| As new industrial technology in the 21st century,terahertz technology has broad application prospects in the fields of high-speed communications,biochemical sensing,and security inspection.Due to the electromagnetic characteristics of terahertz single pulses such as broadband,low energy,and biomacromolecule fingerprints,the research on terahertz functional devices have attracted the attention of experts and scholars.However,the inherent properties of natural materials have great limitations,making their interaction with terahertz waves weak,and it is difficult to satisfy effective modulation of terahertz waves,and it is not easy to produce a strong resonance response with terahertz waves.Therefore,the research and development of terahertz technology still face huge challenges.In recent years,two-dimensional planar metamaterials,namely metasurfaces,have unique electromagnetic properties that natural materials do not possess,and have shown great application prospects in the fields of terahertz modulation and biosensing.However,in the above-mentioned application fields,on the one hand,due to the large loss of the metasurface terahertz modulator based on the sub-wavelength structure and the difficulty of achieving ultra-sensitive dynamic modulation,the ultra-sensitive and low-loss dynamic terahertz modulator has become a topic that needs in-depth research;On the other hand,in terahertz wave sensing applications,although the resonance absorption spectrum of terahertz waves and biological macromolecules can be directly used for biosensing,the sensitivity of this method is very low,and there is a problem that it is difficult to realize ultra-sensitive biosensing.In addition,because the wavelength of terahertz waves is much larger than that of small biological molecules,it is difficult to resonate absorption.Therefore,there are problems that need to be solved directly in the detection of small biological molecules.In short,how to improve the sensitivity and detection range of terahertz biosensors is also a topic that urgently needs in-depth research.In order to explore terahertz metasurface functional devices with excellent performance,this thesis uses terahertz time-domain spectroscopy techniques and takes metasurfaces as the object,combined with emerging optoelectronic materials(graphene and perovskite)to study low-loss,ultra-sensitive dynamics terahertz modulator and ultra-sensitive biosensor.The main contents are as follows:1.Research on metasurface-based terahertz modulators(1)Designed,proposed,and prepared a modulator based on high-resistance silicon all-dielectric coding metasurface,which can modulate the 900GHz bandwidth terahertz wave far-field scattering,realizing ultra-wideband low-loss modulation,and different coding sequences can achieve different modulation effects.(2)Through the combination of graphene and metasurfaces with different subwavelength structures,three different types of metasurface terahertz modulators have been studied.Firstly,through the combination of graphene and high-resistance silicon,a Fano resonant metasurface modulator was designed.The device exhibits excellent slow light effects.Its maximum group delay is 9.73 ps and the group delay corresponding to free space propagation is 2.92 mm.In addition,the Gauss Amp model is modified to be used as the governing equation of the group delay.The correlation coefficient is as high as 0.99998,which shows that the revised Gauss Amp model can effectively describe the trend of group delay.The Fano resonant metasurface modulator provides a reference for low-loss slow light modulation.Secondly,a graphene bridged bus topology metasurface modulator is proposed.The device has excellent terahertz wave modulation performance,its resonant frequency blue shift is up to 1075 GHz and the modulation sensitivity is up to 1027 GHz/FLU.In addition,the parabola,Exp Dec1,and Asymptoticl models are used to evaluate the modulation trend of the resonance frequency.The device can also achieve dynamic stealth within a 500 GHz bandwidth and has potential application value in the field of terahertz ultra-sensitive dynamic modulation and stealth.Fanally,a modulator based on graphene metasurface is proposed and prepared,which can realize the modulation behavior of high-order Fano resonance at the Dirac point.As the Fermi level passes through the Dirac point and moves between the valence band and the conduction band,the high-order Fano resonance exhibits an abnormal optical phenomenon that disappears,appears,and disappears again.When the bias voltage changes by 0.05 V or the laser power density is changed by 7.5 m W/cm~2,the terahertz response modulation depth can reach 90%,opening a way for the design of ultra-sensitive terahertz metaphotonic devices.(3)A new type of graphene perovskite composite metasurface modulator was designed and prepared.The device has excellent terahertz response modulation performance,its amplitude modulation depth can reach 200%,the total resonancefrequ-ency shift is 800 GHz,and the modulation of the maximum phase reaches 346°.This device provides a new idea for the development of ultra-sensitive and super-surface optical devices combined with dual optoelectronic materials.2.Research on terahertz biosensors based on metasurfaces(1).Lung cancer cells and oral epithelial cells were cultured on the metasurface,and the sensitivity of three different types of electromagnetic resonance metasurface biosen sors was studied.Firstly,designed,proposed,and prepared electromagnetic induction-like transparent metasurface biosensor.The theoretical sensitivity of the biosensor based on the electromagnetically induced transparent metasurface is as high as 248.8 GHz/RIU.The A549 cancer cells are cultured on the device as an analyte.When the cell concentration increases from 0.5×10~5 cells/m L to 5×10~5 cells/m L,the shift increases from 20 GHz to 96 GHz.Secondly,a Fano resonance metasurface biosensor is designed,proposed,and prepared.The device is applied to the sensing of normal epithelial cells.The minimum detection concentration is about 2×10~4 cells/m L,and the corresponding frequency shift is 25 GHz.Fanally,designed,proposed,and prepared a multi-resonance mode integrated biosensor,which can visually detect the concentration of lung cancer cells by using the frequency shifts of different resonance modes to form a radar chart.At the same time,an abnormal electromagnetic response with frequency shift was observed.That is,as the cell concentration increases,the frequency shift of the resonance valley undergoes an increased frequency shift phase,a reduced frequency shift phase,and a re-increased frequency shift phase.By introducing a new dielectric constant?f,the perturbation theory is revised to explain the cause of abnormal frequency shift.As the order of the resonance mode increases,?f increases from-2.78 to 0.75,which means that the negative dielectric constant?f leads to abnormal frequency shifts,which enriches the idea of the biological cell detection.(2)Designed,proposed,and prepared an integrated metasurface biosensor based on patterned graphene perovskite for the qualitative detection of sericin.In theory,sericin can make graphene n-doped and drive the Fermi level from the valence band to the Dirac point,resulting in a sharp drop in conductivity.Correspondingly,the dielectric environment of the metasurface changes significantly.The sericin was successfully detected by this sensor,and its detection limit was 780 pg/m L,realizing ultra-sensitive detection. |
PDF Full Text Request