Research Of Material Parameters Inversion Based On Reflection

The traditional method for measuring the gradual change of impedance gradient of impedance graded change sound absorption material will not only damage the material,but also have a low efficiency and a large amount of work.Therefore,this paper presents a method by acoustic measurements without destroying the material,and inverse the variation law of acoustic parameters inside of the impedance graded change sound absorption material through reflection coefficient.The inversion physical model is obtained first before the inversion the parameters of impedance graded change sound absorption material,and then using an efficient inversion algorithm,by linking the measured data to the physical model through the cost function,and then complete inversion of the variation law of acoustic parameters inside the inversion impedance graded change sound absorption material.Therefore,the wave equation in inhomogeneous medium and its analytical solution under the condition of specific parameter distribution are derived,and its approximate solution is obtained by WKB approximation and layered theory.The wave field in inhomogeneous medium with given sound velocity and density distribution is simulated by analytical solution and approximate solution respectively,and the consistency of the two solutions is verified.On this basis,the physical model of the parameters of the impedance graded absorption material is established.In order to study the effect of impedance variation on the reflection characteristics of impedance graded absorption material,the loss coefficient distribution is a constant in the medium,the velocity and density distribution of different variation and the velocity and the density distribution is a constant in the medium,the loss coefficient distribution of different variation are simulated respectively Through the comparison,we find that the loss coefficient should be increased larger with the thickness under the conditions of the surface parameters of impedance graded absorption material are similar to those of water,but the change can not be quickly,because when the speed of sound,density or loss coefficient changes too fast will inevitably lead to impedance mutation,which can damage the impedance matching.The wedge-shaped absorption structure commonly used in anechoic pool or anechoic chamber is a kind of typical impedance graded sound change absorption structure,therefore,the reflection model and sound absorption mechanism of the wedge-shaped absorption structure are also studied emphatically,And the influence of wedge length on the sound absorption performance were studied.In the research of inversion algorithm,the effectiveness of traditional Monte Carlo inversion algorithm andsimulated annealing inversion algorithm are compared.Simulation results show that in the multi-parameter inversion of complex model,the simulated annealing inversion algorithm is superior to traditional Monte Carlo inversion algorithm.Finally,the reflection coefficient of multiple wedge samples was measured experimentally in water acoustic tube,and the parameters of wedge medium were retrieved by simulated annealing algorithm.The results show that the acoustic parameters can be obtained by measuring the reflection coefficient and the effective inversion algorithm.