Design And Analysis Of Tunable Electromagnetic Devices In Terahertz Band

With the advantages of high penetration,low energy and wide frequency band,terahertz waves possess promising applications in communication,imaging,and medicine.However,most natural materials respond weakly to terahertz waves,which largely affects the development of terahertz technology.In this regard,metamaterials,artificially designed composite structures that exhibit electromagnetic properties beyond natural materials,offer a viable solution for the development of terahertz functional devices.However,metal-based terahertz metamaterial devices are functionally unchangeable,leading to a limited range of applications.Therefore,in this paper,three tunable electromagnetic devices are designed using the active materials vanadium dioxide and graphene combined with metamaterials,and are numerically simulated and mechanistically analyzed.The main work is as follows:1.A VO₂-based switchable device with asymmetric transmission and bidirectional narrowband absorption is designed.When VO₂ is in the insulated state,the device allows for asymmetric transmission of terahertz waves.Specifically,x-polarized and y-polarized waves incident in the forward（+z）direction are converted into the corresponding transmitted cross-polarized waves within the frequency ranges of 1.15 THz to 1.26 THz and 1.53 THz to 1.61 THz,respectively,with an asymmetric transmission coefficient greater than 0.6.On the other hand,when VO₂ is in the metallic state,the device can function as a bi-directional narrow-band absorber,achieving single-peak absorption and double-peak absorption for the forward（+z）incident x-polarized and y-polarized waves,respectively,with absorption rates exceeding 96%.Additionally,the narrow-band absorption and polarization selection characteristics of the device are used for investigating dual-peak refractive index sensing and near-field image display.2.A dual-function device based on VO₂ that can achieve both broadband reflective line polarization conversion and broadband absorption is designed.When VO₂ is in the insulated state,the device can perform broadband line polarization conversion over a relative bandwidth of 99.2%within the frequency range of 2.75THz to 8.16 THz,with a conversion efficiency greater than 90%.When VO₂ is in the metallic state,the device exhibits an absorption rate greater than 90%within the frequency range of 4.55 THz to 10.17 THz,with a relative bandwidth of 76.3%.3.A tunable absorber based on the composite metasurface of graphene and VO₂is designed.When VO₂ is in the metallic state and the chemical potential of graphene is 0 e V,the device can achieve a broadband absorption with a relative bandwidth of80.6%and an absorption rate greater than 90%in the frequency range from 1.45 THz to 3.41 THz.When VO₂ is insulated and the chemical potential of graphene is 0.7 e V,the device has an absorption rate of more than 90%in the two frequency bands of0.58 THz to 1.90 THz and 4.32 THz to 4.53 THz with relative bandwidths of 106.5%and 4.7%,respectively.Moreover,the dynamic modulation of the absorption rate can be achieved by adjusting the chemical potential of graphene.In addition,when the chemical potential of graphene is 0 e V,the device can switch the function of absorption and reflection in the frequency range of 1.45 THz to 3.41 THz by changing the phase transition of VO₂.The devices designed in this paper have potential applications in sensing,optical switching,and modulators.