A new optical-fiber hydrogen sensor has been developed.The sensor utilizes the absorption change of the evanescent field in the clad region.Th eplationum or palladium supported tungsten oxide film prepared by the sol-gel process was used as the clad.In the presence of hydrogen,strong evanescent-wave absorption was observed as a results of the formation of tungsten breonze.The sensor sensitively and immediately responded to hydrogen even in the low concentration range.It was found that the characteristics of the sensor were easily controlled by the amount of catalysts.The sensor developed in this study has potential to measure the spatial distribution along the fiber line,unlike the traditional hydrogen sensors that measure the concentration fo a certain spatial point.
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