Research On Fiber-optic Surface Resonance Hydrogen Sensor Based On Pd-Ag Coating

As a renewable and infinite recycling energy, hydrogen has attracted more and more attention. However, due to strong penetrability, flammability, explosive, hydrogen can easily cause potential safety problems and trigger off major security incidents. Explosion are easily caused while the hydrogen concentration ranging from4%to74.5%upon normal temperature and pressure conditions. Combining the SPR sensor technology of a higher sensitivity with the optical transmission technology having low rate of energy loss, Fiber-optic SPR sensor technology has been widely used for sensing because of its good insulation, anti-electromagnetic interference, resistance to corrosion, safety, high sensitivity, light weight, small size, miniaturization, low cost, well reusability, real-time detection and other advantages. In this paper a new fiber-optic surface resonance hydrogen sensor based on Pd-Ag coating is produced and discussed, which have a high sensitivity to hydrogen concentration changes.In this thesis, simulation shows that with the increases of the refractive index of sensing area, effective refractive index of the SPR mode of metal-coated side-polished "D" shape fiber increases; while with the increases of the and the thickness of metal coating the effective refractive index of the SPR decreases.The structure of SPR sensing probe is designed according to detection principle of SPR hydrogen sensor, which is comprised of double layer. The first layer is Ag whose thickness is4nm, while the second layer is26nm Pd-Ag composite (the proportion of silver and palladium is about1:3). Two kinds of methods achieving side-polished optic fiber are comparatively introduced. Preparation craft of hydrogen sensitive films achieved by using magnetron sputtering is studied in the thesis. Through specific experiments and comparison of the change with hydrogen concentration of transmission power of optical fiber hydrogen sensors which are separately deposited with single Pd film, Pd-Ag co-sputtering composite films, we find that optical fiber hydrogen sensor based on Pd-Ag composite film is better than single Pd film in sensitivity, response time, linear relation and repeatability. When the hydrogen concentrations are4%, transmission power of Pd-Ag composite film changes as high as120nW, while that of single Pd film changes60nW. Experimental results show that side-polished FBG hydrogen sensor coated with Pd-Ag film has good sensitivity, reproducibility and stability. When the hydrogen concentrations are4%, the Bragg wavelength of FBG shifts towards the short wavelength for about90pm. When we placed the side-polished FBG sensing probe in liquids with different refractive indexes, the transmission wavelength shifts towards short wavelength with the increases of the surrounding refractive indexes. Finally, we sum up the full text and put forward the outlook of the work of the next step.