Study Of Thinabsorbing Structures Using Metamaterials

With the development of modern technologies, microwave absorbing materials are becoming important in both military and civil applications. An absorbing material is a kind of functional material that can absorb most power of the incident wave and yield little reflection. The material with such properties is in great demand in industries exposed to electromagnetic pollution, such as broadcasting and TV, electrical power, medical equipments and telecommunication, and so on. The absorbing material with thin thickness, light weight and wideband absorbing performance is most expected and being widely studied.This thesis first deals with the mechanism of the interaction between electromagnetic waves and absorber, then tries to work out a novel thin microwave absorber but with considerate absorbing bandwidth, based on the single-layer form of a classical absorber, named Salisbury screen. Electric Salisbury screen is easy to prepare but it has to be 1 4λ_g thickness to realize absorption. It has been demonstrated that ifwe closely place a high-impedance surface (HIS) above a perfectly conducting plate with a resistive sheet on the top of this surface, and then we can achieve a thin structure that can be an efficient sheet absorber for incident electromagnetic energy. A HIS can be effectively realized by using a planar electromagnetic bandgap (EBG) structure with metal and dielectric composite.Based on the concept introduced above, the HIS surface is composed of a period of flat square metallic patches with a Jerusalem cross slot (JCS) in each patch. Chip resistors of proper resistance value were loaded between the patches to dissipate incident energy and function as impedance matching with free space to minimize reflectivity. The simulation results show that the resonant frequency of the absorber is only determined by JCS, and its reflectivity reached the lowest point at reflection phase zero point. The influences of various structure parameters of JCS on the absorption characteristics are analyzed to provide guidance on theoretical design for practical application. The sample of JCS was fabricated. The validation and effectiveness of the proposed JCS design are conducted by using waveguide simulation and measurement.Based on metamaterial absorber proposed by Landy, this thesis researched the absorbing principle of an absorbing structure composed of symmetric split ring (SSR) and short wire. The overlap of different absorbing bands is utilized to achieve the design of broad band absorber by adjusting the parameters of SSR suitably. Furthermore, this thesis proposed a nonsymmetric split ring (NSSR) to design multiband absorbing structures. By optimal design, the dual-band and triband absorbing structures can be realized by combining two separate nonsymmetric SSRs with two separate short wires.