Electrimagnetic Simulation And Structural Design Of Left-Handed Materials

Left-handed materials (LHM) are artificial electromagnetic materials withnegative permittivity and permeability. The electromagnetic waves propagation inleft-handed materials is investigated with finite difference time domain method.Dealing with the design of left-handed materials, a new method for designing a newtype of left-handed material is proposed, and the fractal structure, broadband,multi-band left-handed materials are studied. The main works are as follows:Firstly, ADE-FDTD method based on CPML absorbing boundary is theoreticallyderived. CPML gets good absorption effect on highly evanescent wave, late-timereflection and low-frequency interaction, and can significantly reduce memoryrequirements. Because left-handed materials are strong dispersive, the method withCPML absorbing boundary condition has a good absorption, and ADE-FDTD methodto simulate the dispersion medium with high accuracy. The isotropic and anisotropicleft-handed materials are analysed with numerical simulation."Perfect lens" andself-focusing phenomenon are presented.Secondly, with detail numerical studies of the transmission properties, thedendritic fractal left-handed materials are analyzed in this work. We investigate thedependences of the system on the thickness of the substrate, the lattice constant, andthe geometry of each branch. Through changing the parameter of the dendrite structure,we can change the resonant frequency. Especially, it is noticeable that the resonantfrequency of LH peak decreases with the increase of the geometry of each branch. Thecombination of the dendrite and line can broaden the bandwidth. Furthermore, thecomposition has a high figure of merit. Dendritic left-handed materials are used for thetransmission of electromagnetic induction in the ABA structure, verifying the tunnelingeffect in the THz frequencies. Due to the symmetry of dendritic structure, thetransmission characteristics of this ABA structure are independent of the polarizationof electromagnetic waves.Thirdly, by retrieving the constitutive effective parameters of bifilar spiralstructure, it is proved that its permittivity and permeability are negative at differentfrequencies. With the electromagnetic waves incidence either perpendicular or parallelto the surface of bifilar spiral structure, it is found that the causes of negativepermittivity are same. Previously, the investigation of single-sided left-handedmaterials was limited to microwave band. Through modifying bifilar spiralmetamaterials, we design a new single-sided left-handed material in the terahertz regime, and the design principle is explained with LC equivalent circuit. Left-handedmaterials generally consist of electric and magnetic resonators etched on each side ofthe dielectric substrate, respectively. Compared with these composite structures, thenew single-sided left-handed material has the advantage of low loss, simple structureand easy operating.Finally, single-sided left-handed materials are not only for the terahertz band, butalso for the microwave band. Different shapes of the structures are designed withchanging the single-sided left-handed materials. The diversity of single-sidedleft-handed materials is achieved. Narrow-band is an important constraining factor inthe development of left-handed materials. How to broaden the bandwidth is a problem.Based on electromagnetic theory and circuit theory, and combining LC equivalentcircuit theory, the factors affecting the bandwidth left-handed materials aretheoretically analyzed. Reasonable regulation of equivalent capacitance and equivalentinductance can improve the relative bandwidth of left-handed materials and thuselectromagnetic simulations verify the theoretical derivation. The single left-handedmaterials with different structural parameters have different resonant frequencies. Thecomposite structures of different unit cells can constitute multi-band left-handedmaterials.