Research On Characteristics Of Actively Tunable Terahertz Absorber With Amplitude And Bandwidth Based On VO₂

Metamaterial absorber is a kind of periodic artificial composite structure that can be flexibly designed to achieve nearly perfect absorption.It can produce strong electromagnetic response in the terahertz band with important applications in the fields of stealth,communication,detection,and sensing.At present,most metamaterial absorbers are fixed in their absorption performance after processing and fabrication,so that they cannot meet the multiple demands in practical applications.The resonant frequency of the metamaterial absorber is theoretically determined by the electromagnetic properties of the resonant unit,so the active material can be added to the structure to adjust its permittivity and permeability to change the electromagnetic response to the incident wave,thus reaching the purpose of modulation.The conductivity of vanadium dioxide can be changed by four or five orders of magnitude during the phase transition from the insulating dielectric state to the metallic state,with consequent changes in permittivity and magnetic permeability.There are significant differences between states of vanadium dioxide in the electromagnetic response to terahertz waves,so the design of combining vanadium dioxide with metamaterial becomes one of the research hotspots to achieve tunable absorption performance.In this paper,based on the vanadium dioxide phase transition principle,the structural design of tunable metamaterial absorbers in terahertz band is analyzed and discussed.The main contents are as follows:(1)A broadband terahertz absorbing structure with tunable absorption amplitude based on vanadium dioxide metamaterial is proposed.The simulation results show that the absorptivity of the absorber is above 90% in the frequency range of 3.01 THz-6.79 THz,i.e.,the absorption bandwidth is up 3.78 THz,which is a significant broadening of the absorption bandwidth compared with similar absorbers.By varying the conductivity of the phase change material vanadium dioxide in the range of 10 S/m-60,000 S/m,the absorptivity of the absorber varies continuously from almost zero to over 90%,indicating that active modulation of absorber absorption amplitude was achieved by controlling the conductivity of vanadium dioxide.Through the research of the absorption mechanism,it has been verified that the metallic phase vanadium dioxide has a strong electromagnetic response to incident electromagnetic waves.At the same time,the structure is centrosymmetric,so it is insensitive to polarization and the incidence angle for incident electromagnetic wave.(2)A multi-layer terahertz absorbing structure with switchable absorption bandwidth based on a thin layer of vanadium dioxide is proposed.A metal cross is used as the upper pattern layer,and a thin layer of vanadium dioxide is embedded in the dielectric layer of the structure.Based on the phase transition property of vanadium dioxide,the absorption bandwidth can be switched from narrowband to broadband.The simulation results show that when the vanadium dioxide is in the dielectric phase,the perfect absorption peak of the absorber is at 5.93 THz;when the vanadium dioxide is in the metallic phase after the phase transition,the absorptivity exceeds 90% in the frequency range of 1.97 THz-4.51 THz with an absorption bandwidth of 2.54 THz.In addition,the absorbing structure has important applications in the field of terahertz sensing when acting as a narrowband absorber,and has good polarization insensitivity and wide incidence angle when acting as a broadband absorber.