Design And Fabrication Of Multi-band Negative Index Metamaterials

Negative refractive index(NRI) have given raise to the study in metamaterials intensely as a novel electromagnetic characteristics of material, and the interest in NRI are motivated because of its potential applications such as invisible cloak, superlens and imaging bellow diffraction limit. To promote NRI on practice, exploiting multiband, polarization insensitive, vertical incident and easy fabrication is the main tendency in this field. For insensibility and vertical incident, some theoretical researches have shown that the structure geometry need to be symmetric in orientation of polarization and be sandwich-shaped(metaldielectric-metal) in direction of incidence. And, designing same and simple pattern in a plane can ameliorate inconvenience of fabrication. Therefore, lots of study invade this field about increasing the response NRI channels. Notably, the NRI operating in THz is rare, especially for dual-band and more seriously for triple-band. The most general and simple methods achieving multiband NIM is to combine different magnetic resonators in same period. We focus attention on scattering parameters and corresponding retrieved optical constants from single magnetic resonator utilizing full-wave 3D finite element method(FEM) simulations package(COMSOL Multiphysics). Based on it, we extended the size, operating range, and the number of resonances and gained some desired performances.We verify the validity and accuracy by comparing the results calculated using S-parameter retrieval method with the one in reference. The FEM is expensive in memory and running time when simulating some 3D modes, so we simplify the meshing and reduce simulation space according to field distribution and symmetry of structure related to boundary condition in simulation, which improve the efficiency tremendously.It is analyzed specifically that the NRI performance dependence on geometry variations of a square ring pairs(SRPs) including negative magnetic resonance and intensity. We obtained multiband NRI located in mid-infrared spectrum with the support we got from SRPs and pushed its responses into THz regime by tailoring geometry parameters. Furthermore, we designed a new cross-ring-shaped THz resonator capable of negative permeability inspired by corresponding structure in reference and another new dual band, p olarization insensitive NRI metamaterial at THz frequency via assembling it with fishnet pairs and cross pairs.In addition, SPRs is modified to decrease metal proportion because of its strong reflection, which generates another new negative magnetic reso nator. And combining it with cross pairs and its ring version in a same periodic yield a new triple-band magnetic resonator firstly. No feasibility of NRI modulation via contact directly between metal and graphene is analyzed particularly.Finally,we exploited the photoresist thickness dependence on rotate speed and time of spin coater and gain the influence of exposure, prebake and development time on lithography patterns.