Study Of The Chiral Metamaterial On Electromagnetic Polarization Transformer

Electronic metamaterials are a kind of a composite material, which is composed of artificial design structure, and presents superior physical properties that the natural material does not have. The metamaterials present a wide application prospect in the field of electromagnetic polarization transformer. Based on the characteristics of the chiral structure, the chiral metamaterials have the properties of optical activity, circular dichroism, topology of light insulation and so on. This thesis presents a study of the application of chiral metamaterial polarization transformer, which is on the basis of the basic theory of chiral metamaterials polarization transformer. The thesis also studies the characteristics of 90° polarization rotator and circular polarization devices using the chiral metamaterials based on theoretical analysis, simulation and experimental measurement. The main contents of this thesis are as follows:1) A kind of chiral metamaterial 90° polarization rotator based on the 4-V structure is designed, this structure is asymmetry in up and down layer. Simulation and formula computing indicate that this chiral metamaterial achieves the 90° and-87.51° polarization rotation in the frequency of 15.63 GHz and 19.1GHz, respectively. The asymmetry in up and down layer in chiral metamaterial provides a new idea for the following study.2) A dual band chiral metamaterial of 90° polarization rotator based on e-shaped is designed. This 90° polarization rotator is based on the C4 unit cell structure, the geometrical shape of the structure is similar to the English letter e. Simulation presents that, in the frequency of 7.84 GHz and 8.43 GHz, the PCR is nearly 100%, the transmission efficiency is above 96.5%, the ellipticitiy angles are nearly 0° and the polarization rotation angles are nearly 90°. Based on the polarization transformer theory, this structure can realize 90° polarization rotation in two resonant points.3) A 4-I unit cell of 90° polarization rotator using chiral metamaterial is proposed. Which consists a bilayered chiral metamaterial composed of capacity-loaded fourfold symmetry(C4 symmetry) structure. Due to the C4 symmetry, the polarization mode and angel of incident wave have the property of insensitivity. The results of simulation and measurement indicate that the capacity-loaded structure can strengthen the optical activity. In addition, this chiral metamaterial has very low loss and very high polarization conversion ratio(PCR, about 99.6%), the transmission efficiency reaches 98%. The polarization rotation angles are nearly 90° and the ellipticitiy angles are nearly 0° in two resonant points, respectively.4) A chiral metamaterial of broadband circular polarization device composed of two split-ring resonators and a patch is proposed. This thesis studies the electromagnetic characteristics by the means of simulation, while the incident wave are vertical incidence and oblique incidence. When the incident wave is vertical incidence, the circular polarization device presents giant chirality and circular dichroism, and the bandwidth of this structure is more than 1Ghz, when the gain of this structure is lower than-10 dB around the resonant point. When the incident wave is oblique incidence, the chiral metamaterial has capacity of circular polarization rotation in wide angle of incidence(from 0° to 40°), which is a wide angle circular polarization device.