Active Regulation Mechanism Of Terahertz Waves Based On VO₂ Metasurface

The unique advantages of terahertz wave make it have great application prospects in broadband communication,airport security,substance detection,biomedicine and other fields.To realize the effective regulation of terahertz wave is the basis of the popularization and application of terahertz technology.At present,the means of regulating terahertz waves are limited,and the modulators with high modulation speed and large modulation depth are relatively scarce,which is mainly attributed to the poor response of natural materials to terahertz waves.The appearance of metasurface solves this problem,and the introduction of tunable materials into metasurface can realize the active regulation of terahertz waves.Under external excitation,the conductivity of phase change material vanadium dioxide will change by 5 orders of magnitude.By combining vanadium oxide with metasurface,terahertz regulatory devices with large modulation depth and low insertion loss can be realized.Therefore,the amplitude and phase modulator of terahertz waves is designed based on vanadium dioxide in this thesis,and the mechanism of metasurface’s active regulation of terahertz waves is studied as follows:1.A terahertz wave amplitude modulator based on VO₂ metasurface is designed and its active regulation mechanism is analyzed and verified.The continuous active regulation of terahertz wave amplitude is realized by using the phase transition characteristic of vanadium dioxide.The physical simulation model of the metasurface was established with the help of CST electromagnetic simulation software,and the parameters were optimized,and the amplitude control device with modulation depth of99.99%was obtained.The transmission amplitude spectrum of the device,the surface current distribution diagram and the electric field diagram of the resonant structure at the resonant frequency point are analyzed,and the resonant response induced by the incident wave is studied,and then the mechanism of metasurface’s active regulation of terahertz wave amplitude is obtained.This terahertz amplitude modulator based on phase change vanadium dioxide has the advantages of small volume,easy integration,large modulation depth,low insertion loss,simple process,easy processing,and so on.It has important application value in the future field of terahertz broadband communication.2.A terahertz phase modulator based on VO₂metasurface is designed and its active regulation mechanism is analyzed and verified.By using CST simulation software,the physical model is established and the parameters are optimized.Finally,the phase modulator with wide band and large phase shift is realized.The simulation results show that when vanadium dioxide changes from insulation phase to metal phase,the device phase shift is greater than 90°in the wide band of 0.84～1.05THz,and the maximum phase shift is 152.63°at 0.96THz.On this basis,a metasurface based active regulation of terahertz amplitude and phase is proposed.By comparing and analyzing the influence of different vanadium dioxide conductivity on the amplitude spectrum and phase spectrum of the transmission coefficient of the device and the surface current distribution and electric field diagram of the resonant structure at the resonant frequency point,it is found that the phase control of the device is based on the local surface plasmonic resonance principle.By introducing the phase change material vanadium dioxide,the device structure is continuously reconstructed by using its insulation-metal phase change characteristics.The resonant mode of the electric dipole of the structure is changed to realize continuous active regulation of the phase of the terahertz wave.This terahertz phase modulator based on phase transition vanadium dioxide has great potential for applications in terahertz wireless communication,security imaging,sensing and other fields.