Metamaterials for enhanced light control: from high resolution focusing to invisibity
Acceso abierto / Sarbide irekia
Trabajo Fin de Máster/Master Amaierako Lana
Artificial dielectrics and their descendants – metamaterials, have unusual electromagnetic parameters and provide more abilities than naturally available dielectrics for control of the light. The first experimental realization of a double negative medium gave an enormous impulse for research in the field of electromagnetism. As result, a lot of fascinating electromagnetic devices have been develo ... [++]
Artificial dielectrics and their descendants – metamaterials, have unusual electromagnetic parameters and provide more abilities than naturally available dielectrics for control of the light. The first experimental realization of a double negative medium gave an enormous impulse for research in the field of electromagnetism. As result, a lot of fascinating electromagnetic devices have been developed since then, including metamaterial lenses, beam steerers and even invisibility cloaks. The aim of this master thesis is to contribute to the development of such devices, especially metamaterial lenses and invisibility cloaks. First, a background of metamaterial and metasurfaces is introduced. The main aspects of metamaterials and their characteristics are reviewed, so that the working principles of metamaterials can be acquired with minimal prerequisite mathematics. Then we review the design process of several metamaterial lenses, including a zoned fishnet metamaterial lens and a Soret lens, a member of Fresnel zone plate lenses. Finally we design a carpet cloak, using a metasurface with double ring resonators. In the first application, the time-honored zoning technique is used to reduce the volume, and therefore weight, of a fishnet metamaterial lens. By properly optimizing a profile of the zoned lens we are able to reduce a volume of the lens up to 60% and broaden the fractional bandwidth up to 3 times. With this optimization technique the bandwidth of the zoned lens, which usually is narrow band, increases without causing any deterioration in its performance. The second metamaterial lens is a member of the well-known Fresnel zone plate’s family and consists of alternating and opaque concentric rings. Since half of the power is blocked by opaque rings the efficiency of such lenses is low. In order to improve the coupling and illumination efficiency we propose using an array of subwavelength holes instead of the transparent ring. Also by supporting the lens with a block of fishnet metamaterial working in near-zero index regime it is possible to improve radiation characteristics of a metalens antenna, such as directivity and side lobe level. Finally, in the third application a ground cloak design is described as simulation results. The presented ground cloak is based on a metasurface, an array of closed ring resonators, and, therefore, has an ultrathin design and relatively simple in fabrication. The proposed cloak has been successfully employed to conceal an electrically large object (1.1λ0) for wide range of incident angles and relatively wide frequency range. [--]
Máster Universitario en Comunicaciones / Unibertsitate Masterra Komunikazioetan
The author acknowledges Spanish Ministerio de Economía y Competitividad for the financial support (under grant FPI BES-2012-054909) of his study at UPNA.