Research On Sound Propagation Characteristics In Materials With Gradient Change Of Impedance

As a typical kind of inhomogeneous material,acoustical medium with gradient properties has received more and more attention.Its composition,physical properties and internal structure exhibit a continuous gradient change,So that the acoustical characteristics and function of the medium are also with gradient change.In order to apply acoustical medium with gradient properties to the attenuation of sound and vibration or the acoustical material design,it is necessary to study and find out the law of sound propagation and the characteristics of sound field in the medium.Based on the theory of layered medium,this paper established the acoustic wave propagation model of the media and discussed the acoustical characteristics of the medium with gradient change of impedance,the periodical composite medium and the structure with the sound asymmetrical propagation respectively.Moreover,the samples of the media were prepared and experiments were implemented.First of all,this paper discussed the sound field characteristics of the multilayer medium when the plane wave obliquely incident,and focused on the variation of the sound field characteristics when the impedance of each layer changed according to some distribution rules.Then the basic relationship between the medium impedance and acoustical performance was established.Secondly,based on the research results on the multilayer composite medium,the acoustical performance of the medium with gradient change of impedance and the periodical composite medium were studied.The inhomogeneous medium with the impedance of continuously gradient distribution was designed,and the calculation formula of acoustical characteristics of medium with impedance of arbitrary distribution was deduced,and the feasibility of the algorithm was validated by simulation.Research on the acoustical properties of the periodical composite medium mainly depends on the band gap calculation,and the band gap properties were studied by varying the geometric parameters and material parameters of the medium.By introducing the medium with gradient change of impedance into the periodical medium,a periodical composite medium was proposed,and its band gap properties were studied.Then the sound asymmetric propagation was realized by using the medium with gradient change of impedance,and the propagation mechanism was further studied,and then the sound asymmetrical propagation effect was evaluated by simulation studies.Finally,the corresponding experimental study was carried out to verify the correctness of the previous theory and simulation research.The medium samples were designed,and their acoustical properties were measured.Then by processing and analyzing experimental data,it was found that the experimental results and the theoretical calculation were in good agreement,which could have provided theoretical and experimental research basis for the engineering application.