Research Of Acoustic Invisible Devices And Illiusion

Transformation acoustics originated from transformation optics.The main idea is that acoustic wave equation keeps its form under coordinate transformations.The parameter of material distribution of the transformed space can be obtained by the coordinate transformation front-to-back relationships,and acoustic wave manipulation can be realized by using acoustic metamaterials filled in the corresponding space.After the emerging of transformation acoustics,invisible devices and illusion devices have become hot topics of this field.However,it is difficult to complete experiments as the material parameters of the invisible devices and illusion devices are extremely complex.In addition,for the elastic wave equation in general elastic medium,there is no invariance under the coordinate transformations such that transformation elastics is not that easy.How to design the elastic invisible devices with simple methods is also a problem to be solved.Focusing on these problems,we introduce Fabry-Perot resonances based on general transformation acoustics,and design perfect acoustic invisible devices and illusion devices with simple material parameters.In addition,we find the conditions of decoupling the elastic wave equation into longitudinal and transverse waves in general two dimensional elastic medium,and design an elastic invisible device.The main contents of this thesis are as follows:Firstly,theories of transformation optics,transformation acoustic and elastic wave equation are introduced.To simplify acoustic invisible device parameters,transformation acoustics based on the Fabry-Perot resonance principle is proposed.Finally,it is recalled that the elastic wave equation has no invariance under coordinate transformations in general elastic medium.Secondly,invisible devices designed by the general transformation acoustic is difficult to implement as its complex material parameters.In order to solve this problem,based on the general transformation acoustic theory,we innovatively introduced the Fabry-Perot resonance principle,analyze the perfect undetectable acoustic three-dimensional device and reduce the difficulty of the experiment.Next,based on the acoustic invisible devices,we further study the elastic invisible devices.For the purpose of simplifying the design of the elastic cloak,we eventually find that,when the elastic medium satisfies certain conditions,the elastic wave equation could be decoupled into longitudinal and transverse waves in the general two-dimensional elastic medium.Thereby,we achieve an application of elastic conformal transformation invisible device.Finally,inspired by illusion optics,we analytically confirm this illusion elastic effect from Mie theory and Fabry-Perot resonance principle for both two dimensions and three dimensions in a fluid background.Simulations are used to verify the two-dimensional examples,which illustrate that a solid sounds like another in the fluid background.