Studying Electromagnetic Dynamic Characteristics Of DNG Materials

Double-Negative Material is a kind of artificial composite medium in which both the permittivity and the permeability possess negative real values at certain frequencies. In such a medium, the direction of the Poynting vector monochromatic plane wave is antiparallel to that of its phase velocity. Because of that, DNG displays some unusual electromagnetic properties such as backward-wave effect, negative refractive effect, perfect lens and a limit situation, zero index of refraction materials. Because of such novel characteristics which are different from classic mediums, the development of DNGs impressively entered the world's top ten scientific advances selected by the Science Magazine in 2003, and attracted global attention.In this dissertation, the development history of DNG and its potential applications are reviewed. Two methods to produce DNG are introduced. They are arranging periodic arrays of small metallic wires and split-ring resonators and Photonic Crystals. The finite-difference time-domain method as one of the ways to solve the electromagnetic fields is mentioned. FDTD is one of the most powerful numerical methods for the modeling of the electromagnetic wave propagation and scattering. It is based on the discretization of partial-differential wave equations. The partial-differential equations are transformed to finite-difference equations by the discretization in the time and the space. Consequently, the relation of field components and time in the discret points is obtained in the process of wave propagation.For simulating the DNGs, Drude model is introduced to build the ADEs(auxiliary differential equations). One dimensional and two dimensional simultaneous equations are established by ADEs and Maxwell equations. The stability and the convergence of the algorithm are also proved by Fourier transforming method. The time interval and space interval of the differential equations can be determined by analysis of stabilization and the theory of numerical dispersion. The area of calculation is built and the Mur absorbing boundary condition is applied at the boundary of calculational area in order to economize the resource of computer greatly. Based on the differential equations and calculational area, the electromagnetic properties of DNGs are simulated in one- and two-dimensional space. In 1D simulation, the characteristics of DNGs, backward-wave and no phase changing when continuous wave (CW) propagate in metamaterial having a zero index of refraction are simulated. When 2D simulations are made, the interactions of CW Gaussian beams with double negative metamaterials(DNG) are considered. Sub-wavelength focusing of a diverging, normally incident Gaussian beam with a planar DNG slab is demonstrated. The negative angle of refraction behavior associated with the negative index of refraction exhibited by DNG metamaterials is demonstrated. When point source is set, the results of simulation show that "perfect lens" focus beyond the Rayleigh diffraction limit. Finally, square structure model of two-dimensional periodic DNGs is developed. Based on the difference equations, programs are developed to calculate the reflection coefficient when EM wave propagates in periodic material built with DNGs cylinders. The results display that periodic structure has high refraction index at certain frequency. But when EM wave has very high frequency, coefficients of refraction approach to zero. Comparing the results of simulating and the analysis outcomes, it is showed that the difference equations can be simulated correctly.