Artificial Impedance Surfaces and Wire Media for Absorption and Cloaking.

摘要

The main objective of this dissertation is to investigate the ability of utilizing artificial impedance surfaces and wire media for absorption and cloaking applications. The dissertation includes two parts which focus on the electromagnetic wave propagation in absorbers formed by stacked metasurfaces and structured wire media, and electromagnetic wave interaction with the cylindrical cloaking structures.;In the first part, we propose a variety of physical systems that show multiband and wideband absorption properties in the microwave regime. For the multiband absorbers, we propose a simple analytical model to study the absorption properties. Further, using the same circuit model, the physical mechanisms of the observed behavior is clearly explained in terms of the open/coupled Fabry-Pérot resonators. To design wideband absorbers, we first analyze a single-layer wire medium loaded with an arbitrary material (a thin copper patch with finite bulk conductivity and a graphene patch characterized by its complex surface conductivity) at one end and a ground plane at the other. Based on the properties of the single-layer structure (which acts as a narrowband absorber), we next propose a novel multilayered mushroom structure with thin resistive patches at the wire-medium junctions for wideband absorption. To characterize the wideband properties, here, we derive new additional boundary conditions and solve the scattering problem using an analytical model developed particularly for the problem at hand. We also show a methodology to design these absorbers and explain the wideband absorption mechanisms.;The second part focuses on the application of various metasurfaces for cloaking dielectric and conducting cylinders for plane-wave incidence and for line sources in close proximity. The cloaking mechanism is based on a mantle cloaking technique, wherein the scattered field produced by the object is cancelled by the cloak. The purpose of this work is to design the mantle cloaks using the metasurfaces, to render the objects invisible. The analysis here is carried out using a rigorous analytical model which employs the Lorenz Mie-scattering theory. Two-sided impedance boundary conditions are applied at the interface of the metasurfaces and analytical grid-impedance expressions derived for the planar cases have been successfully used in tailoring the reactances of the cylindrical surfaces. Further, the analytical results presented in the dissertation are verified using the numerical simulations.