Study On Terahertz Gas Sensing Technology Of Metal Array Local Surface Plasmon

Terahertz sub-wavelength metal structure devices,due to their special size and structure,have unique optical properties.They are usually used in the research fields of abnormal transmission,breakthrough of diffraction limit,sensing and so on.In this thesis,combined the theory of terahertz local surface plasmon resonance with COMSOL Multiphysics simulation software,the metal array gas sensor is simulated.And the effects of the shape and the size of the metal array on the parameters of terahertz transmission and refractive index sensitivity are studied.The main findings and innovations are as follows:1.The application of terahertz gas sensing is realized by designing sub-wavelength metal array structure sensor to generate terahertz local surface plasmon.In general,surface plasmon is produced in the visible and near infrared bands,while in the terahertz band the plasmon loses their optical field limiting power and can hardly be produced.The terahertz surface plasmon resonance can be generated by coupling the metal array,grating and other structures with the surface plasmon.In terahertz band,surface plasmon confined to certain metal structures are called terahertz local surface plasmon.2.By using COMSOL Multiphysics software,and based on the Drude model,the theoretical models of metal array structure sensor with triangular,cylindrical and square column are established.Based on the finite element method,the refractive index sensing characteristics of the sensor are simulated and designed by optimizing the modeling process,boundary conditions,excitation source,and mesh division and so on.3.The sensing characteristics of local surface plasmon triangular column metal array structure are studied in detail.The parameters of the triangular column metal array structure are set as follows: the triangular column has a square triangle side length of a = 80 ?m,a height of h = 5 ?m,and the array period is T = 200 ?m.The transmittance of the terahertz wave at 1 ~ 3 THz and the refractive index sensitivity of the metal array structure sensor are studied.The results show that the frequency of the transmission valley decreases with the increase of the refractive index of the gas,and the refractive index sensitivity is 1.29 THz / RIU.When the side length of the triangle is a = 60 ?m,the height is h = 5 ?m,the array period is T = 200 ?m,and the refractive index sensitivity is 1.40 THz / RIU,1.19 THz / RIU,respectively.It can also be seen that the refractive index sensitivity decreases gradually when the side length of the triangle becomes larger.However,when the side length of the triangle is invariant,the refractive index sensitivity is not sensitive to the variation of period T or height h.4.The effects of structural parameters of cylindrical and square cylindrical metal array structure sensors on their sensing characteristics are also studied.The circular radius of the cylinder is r = 22.3 ?m,29.7 ?m,37.1 ?m,the height is h = 5 ?m,the array period is T = 200 ?m,the refractive index sensitivity is 0.54 THz / RIU,0.52 THz / RIU,0.50 THz / RIU,respectively.The side length of the square column is b = 39.5 ?m,52.6 ?m,65.8 ?m,the height is h = 5 ?m,the array period is T = 200 ?m,and the refractive index sensitivity is 1.03 THz / RIU,0.91 THz / RIU,0.59 THz / RIU,respectively.Through the analysis of the THz transmittance spectrum of the sensor and the sensing parameters,it can be found that for the triangular column,the cylinder,the square column metal array structure,the transmittance valley value decreases with the increase of the refractive index of the gas.But the transmittance of columns and square columns vary less than triangular columns.The refractive index sensitivity decreases gradually with the increase of geometric size.And the refractive index sensitivity and its change of triangle column is the highest,and the cylinder is the least.In a word,this thesis combines the local surface plasmon resonance theoretically with the sub-wavelength metal array structure in the design of the device,extending from visible light and near infrared band to terahertz band,extending from the range of 0.1 ~ 1 THz and 3 ~ 10 THz to 1 ~ 3 THz.And the influence of the size and shape of metal structures corresponding its sensing characteristics is also analyzed.When the geometry of metal array is given,the sensitivity of refractive index decreases with the increase of geometric size.The refractive index sensitivity of triangle column is the highest and the change is also when the geometry size is fixed,the second is square column,and the cylinder is the least.It can be obtained that the sharp angle structure can enhance the refractive index sensitivity of the metal array structure sensor.This research provides an effective reference for the design of terahertz sensing devices based on the local surface plasmon resonance,and also has certain application value in the areas of biochemical medicine,gas monitoring and so on.