Study On Graphene Based High Sensitivity SPR Gas Sensor In The THz Band

Terahertz waves have unique properties,especially in biomolecular detection,medical imaging,gas pollution detection.In recent years,due to excellent properties of graphene in THz band and development of surface plasmon resonance theory and technology,THz technology can achieve high sensitive sensing,zero pollution and no harm,and inject a new idea for the development of sensing field.THz sensing technology has made great development,but the present situation of the research on gas sensing is little breakthrough,according to this situation we hope to combine surface plasmon resonance technology and graphene technology to achieve high sensitivity gas sensing and make in-depth theoretical research.When the THz wave is incident on the Otto mode device by the total reflection,the evanescent wave and plasma wave of graphene surface occur resonance,resulting in a huge absorption peaks in the reflection spectrum.The slight change of refractive index of gas by plasma surface technology can be captured,and be also enlarged by deviation of resonance angle.In my thesis,a high sensitivity gas sensor based on Otto device is designed,and its working frequency can reach 3-6THz through the parameter optimization.And magnetic field was introduced to regulate the dielectric constant of graphene making the sensor sensitivity increase more than 20 times at the same time and also the sensor tenability increase.1.The theoretical analysis for the surface plasmon resonance condition shows that the dielectric constant of the material on both sides of the interface of metal and dielectric must be one positive and one negative to excite the surface plasmon resonance,and it must be the light wave of the TM mode.2.The dispersion characteristics of graphene introduced instead of metal is analyzed in detail.The results show that the dielectric constant of graphene is a function of the frequency of the electromagnetic wave and the double modulation of the applied electric field and magnetic field.The external electric field changes the dielectric constant of graphene by affecting the chemical potential of graphene,while the change of the magnetic field will directly lead to the modification of the dielectric constant of the graphene.More importantly,compared with the high loss of the metal in the terahertz band which is because the imaginary part of metal in THz band is much larger than the real part,the properties of graphene in this band are quite the opposite,providing the possibility for the development of the THz band SPR sensing technology.3.Based on the principle of attenuated total reflection,an improved Otto device is designed,which consists of four layers of high refractive index prism-organic dielectric layer-monolayer graphene-gas analyte measured.The difficulty of controling the gas gap for the original Otto device accurately is solved.The addition of graphene enables the gas sensing to be realized by the SPR sensing technology and can be operated in terahertz band making gas sensing more sensitive and safe.4.The SPR gas sensing characteristics are simulated by MATLAB software,and a high sensitivity detection scheme for gas refractive index is discussed.The effects of the thickness of the organic medium,the refractive index,the frequency of the incident light wave and the electric field and magnetic field on the performance of the sensor are analyzed in detail.The results show that the bandwidth of the sensor can reach 3-6THz,and the addition of magnetic field makes the sensitivity increase by 20 times.