Research On THz Polarization,Absorption And Sensing Devices Based On Metamaterials

Terahertz（THz）wave has a wide application prospect in astronomy,biomedicine,atmospheric monitoring,energy,terahertz communication,radar detection and so on because of its unique characteristics.High performance terahertz functional devices are one of the main bottlenecks in the development of technology.Electromagnetic metamaterial is one kind of artificial composite electromagnetic material which is formed by periodic or aperiodic arrangement of sub-wavelength unit structures.It provides a new way to realize terahertz functional devices.In this paper,controllable and multi-band polarization converters,wideband terahertz absorbers and high sensitivity terahertz sensors for cell concentration detection based on metamaterial are designed,respectively.The main research contents and innovation points of this paper can be summarized as follows:1.A three-band terahertz polarization rotation device based on chiral metamaterial is designed,which can rotate 90 degrees for the polarization direction of the incident terahertz wave.In order to realize the"on"or"off"functions of polarization conversion,the device uses the characteristic that Vanadium dioxide（VO₂）can change from insulating state to metal state when the light field or electric field is applied.The simulation results show that the incident linear terahertz wave can be rotated 90 degrees in the polarization direction near three resonant frequencies when it is set in the"on"state.The polarization conversion rate（PCR）of the device at 0.253 THz,0.368 THz and 0.479 THz are 97.52%,89.03%and 88.90%,respectively.2.A multi-band linear polarization convertor with the shape of“tree crotches”is proposed in this paper.It can rotate 90 degrees in the polarization direction of the incident wave in multiple resonant frequencies.This linear polarization converter can achieve a linear polarization conversion rate of more than 90%in the frequency range of 1.423 THz,1.758-2.088 THz and 2.178 THz.3.A polarization-insensitive broadband terahertz absorber,which is arranged by a mixture of rhombus and circular metallic patches is proposed in this paper.Its operating frequency covers the frequency range of 0.22-0.33 THz which is corresponding to the current mature electronic terahertz radiation source based on electronic method.The absorptivity of the absorber can reach 99.93%at the frequency point of 0.3 THz,and the frequency range whose absorption rate exceeds80%is 0.132 THz.4.An anisotropic metamaterial biosensor based on Fano resonance is designed and proposed.The sensor has two Fano resonant valleys,A and B.For resonant valley A,the sensing sensitivity can reach 112 GHz/RIU,and for resonant valley B,the sensing sensitivity can reach 234 GHz/RIU.Simulation and experimental results show that the biosensor can detect cancer cells with low concentrations.For cancer cells treated with 120μmol/L anticancer drugs,the sensitivity of resonant valley A is 0.84 GHz,and the sensitivity of resonant valley B is 6.77 GHz.For cancer cells treated with 90μmol/L anticancer drugs,the sensitivity of resonant valley A is22.00 GHz,and the sensitivity of resonant valley B is 51.82 GHz.The results show that the sensing sensitivity of resonant valley B is significantly higher than that of resonant valley A with the same drug concentration,which indicates that the resonant valleys corresponding to high-order modes of the metamaterial biosensor have higher sensitivity than lower-order modes.