Enabling electromagnetic applications of negative-refractive-index transmission-line metamaterials part I

摘要

Metamaterials are artificial periodic media with unusual electromagnetic properties. The size of their unit cells is much smaller than the incident wavelength, thus allowing one to define effective media parameters such a permittivity ε, a permeability μ, and a refractive index n. In this work, “left-handed” metamaterials are considered for which their permittivity and permeability are both negative. These metamaterials exhibit backward-wave propagation characteristics and therefore a negative index of refraction as was predicted in the visionary work of Victor Veselago [1]. Such “left-handed” or “Negative-Refractive-Index” (NRI) media were first implemented using bulk periodic arrays of thin wires to synthesize negative permittivity and split-ring resonators to synthesize a negative permeability [2]. However, the NRI medium presented in [2] relies on resonant elements to synthesize the negative permeability thus leading to narrow bandwidths and high transmission losses. More recently, a completely planar approach for synthesizing NRI media without resonant elements was proposed in [3],[4]. The 2-Dimensional (2-D) NRI structure presented in [3],[4] was realized by periodically loading a planar network of printed transmission lines (TL) with series capacitors and shunt inductors in a dual-TL (high-pass) configuration. The 2-D NRI medium was subsequently interfaced with a commensurate conventional dielectric, leading to the first experimental demonstration of focusing from a NRI metamaterial [4], [5]. More recently, a 3-region lens arrangement was used to observe focusing beyond the diffraction limit [6]-[7] as was predicted by J.B. Pendry [9]. A similar TL approach was followed by Itoh and Caloz and led to interesting structures and circuits [10], [11]. Moreover, intriguing and useful anisotropic transmission-line metamaterials have been reported by Balmain et al. in [12]. In addition, some of the first FDTD simulations of NRI media have been reported in the pioneering work of R. Ziolkowski et al. in [13]. Further developments in the general area of Metamaterials can be found in two recent special issues: The October 2003 issue of the IEEE Transactions on Antennas and Propagation (Guest Editors R. Ziolkowski and N. Engheta) and the April 2003 issue of Optics Express (vol. 11, No. 7, Guest Editor J.B. Pendry).