| The special spectrum location and unique properties of terahertz wave(THz)determine its broad application in the fields of communication,medicals and security inspection.Although the rapid development of THz source and detection technology open the door for research in THz field,the lack of corresponding functional devices in this band limits the further utilization of THz waves.For this reason,this paper develops functional devices to realize two main applications in THz band based on THz metasurfaces.On one hand,the dynamic tunable THz coding metasurface is designed by combining graphene with coding metasurface.On the other hand,different metasurface biosensors operating in THz frequencies are fabricated to realize the sensitive detection of cancer cells due to the strong enhancement effect of local electric field in metasurfaces induced by THz beams.The main works of this thesis are summarized as the following:1.Graphene,the novel two-dimensional material,is integrated with coding metasurfaces to realize the dynamic modulation of THz waves.The graphene was designed into ribbon structures to integrate with metallic resonators.By designing different metal sizes and modulating E_f,the structure shows larger than 290~o of smooth phase modulation in the higher frequency of THz waves.Based on the phase profile design,a reflection-type focusing metasurface and 1-bit dynamically tunable coding metasurfaces were both demonstrated.Moreover,the degree of freedom for designing 2-bit coding metasurfaces was enhanced and the process of THz beam manipulation was also qualitatively interpreted by the convolution principle.2.All dielectric coding metasurface with the sequence of 010101…\010101 is prepared by etching method.graphene layer is transferred on non-etched surface on which the gate voltage is applied.The far-field scattering properties measured in experiments indicate that the applied gate voltage partly realizing tunable intensity of THz beams by gating voltage on coding metasurface.Especially,under the frequency of 0.7 THz,the beam at about 20~o with respect to normalized direction disappears after the applied voltage reaches 35 V,which further proves the effective switching function under the voltage at this frequency.This investigation also supplies an idea for the design of THz switcher based on transmission-type metasurfaces.3.We designed THz metasurfaces with electric resonant characteristics to realize sensitive detection of cancer cells.The electric field of non-bianisotropic resonance exhibited at 0.85 THz reaches up to 10~6 V/m,which is sensitive to the change of dielectric surroundings.The frequency shift?f would decrease under the effect of drug concentration changing from 1 to 15?M and drug action time from 24to 72 hours,implying the HSC3 cancer cells were effectively killed.The results measured by biological CCK-8 kits method agree with the trend of?f measured by proposed MMs-based biosensors.It demonstrates the feasibility of our proposed MMs-based biosensors,and may supply a valuable complementary reference for biological study.4.Moreover,the anisotropic resonant metasurfaces based on mirror-asymmetric design of plasmonic SRRs also can be used for the concentration determination of liver cancer cell Hep G2 and lung cancer cell A549.The dependences of?f and the fitted phase slope FPS on the cancer cell concentration at different polarizations indicate that the lung cancer cell A549 and liver cancer cell Hep G2 can be distinguished and determined simply based on the enclosed shapes in the radar maps without any antibody introduction.The minimum concentration of identification reduces to as low as 1×10~4 cells/m L and such identification can be kept valid in a wide range of cell concentration,ranging from 10~4 to 10~5.5.A depletion layer played by aqueous organic liquids flowing in a platform of microfluidic integrated metasurfaces,as multifunctional devices,are experimentally used to actively modulate THz waves and in-situ detect water content.The parallel coupling of the damping effect induced by a depletion layer with the resonant response by metasurfaces leads to an excellent modulation depth approaching 90%in intensity and a great difference over 210°in phase shift.In addition,Joint time-frequency analysis performed by the continuous wavelet transforms reveals the consumed energy with varying water content.The device can also be used as a sensor platform to detect residual water content in various chemical solutions.In the determination of the trace water content of the IPA solution,the detection limit approaches 6%.This feature largely promotes the function of microfluidic integrated metasurfaces platform in biosensing fields,and provides an idea for the preparation of lab-on-a-chip in future biosensor detection. |
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