Research On Key Technologies Of Digital Reconfigurable Electromagnetic Metasurface

In recent years,terahertz technology is becoming a research hotspot.From the perspective of electromagnetic spectrum division,terahertz is in the middle band of the transition from millimeter wave frequency band to infrared frequency band,which has the characteristics of both electronic science and photonic science.It can effectively solve the problem of scarce spectrum resources in millimeter wave frequency band,and will play an important role in UWB wireless communication and other fields.However,terahertz device designed based on traditional electromagnetic theory usually has a high profile,high loss and the high cost of shortcomings,which greatly limits the further development of terahertz technology.Fortunately,as a new type of artificial electromagnetic structure,electromagnetic metasurface can not only realize low profile of devices,but also effectively regulate the phase,amplitude and polarization of electromagnetic waves.At present,metasurface devices with different functions are widely used in the terahertz frequency band,but they also bring problems such as single working frequency band and narrow working bandwidth.Therefore,this thesis focuses on the terahertz frequency band and designs digital metasurfaces with reconfigurable radiation pattern and reconfigurable frequencies based on the phase principle of pancharanam-berry(PB)by utilizing the tunable properties of the adjustable materials(graphene and vanadium dioxide).The main research contents are summarized as follows:1)Based on the PB phase principle,the graphene unit works in the 1.84-2.12 THz frequency band through voltage regulation of Fermi energy level,and the concept of convolution in signal system is applied to the design of metasurface.Taking the 3-bit graphene unit as an example,a series of reflective digital metasurfaces with different coding sequences were designed to flexibly manipulate the wavefront of the incident electromagnetic wave,which can realize the functions of beam splitting and vortex beam generation.And it verify the effect of the coding sequences on the deflection of the far-field direction,which provide a basis for beam scanning in the upper half of space with a finite number of units.2)A series of reconfigurable metasurfaces with different coding sequences work on the terahertz frequency band are designed by utilizing the electromagnetic characteristics of vanadium dioxide material whose conductivity changes with temperature.Generally speaking,vanadium dioxide is in an insulating state at room temperature;as the temperature gradually rises,vanadium dioxide will gradually become metallic,and its conductivity will change from 10S/mto 105S/min the process.In our research,the temperature was set at 298K and 358K,respectively,and the corresponding operating frequency band of the unit was reduced from 3.76-3.84 THz to 1.18-1.47 THz.This unit was used to design a digital metasurface,which verified the applicability of the generalized Snell law in the terahertz frequency band.