| Terahertz(THz)waves are genarally in the frequency range of 0.1 to 10 THz.Due to the characteristics of spectral resolution,good perspective and security,THz technology has important application prospects in the field of materials detection,quality and quantity analyse of materials,and biomedical imaging.However,most of natural materials have no electromagnetic response in THz region,resulting in a lack of THz materials and devices.The development of THz functional devices will greatly promote the development and practical application of THz technology.Metamaterials(MMs),as a kind of electromagnetic material with controllable properties,can be designed artificially,providing an effective method for developing THz functional devices.In this thesis,we carry out research work concerning the mechanism and characteristics of THz MM functional devices;and various THz MM functional devices were proposed.The main work are summarized and listed as follows:1.A multiband THz MM absorber with three absorption peaks was proposed,with all absorption intensity more than 85%.The proposed structure has the feature of polarization independent.Furthermore,a multiband THz MM filter was proposed,and all pass bands have the fearture of low average insertion loss,steep skirts,high out-of-band rejection and polarization independent.2.A planar THz MM structure with electromagnetically induced transparency(EIT)effect was proposed,and the unit cell of the proposed structure consists of two split ring resonantors(SRRs).Due to the destructive interference between these two SRRs,the proposed structure generates a transparent window,which is a typical EIT-like effect.In addititon,a graphene-based THz MM structure composed of multilayer graphene/dielectric stacking configuration was proposed.The proposed structure has the multiple EIT-like effects,which solves the problem of polarization dependent of conventional EIT-like MMs structure.By changing the Fermi level of graphene,the transparent windows can be controlled actively,which can be applied to THz filters,optical switches.3.A planar THz MM which consists of square SRR was proposed,and the excitation of toroidal dipolar resonance is demonstrated,which has high quality factor at resonant frequency.We investigated the interaction between graphene and toroidal dipolar resonance at first time.By varying its Fermi level,the simulations show that graphene can actively modulate the transmission amplitude of toroidal dipolar resonance and the modulation depth could achieve 63.2%.Furthermore,the ultrasensitive sensing characteristic of the proposed structure has also investigated,which can be utilized for other two-dimensional materials.The proposed structure has a guiding role for the development of active THz MM devices.4.A passive THz MM sensor was proposed.Due to the excitation of the spoof surface plasmon,the proposed structure generates a very sharp resonance response in the transmission spectrum,with a very high quality factor.Meantime,the proposed structure has ultra-high film thickness sensing characteristics,and when the film thickness is less than 4 mm,its thickness sensitivity can reach 52.5 GHz/mm.In addition,we proposed a three-dimensional(3D)graphene THz MM sensor.Due to the excitation of multiple plasmon resonance modes,the proposed structure was first applied to THz sensing.By controlling the Fermi level of graphene,the resonance frequency of the proposed structure can be controlled and the active sesing can be realized.This structure provides a new method for THz sensing using graphene or other two-dimensional materials.5.A femtosecond laser micromachining experimental system was designed and constructed.We designed and processed THz MM filters which consists of periodic square rings and circular holes arrays.THz-TDS system was used to test samples,and the experimental results are consistent with the simulation results,indicating that femtosecond laser processing can be used to fabricate THz MM devices. |
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