| Optical fiber hydrogen sensors have been currently a hot research topic because of their advantages, such as intrinsically safe, electromagnetic immunity, long signal transmission distance and small size. They have a great prospect and commercial value to be used in military and civilian fields. Limited to the poor performance of sensitive material, none of fiber optic hydrogen sensors can meet the actual measurement needs, even though a vaiety of types have been proposed in current studies. With the advances in micro-processing technology and low-dimensional materials synthesis methods, some of the characteristics of the fiber hydrogen sensor has been significantly improved, such as response speed and sensitivity. However, long-term stability, aging resistance, falling resistance to temperature drift and other key problems still exist to be solved. In this thesis, the main work are as follows:(1)A complete hydrogen adsorption model to palladium-based material is proposed, which concludes surface adsorption, subsurface exchange and bulk diffusion. Using the numerical method, the model has been solved to analysis the influcence to the saturated response rate of film and two typical spherical particles nanostructures, such as conditional temperature, hydrogen partial pressure, penetration depth and penetration rate of Pd-based materials. Research shows that the nanoscale materials present obvious size effects, the saturated time is greatly reduced because of the shorten of bulk phase diffusion time.(2)Pd92Y8 composite film of 30 nm thickness was prepared by magnetron sputtering. Thin film surface morphology, composition and crystalline state were studied by using a variety of characterization methods. The results show that film having a smooth surface and good crystalline. Factors for the degradation of the sensitive film worked in air at room temperature are analysised. A kind of thermal treatment process is proposed to recovery the aging film.(3)Pure palladium and palladium silver nanoparticles 5nm in diameter were prepared by liquid phase synthesis, and deposited by spin coating on the substrate. Characterization analysis shows a uniform particle size distribution can be obtained by this method with good dispersibility. This synthesis method can be used to fabricate palladium-based composite particles to regulate sensitive material properties.(4)Based on simulation results, the ambient temperature fluctuations will affect the saturation solubility of hydrogen sensitive materials, thus causing disturbance amplitude of the sensor response. This paper proposes a dual light path,method for temperature compensating temperature fluctuations. A sensor probe with adjustable intensity of the reflected light was designed. The rationality of the sensor system was verificed through experiments.In order to improve the sensor accuracy, low noise design based on the T-network preamplifier circuit was realized, using NI acquisition card and software to achieve the compensation algorithm data.(5)Base on the reflection type optical fiber hydrogen sensors, response performance of two kinds of sensor with palladium-yttrium nanofilms and palladium based nanoparticles were tested and analysed. Experimental results show that the response performance of the nano-film after aging in an air environment was significantly reduced. The heat treatment process can restore its sensitivity to hydrogen, improve the stability of the sensor and also suppressing drift. It was demonstrated that the liquid phase synthesis of nanoparticles can be used for the reflective type fiber optic hydrogen sensor system. |
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