基于流体模型的碳纳米管电离式传感器的结构优化方法

Structure optimization of carbon nanotube ionization sensor based on fluid model

与常规电离式传感器相比,碳纳米管三电极电离式气体传感器具有体积小、工作电压低的优势,对智能电网、泛在物联网的发展具有重要作用,但存在输出电流低、灵敏度低的缺点,需要从结构上对其进行优化.本文基于汤生放电原理,采用COMSOL Multiphysics多物理场直接耦合分析软件,建立了传感器二维等离子体放电流体仿真模型.研究得到了8种不同结构的传感器,在氮气背景中的静电场分布及传感器收集极平均电流密度.通过对比不同结构参数下的电场强度及电流密度值,得到了最优传感器结构.结合仿真结果,制备了8种优化结构的传感器进行实验验证,最优传感器结构具有最高的收集电流密度,与仿真结果一致,证明了本文提出的结构优化方法的可行性.基于最优结构,制作了100和120μm极间距的传感器,获得了NO/SO_2两组分混合气体的敏感特性.与其他技术相比,最优传感器的灵敏度比现有技术高1—2个数量级,展示了三电极电离式碳纳米管传感器的应用潜力.

Compared with the traditional ionization sensor,triple electrode ionization gas sensor based on carbon nanotubes features excellent performances of small size and low operation voltage,and plays an important role in developing smart grids and the ubiquitous Internet of Things.However,they exhibit the disadvantages of small collecting current and low sensitivity,and need to be optimized in structure.Based on the Townsend discharge mechanism and three governing equations of particle mass conservation,electron energy conservation and Poisson equations,a two-dimensional plasma discharge fluid simulation model of the sensor is established by using the COMSOL Multiphysics software.According to gas composition,component concentration,structure of the sensor and voltage applied to the electrodes,we determine the chemical reaction,reaction rate coefficient,field control equation,initial values and boundary conditions.In order to calculate the interior distribution of charged particles inside the boundary,the inter-electrode space region is meshed.Initial values of mesh are set,such as a dense mesh of nano-meter length around the electrode having micro-nano structure,and a rough mesh of micro-meter length in the other region of inter-electrode space.The initial values of time-step are set for each mesh grid,and the discharge model of each mesh grid is numerically solved by the finite volume method.The three linkage governing equations are discretized and calculated iteratively in time and space,and the mesh values and time-steps are adjusted to make the results converged.The electrostatic field distribution and the average collecting current density of the eight kinds of sensors are obtained in the background gas of nitrogen.The optimal sensor structure is obtained by comparing the electric field intensities and current densities under different structure parameters.The eight kinds of the sensors are prepared for experimentally verifying the optimization method.The optimal structure of the 7#sensor has the highest collecting current density in the eight kind structures,which is consistent with the simulation results,and proves the feasibility of the structure optimization method proposed in the paper.Based on the optimal structure,the sensors,respectively with the electrode spacings of 100 and 120μm,are fabricated,and the response characteristics of NO/SO2 mixture gas are obtained.Compared with other technologies,the sensor with optimal structure exhibits 1-2 orders of sensitivity higher than the others.The optimized triple electrode ionization sensor based on carbon nanotubes exhibits many potential applications.