the lower surface is constructed.Based on the layered idea in calculus and the local coordinate system in geometric measurement,using the wave equation in solid and Hooke's law,the relevant formulas for calculating the acoustic properties of impedance gradient materials by using the return matrix method are derived.For the same impedance gradient material,this method and the transfer matrix method were used to simulate the reflection coefficient of the sound wave under different incident angles,and it was found that the return matrix method has higher stability.Then,the influence of layer number on its stability is analyzed.On this basis,the influence of impedance change curve,acoustic incidence angle and material thickness on the acoustic characteristics of impedance gradient materials is studied.For the periodic structure,a one-dimensional and two-dimensional periodic structure model is constructed.After analyzing the mechanism of the generation of the band gap,the calculation method and the influence of the parameters such as material thickness,cycle number and material impedance on the band gap characteristics,two quasi-periodic structures with uneven thickness and impedance variation are proposed.The influence of thickness and impedance gradient changes on the band gap of periodic structures is analyzed through simulation.On this basis,a quasi periodic structure with gradient variation of impedance and thickness is proposed,the reliability of the design,the influence of the cycle number,thickness and impedance on the band gap characteristics of the structure is analyzed.Finally,three impedance gradient materials,one periodic structure,and five quasi-periodic structures with uneven changes were prepared.Through experiments,the reliability of the return matrix method in the numerical simulation of the acoustic characteristics of impedance gradient materials was verified,the correctness of the designed quasi-periodic structure based on gradient materials,the ability of uneven changes in thickness and impedance to improve the band gap characteristics of the periodic structure,and the effect of different thickness changes and impedance changes on the quasi-periodic structure based on gradient materials are verified.