Research On The Design And Regulation Performance Of Polarization Regulator Based On Metamaterials

Polarization,as one of the basic spatial characteristics of electromagnetic waves,plays an important role in communication.With the diversification of appl ication scenarios,we hope to change the state of polarization and regulate polarization freely.Traditional polarization regulators are realized by using birefringent crystals or Kerr effect,which has its own limitations,such as a narrow frequency band,only working in the optical band,precise and large thickness.These shortcomings greatly limit its application.Therefore,people have been working to find a polarization converter with better performance and more relaxed conditions.Metamaterials are artificially structured materials that use micro-units for periodic arrangement,which can exhibit electromagnetic properties that are not found in natural substances.Different unit structures,materials and arrangements can achieve different functions.Thi s new material with designable electromagnetic properties provides a new idea for the design of polarization regulators.The current metamaterial-based polarization regulator is in rapid development.The existing metamaterial polarization regulators still can be inproved in many aspects.(1)Most devices can only work at small incident angles and have strong angular sensitivity.(2)The bandwidth and performance of the polarization regulator in the terahertz band still need to be further improved.To solve these two problems,two metamaterial polarization regulators are designed in this thesis.The specific research contents are as follows:(1)A circular polarization regulator based on a z-shaped chiral metamaterial is proposed,which can keep the reflected wave in the same circular polarization mode as the incident wave.The results show that the polarization conversion rate of the device is always greater than 90% in the frequency range of 8.18GHz-13.988 GHz at normal incidence.At oblique incidence,the device can still keep more than 90% polarization conversion rate in the X-band at 75°.The influence of the azimuth angle on the polarization conversion rate of the device is analyzed,and result show that the device is azimuth-insensitive.The insensitivity of the incident angle and the azimuth angle meets the current requirements for more relaxed use conditions.Through the absorption characteristics of the device,the physical mechanism of the device is discussed.The results show that the selective absorption of the device will weaken the co-polarization component in the reflected wave,thereby reducing the polarization conversion efficiency of the corresponding frequency band.Finally,by discussing the influence of model parameters on device performance,the optimization ideas of the device are given.(2)A dual-function polarization regulator based on an elliptical anisotropic metamaterial is proposed.The device is a reflective device,which can not only realize the orthogonal conversion to the linearly polarized incident wave,but also keep circular polarization mode in the reflected wave same as the incident wave.Through calculation of the polarization conversion rate,it can be found that the polarization regulate efficiency of the linearly polarized wave and the circularly polarized wave are completely same,and when the terahertz wave is incident vertically,the polarization conversion rate of the device reaches more than 90% in the band of 0.45THz-1.152 THz,and there are four resonance points.The polarization state of the reflected wave was analyzed by the coordinate decomposition method,and the orthogonal conversion function under linear polarization incidence was verified.Using formula derivation proves that the regulation efficiency of anisotropic metamaterials on circularly polarized waves is exactly the same as the linear polarization conversion efficiency,which verifies the dual-function characteristics of the device.In addition,the regulation mechanism of the device is analyzed by the surface current method,and the results show that the broadband effect of the device is due to the superposition of the fourth-order electromagnetic resonance of the device.This work enriches the theory of polarization regulators,and plays an important rol e in guiding the design of more efficient and practical polarization regulators.