Design and Development of a Low-Cost Fiber-Optic Hydrogen Detector

    Research output: Contribution to conferencePaper


    A cost-effective detector for hydrogen gas leaks will be needed in many hydrogen-fueled technologies of the future. In particular, the hydrogen-fueled automobile may require hydrogen leak sensors in several locations and their cost could be prohibitive if conventional sensor techology is used. This project is directed at the development of low-cost fiber-optic (FO) hydrogen gas detectors thatcould provide adequate sensitivity, response speeds and reliability in an automobile application. The FO sensor relies upon a reversible chemical reaction between gaseous hydrogen in air and a thin film of tungsten oxide. The initial sensor design consists of a thin tungsten oxide film coating on the flat end of a polymer or glass optical fiber. A very thin overcoating of palladium catalyzes thereaction between the hydrogen and the tungsten oxide and reflects a light beam back along the optical fiber to a light intensity monitor. When the hydrogen reacts with the coating, the tungsten oxide becomes optically absorptive and attenuates the reflected light. The sensitivity and response speed of this sensor were studied over a range of temperatures and found to be too slow for the intendedapplication. A new, faster sensor design was invented that relies upon the resonant absorption of light at a beveled facet on the end of the optical fiber. The resonance occurs when the incident light strikes the metal coated facet at an angle just above the critical angle for total internal reflection. The evanescent wave stimulates resonant absorption by free electrons in the metal to producea so-called surface-plasmon (SP). An overcoat of thin tungsten oxide on top of the metal film is designed to provide an optical wave-guide for light at the SP resonance. The two layer coating produces a coupled resonance at the SP wavelength that is very sensitive to the optical constants of the tungsten oxide. When hydrogen reacts with the tungsten oxide the resonance frequency shifts and thisshift is detected in the spectrum of the reflected light beam. The facets are angled at 45 degrees to the fiber axis so as to reflect the light back along the fiber with a doubling of the SP absorption from the double reflection. A facet perpendicular to the fiber axis produces a reflected signal that is not affected by hydrogen that is used as to produce an internal reference signal forcomparison to the resonance, hydrogen-sensitive signal. The ratio of these two signals cancels out noise due to variation in the transmittance of the optical fiber. A patent application has been filed for this new design and a small business partner has formed a CRADA with NREL to develop a commercial detector based upon it.
    Original languageAmerican English
    PagesVol. II: 605-624
    Number of pages20
    StatePublished - 1996
    Event1996 U.S. DOE Hydrogen Program Review - Miami, Florida
    Duration: 1 May 19962 May 1996


    Conference1996 U.S. DOE Hydrogen Program Review
    CityMiami, Florida

    NREL Publication Number

    • NREL/CP-22546


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