Research On Polarization Manipulation And Information Manipulation Based On Space-time-coding Metasurface

Metasurfaces are two-dimensional(2D)artificial electromagnetic(EM)surfaces composed of periodic or non-periodic sub-wavelength EM resonance structures,their unique EM wave manipulation properties play an important role in beamforming,holographic imaging,RCS reduction,multi-physical field controlling,and so on.Since the concept of programmable metasurfaces was put forward in 2014,the reflection/transmission properties of EM waves can be real-time controlled in a field-programmable way,which makes the programmable metasurfaces the universal implementation platforms for the intelligent EM wave manipulations and multi-functional EM devices.In recent years,the proposals and developments of time-domain coding metasurfaces(TDCMs)and space-time coding metasurfaces(STCMs)have further broadened the research and application scopes.Through the joint digital coding strategies in the time domain and space domain,STCMs are capable of dynamic control of the nonlinear spectrum and wavefront for EM waves,which provides a proven path to multi-harmonic beam joint manipulation,non-reciprocal EM transmission,Doppler stealth,and intelligent wireless communication.In view of the powerful nonlinear harmonic manipulation capacity of TDCMs and STCMs,this dissertation focuses on their EM wave manipulation technologies and applications at physical and information levels,including polarization manipulation,frequency-modulated continuous wave generation and manipulation,and wireless communication.The main research contents and contributions of this dissertation are summarized as follows:1.The concept of time-division multiplexed TDCM is proposed,which can realize the simultaneous reconfigurations of polarization and frequency properties of the transmitted waves.By changing the time-varying transmission properties in different polarization time slots,the general theory and implementation method are systematically summarized.For experimental verifications,a transmissive time-division multiplexed TDCM sample integrated with PIN diodes was designed and fabricated,whose transmission polarization property and phase response depend on the combination of working states of multiple PIN diodes.By providing specific time-varying control voltage signals to the PIN diodes,arbitrary linear-polarized transmitted wave reconfiguration at the fundamental frequency and dynamic polarization manipulation of the even-order nonlinear transmitted harmonic can be realized,confirming the feasibility of simultaneous reconfigurations of polarization and frequency of the transmitted waves.2.A polarization-independent phase-controllable anisotropic TDCM is proposed,which can realize the programmable polarization syntheses of the fundamental and nonlinear reflected harmonics.By conducting periodic phase pulse modulation with variable duty ratios in a single polarization direction,various polarization syntheses at the fundamental frequency can be realized.By simultaneously conducting periodic phase pulse modulations with variable time delays and initial phases in dual polarization directions,nonlinear polarization synthesis can be realized.A reflective anisotropic TDCM sample integrated with varactor diodes was designed and fabricated to experimentally validate arbitrary linear-polarized reflected wave synthesis of the fundamental frequency and nonlinear reflected harmonic polarization synthesis.The measured results are in good agreement with the theoretical predictions,which confirm the feasibility of programmable polarization synthesis methods of fundamental and nonlinear reflected harmonics.3.A method of frequency-modulated continuous wave(FMCW)generation and beamforming based on the nonlinear periodic phase-modulated STCM is proposed.By rationally constructing the nonlinear periodic phase responses of STCM,the FMCW signals with different time-frequency properties can be generated on demand.On this basis,by designing the initial phase gradients in different regions of STCM,the propagation direction of the FMCW beam can be controlled.A 360°phase-controllable reflective STCM sample was designed and fabricated for experimental validation of the FMCW generation and beamforming,thereby confirming the practicability of the proposed method.4.A space-frequency-polarization-division multiplexed wireless communication architecture based on an anisotropic STCM is proposed,which can improve the channel capacity and space utilization.Based on the polarization-division multiplexed architecture of the anisotropic STCM,the baseband signals of two polarization channels can be modulated onto different nonlinear harmonics,which realizes the frequency-polarization-division multiplexed modulation.Subsequently,by introducing different delay gradients into the control voltage sequences of two polarization directions,the harmonic beams in two polarization directions can be steered to specified directions respectively,thereby realizing the space-frequency-polarization-division multiplexed modulation.Finally,the real-time data transmission capabilities of the frequency-polarization-division multiplexed and space-frequency-polarization-division multiplexed wireless communication systems were experimentally validated respectively,which confirms the practicability of the proposed wireless communication architecture.