Wire media for broadband enhancement of radiation and power transfer

Abstract

Presented thesis is focused on the wire media applied for enhancement of the dipole radiation. Wire medium is a metamaterial that has seen a lot of interest due to the hyperbolic frequency dispersion and the strong spatial dispersion that does not vanish even in the quasi-static limit. A combination of these exotic properties observes in no one natural material and even in chemically synthesizable materials it is hardly possible to engineer. Meanwhile, creating new devices demands artificial materials with more and more unusual properties. Previously, it was proved theoretically and experimentally, that the evanescent spatial spectrum of the dipole source radiation efficiently converts into propagating waves if the dipole is placed inside the infinite wire medium. Thus, it is possible to extract efficiently the radiation from the separate inefficient sources or areas of distributed poorly radiating sources. However, the finite size for any physical object including any sample of a wire medium hinders the implementation of this enhancement for practical applications due to almost total internal reflection. This effect also hinders the use of wire media for broadband transfer of power. The implementation of the broadband enhancement of radiation and broadband power transfer becomes not so easy, it requires a modification of the wire medium samples and imply many scientific questions, which I tried to answer in this thesis. Among these questions, three are the main ones, corresponding to three different types of the finite-size wire-medium samples dedicated for the broadband enhancement of radiation and power transfer that we aim to achieve beyond any capacitive, inductive or galvanic coupling of the radiating dipoles with the wires. The first one is a wire medium-based hyperlens, which answers the question about the possibility to surpass drastically the blackbody limit for thermal radiation in a wide frequency range. I show how the divergence of metal wires and other design parameters of the hyperlens modifies the radiation of a dipole into free space offering its huge broadband enhancement. The second type of wire media are samples with parallel alignment of the wires. They are not suitable for the broadband enhancement of the embedded dipoles but answer the question is it possible to transfer the power over a wide frequency band across a wire-medium sample. It is possible if the interfaces of a wire-medium slab slightly submerge into two media or are inserted into two hollow waveguides. The third topic refers to a new type of wire metamaterial – irregular wire media – arrays with small but random tilt of the wires. This metamaterial allows a broadband enhancement of radiation, and, in contrast to a hyperlens, answers the question is it possible to achieve this effect without the enlargement of the radiating aperture.