Year: 2019
Type: dissertation
Abstract: This thesis explores engineering of the scattered wavefronts, from microwaves to optics, with metasurfaces comprising arrays of polarizable, subwavelength-sized particles. The scalar and tensorial aspects of wavefront manipulation are considered based on four novel metasurfaces. The aim of the scalar wavefront manipulation is to achieve complete control over the reflected wavefront without inducing unwanted spurious fields, while the aim of the tensorial metasurfaces is to realize chiral polarization control. For the scalar wavefront engineering, an optical Huygens' metasurface and a vanadium-dioxide metasurface have been devised that respectively leverage the Schelkunoff's equivalence principle and the theory of holography. A detailed analysis on an optical Huygens' metasurface is presented whereby surface losses, which have heretofore been considered merely as an undesirable feature, have been discovered to play a critical role in suppressing unwanted excitations. An investigation has also been conducted on reconfigurable scalar metasurfaces through the demonstration of a vanadium-dioxide metasurface in which the reconfigurability is attained via a large refractive index change enabled in vanadium dioxide. Instead of relying on surface losses, however, the proposed vanadium-dioxide metasurface judiciously assigns unwanted fields in the `invisible region' such that only the desired reflected fields are excited in the far-field zone. In a departure from scalar wavefront engineering, this thesis also presents optical and microwave tensorial metasurfaces for chiral polarization manipulation. For this purpose, a highly efficient optical circular polarization selective surface is demonstrated by cascading rotated silicon nanorods. The design methodology, which employs multi-conductor transmission line theory, is discussed. In the microwave regime, dual-band tensorial metasurfaces are presented. The analysis involves combining a semi-analytical method with a nonlinear optimization technique. Their physical realization is also discussed along with numerical and experimental verifications at microwaves.
Source: TSpace (University of Toronto)
Author: Min Seok Kim
Language: English
Field: Materials Science
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W3122797398