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Modeling Analysis And Experimental Study On The Optical Fiber Hydrogen Sensor Based On Pd-based Alloy Thin Film

Posted on:2014-12-16Degree:DoctorType:Dissertation
Country:ChinaCandidate:Y LiuFull Text:PDF
GTID:1268330422462374Subject:Mechanical and electrical engineering
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With the industrial development, hydrogen sensors become very popular in the defense,military and civilian field. Unfortunately, existing hydrogen sensors have some disadvantageand can not satisfy actual demand. Due to the high safty and anti-interference, the fiberoptic sensor is a most application prospect sensor type in the hydrogen detecting field.Considering the problems in the research of hydrogen sensors, this thesis focuses on thesensing mechanism of the material, sensor design, the development of the high repeatabilityhydrogen sensor and the fast hydrogen sensor. The main work as follows:(1) A reflected model of films basd on optic matrix is proposed. It shows how therefractive index, thickness, substrate material and the wavelength of the incident lightinfluence the reflectivity of the film.(2) A hydrogen atomic diffusion model in the films is proposed. It shows therelationships between the concentration of hydrogen atoms and the diffusion time, the filmthickness.The response time of sensors is proportional to the square of the film thicknessaccording to the results of the simulation analysis.(3) A hydrogen bubble model is proposed to explaim the failure of films, according tothe micro-observation to the film. It shows how the delamination height, refractive index,thickness, substrate material, the incident light wavelength influence the repeatability of thefilm.(4)A reflection coupled model of the optical fiber bundle is proposed. The simulationstudy shows the influence of the transmission fiber core diameter, receiver fiber core diameter,reflective distance and numerical aperture on the reflectivity of films. Coupling model isverified by experiments. The optimum reflection distance is discussed for the reflected-typedfiber hydrogen sensor.(5) To improve the accuracy of the hydrogen sensor, this thesis analyzes the principle ofphotodiodes, designs a preamplifier circuit based on the T-network to eliminate the outputoffset voltage, a matlab filtering procedures based on wavelet transform method to eliminatethe influence of noise and improve the SNR of sensors.(6)According to the deeply analysis of films failure mechanism, the thesis first-ly explain the principle of the crack inhibited by doping in Pd and proposes a doping methodof the Pd-based alloy film based on DFT theory for hydrogen sensing. By using this method, ahigh repeatability hydrogen sensor prototype is fabricated and tested.The experimental resultsshow that the PdY alloy film can improve the repeatability of hydrogen sensors and theH-induce aging treatment can imporove the repeatability of new films. The drifts of the zeropoints and hydrogen points are smaller than0.2%after aging treatment. The sensors have ahigh practical value. (7)According to the analysis results of hydrogen atoms diffusion model in films, a fasthydrogen sensor based on ultrathin nano-film is proposed and tested. The experimental resultsshow that the10nm Pd/PdY composite film has a fast response performance. The shortestresponse time and recovery time is6s and8s for4%H2. A loading/unloading cycle is notmore than16s. Compared with other fiber hydrogen sensors reported, it possesses obviouslysuperiority.
Keywords/Search Tags:fiber sensor, reflected-typed sensor, hydrogen sensor, Pd-based alloy film, nano-film
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