Research On Imaging Properties Of The Two-Dimensional Transmission-Line Metamaterial

In 1968, Veselago theoretically investigated substances with simulataneously negative permittivity and permeability, and predicted their unusual electromagnetic properties such as reverse Snell law (negative refraction), reverse Doppler effect and reverse Cerenkov radiation. Since such materials were not available in nature, the interesting concept of negative refraction, and its various electromagnetic and optical consequences, suggested by Veselago had received little attention. Until recently, Smith et al. realized the first negative-refractive-index material in the microwave ranges by constructing two dimensional arrays consisted of split-ring resonators and wires, and now the field is becoming one of the hot focuses of international electromagnetics and optics research. Conventional lenses focus electromagnetic waves by applying a phase correction to the propagating Fourier components, emanating from a source. The evanescent Fourier components which decay in amplitude away from the source, however, are lost and limit the image resolution of conventional lenses to approximately one wavelength. The flat slab of negative-refractive-index (NRI) material can correct the phase of propagating Fourier components but also restore the amplitudes of evanescent waves at the focal plane, and is capable of overcoming the conventional diffraction limit and produce an image with sub-wavelength resolution for the object.The works presented in the thesis mainly focus on the intensive researches about the impedance matching on the boundaries of the negative-refractive-index transmission-line slab lens, the tunneling effect and imaging properties of a pair of 2-D L (inductance) loaded and C (capacitance) loaded transmission-line metamaterial slabs and the imaging properties of a negative-refractive-index transmission-line slab lens excited by an embedded source. The main research activities and valuable results gained are detailed as follows:1. Method of equivalent circuit for an incremental length of transmission line is proposed to analyze both the two-dimensional LC (inductance capacitance) loaded transmission-line unit cell and unload transmission-line unit cell. The dispersion characteristics which aid in the design of such structures are derived. Simulation results of negative refraction ascertained the proposed method is valid.2. Based on the wave equation of a general two-dimensional distributed network excited by a distributed current source, the radial transmission-line impedance and voltage distribution for two-dimensional LC loaded transmission-line unit cell and unload transmission-line unit cell are systematically investigated, which can solve the problems of impedance matching for the finite negative-refractive-index transmission-line lens system. Based on the studies on the radial transmission-line impedance and voltage distribution, an approach to design an equivalent infinite slab lens system composed of negative-refractive-index transmission-line material is proposed.3. Based on the theory of plane wave propagation in stratified media, Unusual electromagnetic properties of a pair of 2-D L loaded and C loaded transmission-line metamaterial slabs are investigated in detail. Our anlysis shows that by judiciously selecting the Bloch impedances and wavenumbers in the z-direction for L loaded and C loaded transmission-line media and the thicknesses of each slab, All spatial Fourier components, including propagating and evanescent voltage waves, can tunnel through the paired L loaded and C loaded transmission-line structure, and show up the exit face with the same corresponding values (in magnitude, phase and propagating direction) as their values at the entrance face, which lead to sub-wavelength virtual imaging. This effect may conceptually provide an interesting future application in image reconstruction, resolution enhancement, and near-field subwavelength imaging.4. A novel approach for subwavelength imaging using a negative-refractive-index transmission-line slab lens excited by an embedded source is proposed for the first time. The plane voltage wave interaction with a negative-refractive-index transmission-line slab lens is analyzed. The imaging properties of the slab lens were studied. Both the microwave-circuit simulation and numerical simulation show that such a slab leads to growing evanescent voltage wave away from the source in the slab, thus the amplitudes of evanescent voltage waves at the source are exactly reconstructed at the images.