Design And Research Of Functional Devices Based On Layered Metasurfaces

Electromagnetic metasurface is an artificially designed composite structure.The electromagnetic properties exhibited by them,such as negative refractive index,negative permittivity,and negative permeability,which are difficult to achieve by natural materials,are important for regulating electromagnetic waves.Parameters such as amplitude,phase and polarization offer unprecedented possibilities.This paper focuses on the flexible regulation of electromagnetic waves by metasurfaces.Based on the analysis of electromagnetic theory,reflection type linear-to-circular/linear-to-cross linear polarization converters,transmission linear-to-circular polarization converters,and dynamic metasurface functional devices are designed.Numerical simulations verify their electromagnetic parameters and study their electromagnetic properties.The main work of this thesis is as follows:(1)Aiming at different application scenarios of electromagnetic wave polarization,a dual-function polarization converter is proposed.The polarization converter unit consists of a double split ring structure etched on a dielectric plate.The coupling effect between the double-split ring structures can effectively expand its working bandwidth.The finite integral method is used to analyze the polarization characteristics.The simulation results show it can realize LTC polarization conversion over the frequency band from 5.5-8.55 GHz,and its energy conversion efficiency is better than 99.5%.Moreover,LTL polarization conversion is also achieved in another frequency band from 10.31-15.31 GHz,and its polarization conversion ratio is greater than 0.99.In the experiment,a sample was prepared and its polarization conversion characteristics were tested.The experimental results are in accordance with the simulation results,verifying effectiveness of the converter design.(2)Aiming at the demand for broadband circular polarization in wireless communication,a broadband wide-angle line-to-circular polarization converter based on three-layer stripline metasurface is proposed.The polarization converter unit consists of three stripline metal layers separated by two dielectric plates.The different electromagnetic response characteristics of the unit in two orthogonal directions can make the amplitudes of the two orthogonal components of the transmitted wave equal and the phase difference be 90° to achieve the purpose of circular polarization.To better understand the working principle of the proposed converter,a detailed equivalent circuit model is presented for quantitative analysis.The simulation results indicate that the converter can convert linearly polarized incident waves into circularly polarized transmitted waves in the frequency range of 4.96–12.44 GHz.For an increased incident angle of 50°,the device can still maintain an axial ratio bandwidth of 53.7% in the x-z and y-z planes.(3)Aiming at the multifunctional application of metasurfaces,a tunable metasurface functional device integrating absorption,reflection and transmission is proposed.By independently controlling the physical properties(insulator or metal)of different layers of vanadium dioxide,the device realizes the integration of electromagnetic wave regulation of absorption,reflection,and transmission,and can obtain at least four working states,which are wave absorbing("11"),reflection type linear-circular polarization conversion("01"),transmissive like-electromagnetically induced transparency("10"),transmissive like-electromagnetically induced transparency and linear-circular polarization conversion("00").