Research On A New Optical Fiber Hydrogen Sensor With Multi-Layer Pd-Y Alloy Nano-Thin Film

In the process of the production,transport and use,hydrogen is extremely easy to leak out,causing fire and explosion accidents as its lively chemical properties.People has developed a variety of sensing devices for hydrogen leak detection,in order to maximize reduce the security risk in the process of transport,storage and use of hydrogen.In the existing hydrogen sensor,a new type of optical fiber hydrogen sensor base on optical fiber sensing technology has a number of incomparable merits as conventional detection technology.The mainly theory of optical fiber hydrogen sensor is that measuring the material's changes of optical or mechanical properties after metal palladium membrane absorb hydrogen,which reflect the hydrogen concentration.The reversible chemical reaction between palladium and hydrogen is the essential principle of optical fiber hydrogen detection.Reaction time determines the response time of the sensor,and the extent of reaction determines the concentration of hydrogen.Traditional film model of optical fiber hydrogen sensor is subject to the hydrogen diffusion in the membrane layer,while increasing film thickness to increase sensitivity,it is bound to reduce the response speed of the sensor.Reduce the film thickness can reduce the diffusion time of H atom inside the membrane,and improve the response speed,but the too thin Pd membrane's optical and mechanical properties changes very weak after hydrogen absorption,so as to reduce the measurement sensitivity.And too thin Pd films will have a serious impact on the mechanical strength and reliability of the sensor,result in failure problem of film delamination and cracking,etc.In order not to affect the response speed of the hydrogen sensor,and also enhance the sensitivity of the sensor,this article was improved on the structure of the transmission type optical fiber bundle hydrogen sensor,has designed a new transmission-type optical fiber hydrogen sensor with multi-layer palladium/yttrium(Pd/Y)alloy films.The sensor designed with the structure of transmission type optical path,several pieces of Pd/Y alloy films arranged in a line,forming the multilayer transmission type optical fiber hydrogen sensor,the structure can increase the sensor's sensitivity by increasing the number of films,and improve the response speed by reducing the film thickness,that realized independent optimization between the sensitivity and fast response of the optical fiber hydrogen sensor.In this dissertation,the main works are as follows:1)the theoretical research of the multi-layer transmission optical fiber hydrogen sensor,it analyzes the sensor's probe structure model and double light path compensation structure model,analyses the change of Pd membrane's refractive index before and after metal Pd absorb and release hydrogen acordding to Drude model,establish optical model of transmission optical fiber hydrogen sensor.2)the structure design of multi-layer transmission optical fiber hydrogen sensor,such as the preparation of palladium yttrium alloy nano-film,the structure design of the sensor probe,the structure design of the gas circuit,the design of signal detection and acquisition and data processing method,etc.3)experiment research for performance of multi-layer transmission optical fiber hydrogen sensor,such as using atomic force microscope to measure the morphology and thickness of the prepared Pd/Y alloy thin films,the results shows that Pd/Y films has good uniformity.It tests the response time and sensitivity of multi-layer transmission optical fiber hydrogen sensor with experiments under atmospheric pressure and temperature,carries out the sensor's response stability and repeatability experiments,and related experiment contrast and research to the sensor's spectral characteristics,etc.