The Study Of Superscatterer And Its Applications On Designing Metamaterial Device

Metamaterials are artificial composite materials that display properties be-yond those available in naturally occurring materials and give enormous choice ofmaterial parameters for electromagnetic applications. Transformation media con-cept provides an e?cient way to design various functional electromagnetics(EM)devices. In this dissertation, we first propose the concept of"superscatterer"based on the transformation optics and the complementary media theory andmake detail investigation on the scattering behaviors of superscatterer and showa few typical applications, including hidden portal, invisible open cloak, etc.Then, we investigate the acoustics metamaterials. We not only give the layeredmethod to realize the reduced acoustic cloak, but also prove the existence ofacoustic superscatterer by means of rigorous scattering theory. At last, we studya special acoustic metamaterial—phononic crystals(PCs), which is composed ofdi?erent 2D lattice structure in unit slab. The concept of"superscatterer"hasgreatly enriched the study of functional devices for metamaterials and provide avast research area for the practical applications of EM and acoustic waves. Thewhole dissertation is organized as follows.In chapter I, we described the background and reviewed the current researchprogress in this area. The related theories and concepts, including the causeof negative refractive index, transformation optics and complementary mediaconcept were brie?y showed in chapter II.The content of Chapter III is the major part of our work. First, comparedwith the optical devices of invisible cloak, we designed a di?erent EM device called"supscatterer". When we put a special NIM(negative refractive index material)shell on a PEC(perfect electric conductor), the scattering property of this deviceis equivalent to a"virtual"PEC whose scattering cross section is much bigger than the device itself, and the space between the original PEC and virtual PECseems to be removed. In fact, according to the concept of complementary media,the removed space is filled with a pair of complementary media: vacuum andNIM shell. Similar concept can be extended to the case of non PEC. Then, bymeans of the superscatterer, we proposed a design of hidden portal in which theentrance is concealed from the EM wave detection, however the small objectscould pass in and out freely. This design can be as a physics interpretation ofplatform 934. Third, we proposed a perfect invisible open-cloak. There are no anyinformation communications between the inner and outer domains in traditionalinvisible cloak since the object is closed in the cloak shell. Due to the impedancematched in every interface, the open-cloak with gap in cloak shell not only makethe object perfectly invisible, but also keep contact with the outside world. Atlast, we brie?y described the characteristics of deformation and location shift byextending the concept of supersatterer. As the name of deformation suggests,an object with certain shape coated with suitable NIM shell would transforminto another one with di?erent shape. Another application called displacementshift shows the phenomenon which one sees an object somewhere but in factthe real location is not here. These two visual illusions are the straightforwarddevelopment of the concept of superscatterer.Chapter IV is another part of our work. We discussed some applications oftransformation media in acoustic ?uid. In addition, the acoustic superscattereris designed and the distributions of pressure field are also investigated in detail.For the purpose of fabrication in experiment, we proposed a multi-layered sys-tem method which is composed of concentric layered structure with alternatinghomogeneous isotropic materials. We also found that this design can avoid thelarge pressure inside the device.Next, a relatively independent work about the scattering properties of PCs( phononic crystals ) is shown in chapter V. From the the layered MST(multiplescattering theory) in PCs with simple lattice structure, we developed a methodto investigate the"complex"lattice structure PCs. The new method is inspiredby the surface analysis in LEED ( low energy electron di?raction ) where weexpanded the di?erent 2-D reciprocal lattice vector of layers in a new introducedcommon lattice. With this new method, the propagation characters of elastic waves in the rational related structure PCs, i.e., complex PCs, is calculated andwe found some special behaviors, such as band gap from Bragg scattering andlocal resonant properties at low frequency.The last chapter gave the conclusion and outlook of this dissertation.