Study On Making Process And Detection Method Optimization Of Optical Fiber Evanescent Wave Hydrogen Gas Sensor

Traditional semiconductor hydrogen gas sensor has been invited and made a greatcontribution to space technology and research. But the applied voltage in traditionalsemiconductor hydrogen gas sensors would lead to explosion, which resulted in somelimitation in its applications. However, the optical-fiber sensor, which detects opticalsignal, does not cause spark and has various advantages, such as high precision, simpleprocess, low cost, resistant to electromagnetic interference and easy operation in remotedetection etc. Thus, it becomes a better choice for hydrogen gas detection, and theresearch in this field has gradually become hot in recent years both at home and abroad.And the optical fiber evanescent wave hydrogen gas sensor was one of the rapiddeveloping optical fiber sensor and has good application prospects, as it was able toachieve distributed sensing through Optical Time Domain Reflectometer, which couldbe used for real-time multi-point monitoring. The working principle of optical fiberevanescent wave hydrogen gas sensor was based on the change of optical properties,such as refractive index which would cause a variation of optical power absorption ofevanescent field after the Pd/WO3hydrogen sensitive film exposing into the hydrogengas. And the optical power variation in sensor was used for detecting the hydrogen gasconcentration.The research of optical fiber evanescent wave hydrogen gas sensor consists ofmaking process and signal detection method—such as selection of hydrogen sensitivefilm, research of sensing mechanism, design of sensor structure, analysis of light wavepropagation, contrive of signal detection system, optimization of detection method etc.The fundamental structure and working principle of step-index single mode opticalfiber sensor were introduced. Then, mathematical models were established by usingwaveguide theory, and therefore, detection method was optimized and the impacts onperformance caused by main parameters were analyzed through simulation. The makingprocess—such as preparation process of Pd/WO3hydrogen sensitive film and sensorstructure etc. was introduced. The specific contents in this work were as follow:①Introduction of basic principles of optical fiber evanescent wave hydrogen gassensor—introduce the basic principles of optical fiber evanescent wave hydrogen gassensor.②Detection method optimization of optical fiber evanescent wave hydrogen gas sensor—propose a new detection method, which is able to improve the relative variationfor nearly9times by detecting the variation of optical power in the evanescent fieldthrough mathematical analysis and simulations; analyze the impacts on performancecaused by main parameters through simulation.③Research of removing the fiber cladding through experiments—introduce thecorrosion principle; research the relationship between HF concentration and corrosionrate through experiments.④Preparation of Pd/WO3Sol—research the Pd/WO3Sol preparation process, theimpacts of H2O2, C2H5OH and temperature on Pd/WO3Sol stability throughexperiments, and relationship between aging time and Sol viscosity.⑤Experiments of film coating process—prepare the PdWO3film by dip-coatingmethod, plate the Ag film by Electroless plating; and result shows plating time shouldbe about60min.⑥Testing of hydrogen gas sensitivity—establish the testing system and do the gassensitivity experiments.