Experimental and theoretical studies of left-handed metamaterials

Abstract

Three decades after V. Veselago predicted wave propagation for simultaneously negative permittivity (ε) and permeability (μ), Sir J.B. Pendry proposed structured materials to realize Veselago’s prediction. These metamaterials theoretically studied and experimentally demonstrated first at microwave frequencies, soon became a topic of extensive research. With exciting visions of prospective applications such as a perfect lens with subwavelength resolution, or miniature electromagnetic devices, one of the propelling forces in metamaterial research has been pushing the operating frequencies higher with the ultimate goal of realizing metamaterials for photonics. In this thesis, after presenting a theoretical background of left-handed metamaterials, artificial building blocks such as the split-ring resonators (SRRs), continuous wires, and slab-pairs and their general response is discussed. Next, composite metamaterials consisting of SRRs and continuous wires operating at microwave frequencies are presented. At the same time, the term left-handed behaviour and the criteria that determine this behaviour are discussed in detail with specific examples of composite metamaterials operating at microwave frequencies. Studies regarding a comparison of in-plane and off-plane SRR-wire placement, and electrical excitation of magnetic resonance (EEMR) effect are included. Finally, the effect of SRRs on electric (not magnetic) resonance of the composite structure is investigated and it was found that this effect has significant consequences regarding the design for LH behaviour. Furthermore, numerical studies of left-handed materials based on the split ring resonator (SRR) element are presented. The effect of the geometry of the SRR on its negative permeability response is investigated extensively. In addition, a detailed study of the dependence of the LH transmission on various other geometrical and material parameters of the system is examined. Next, the composite metamaterials operating in the far infrared frequency region are investigated. Different designs operating at THz frequencies are presented. First, the SRR and multi-gap SRR designs are introduced. The microfabrication process for the fabrication of those designs and the transmission and reflection measurements performed by using Fourier transform infrared spectroscopy (FTIR) are discussed in detail. Then, the slab pair- continuous wire design is presented and the FTIR measurements of these samples are presented and discussed. Finally, we present our studies on switchable SRR structures created by incorporating proper photoconductive material in ordinary SRRs. We study various configurations of the photoconductive material and their effects on the switching properties of the SRRs by simulating the effect of conductivity variation. Three different configurations that are applicable under certain fabrication and/or optical excitation conditions are described and investigated.