Research On An Optical Fiber Hydrogen Sensor For Enhanced Sensitivity With Multi-Layer Au-Pd Core-Shell Nanoparticles Film

Hydrogen has become one of the most important clean energy carriers in the 21~stt century with it's unique advantages.While in the process of the hydrogen production,storage,transportation and refueling,hydrogen is easily to leak out and causes serious accidents as its lively chemical properties.Therefore hydrogen's leakage monitoring is indispensable.The optical fiber hydrogen sensor is a kind of sensor that uses light as the information transmission medium for hydrogen concentration.It has been currently a hot research topic because of their advantages,such as intrinsically safe,electromagnetic immunity,long signal transmission distance and small size.It's suitable for real-time monitoring of hydrogen concentration in a variety of dangerous and complicated environments.At the present,the optical fiber hydrogen sensor mainly utilizes the Pd or its composite thin film material after absorbing the hydrogen the physical properties(such as refractive index,reflectivity,volume)changes to modulate the intensity,the wavelength and the path of the optical signal to realize the perception of hydrogen concentration information in the environment.But these sensors are limited by the diffusion of hydrogen in the film layer,making the sensor's sensitivity and response speed exist irreconcilable contradictions.In this paper,aiming at the problems existing in the research of optical fiber hydrogen sensors,a multi-layer transmissive optical fiber hydrogen sensor equipped with Au-Pd core-shell nanoparticle film was proposed.While ensuring the high response speed of nanoparticle films,the sensitivity of hydrogen can be increased by increasing the number of the films to increase the number of modulation times of light intensity so as to achieve the coordination and optimization of the sensitivity and the response speed.The main works of this paper are as follows:1)Establishing the theoretical model of the transmitted light intensity with single-layer core-shell nanoparticles film,analyses the influence of the thickness of the Pd shell and the coverage of the nanoparticle film on the transmitted light intensity,and analyses the change of the transmitted light intensity caused by the change of the dielectric constant before and after nanoparticles film absorbing hydrogen.2)Nanoparticles of Au-Pd core-shell structure with small particle size and narrow size range were prepared by seed growth method,and were uniformly dispersed on glass substrate by centrifugal deposition method.The composition and morphology of nanoparticles were studied by a variety of characterization methods,and measure the thickness and coverage of the nanoparticle film.The performance parameters of the nanoparticle film which affect its response characteristics were tested through a reflective sensing experiment platform.3)A multi-layer transmission optical fiber hydrogen sensing system with high degree of automation and integration,low noise and high stability was designed.Established sensitizing effect theoretical model of multi-layer nanoparticles film,and revealing the number of films and the transmissive of nanoparticles film on the sensitizing effect of the sensors.4)Based on the multi-layer transmission type optical fiber hydrogen sensors,experiment research for the performance of multi-layer transmission optical fiber hydrogen sensor which equipped with different Pd shell thickness and different numbers film,not only investigates the effect of nanoparticle thickness and number of films on response characteristics,but also verify this sensor can achieve the coordination of response speed and sensitivity optimization.The sensor was tested for continuous hydrogen release at room temperature and pressure,analyses the sensitivity,stability and repeatability of the sensor,the results shows that the sensor has good practical value.