A prototype of leak detector that can detect a 1% concentration of hydrogen in air with a response time of less than one second has been developed by the Electromagnetism and Telecommunications Department of the Faculté Polytechnique de Mons in Belgium and the research center Material Nova from Mons, also.

  

In the past, fiber Bragg gratings (FBGs) covered with palladium have been widely investigated for hydrogen sensing, where the sensing mechanism is based on the swelling of the palladium coating, resulting in a stress on the grating. In practice, the palladium-coated sensors suffer from a variety of problems, including a long response time and measurements affected by hysteresis. The most important limitation is their non-correct operation in air environment. This is a major issue since many applications such as the monitoring of stocking reservoirs and pipes require the use of hydrogen sensors in air.

 

To solve these problems, a new sensor design was demonstrated by the Mons team where FBGs were covered with a catalytic sensitive layer. This was made from tungsten oxide powder doped with platinum. In the presence of hydrogen in air, the sensitive layer takes part in an exothermic reaction and induces a temperature elevation around the FBGs that is measured through a shift of their central wavelengths so that a straightforward interrogation set-up can be used.

  

The sensor prototype has a linear response to varying hydrogen concentrations. This linear response is reversible, so there is no need to recondition the sensor after hydrogen detection. A good sensitivity is obtained whatever the relative humidity level of the air. A good operation was also demonstrated for ambient temperatures down to -50 °C. Finally, the sensor design is also compatible with frequency multiplexing systems and can be used in quasi-distributed sensors.

 

More information:

C. Caucheteur, M. Debliquy, D. Lahem, and P. Mégret, "Hybrid fiber gratings coated with a catalytic sensitive layer for hydrogen sensing in air," Opt. Express 16, 16854-16859 (2008).

 

http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-16-21-16854