Hydrogen microsensor

A hydrogen microsensor is a gas detector that detects the presence of hydrogen. Micro-fabricated point-contact hydrogen sensors are used to locate leaks.

Key Issues

There are four key issues with hydrogen detectors:

* Reliability: Functionality should be easily verifiable.
* Performance: Detection 0.5% hydrogen in air or better, response time < 1 second.
* Lifetime: At least the time between scheduled maintenance.
* Cost: Goal is $5 per sensor and $30 per controller. [ [http://www1.eere.energy.gov/hydrogenandfuelcells/pdfs/30535bb.pdf DOE requirements] ]

Types of microsensors

There are various types of hydrogen microsensors, which use different mechanisms to detect the gas. Palladium is used in many of these, because it selectively absorbs hydrogen gas and forms the chemical palladium hydride [ [http://www.innovations-report.com/html/reports/physics_astronomy/report-44815.html Palladium] ] . Palladium-based sensors have a strong temperature dependence which makes their response time too large at very low temperatures [ [http://adsabs.harvard.edu/abs/2005SPIE.5855.1000G response time] ] . Palladium sensors have to be protected against carbon monoxide, sulfur dioxide and hydrogen sulfide.

Optical fibre hydrogen sensors

Several types of optical fibre surface plasmon resonance (SPR) sensor are used for the point-contact detection of hydrogen:

Fiber Bragg grating coated with a palladium layer

Detects the hydrogen by metal hindrance

Micromirror

with a palladium thin layer at the cleaved end, detecting changes in the backreflected light.

Tapered fibre coated with palladium

Hydrogen will change the refractive index of the palladium, and consequently the amount of losses in the evanescent wave.

Nanoparticle-based hydrogen microsensors

The combination of nanotechnology and microelectromechanical systems (MEMS) technology allows the production of a hydrogen microsensor that functions properly at room temperature. The hydrogen sensor is coated with a film consisting of nanostructured indium oxide (In₂O₃) and tin oxide (SnO₂). [ [http://nsfreunano.research.ucf.edu/YearBook/Titans/2004/alvero.html Nanoparticle-based Hydrogen Microsensor] ]

Thin film sensors

A palladium thin film sensor is based on an opposing property that depends on the nanoscale structures within the thin film. In the thin film, nanosized palladium particles swell when the hydride is formed, and in the process of expanding, some of them form new electrical connections with their neighbors. The resistance decreases because of the increased number of conducting pathways. [ [http://www1.eere.energy.gov/hydrogenandfuelcells/pdfs/30535bb.pdf DOE Thin-Film research] ] [ [http://www.makelengineering.com/dir/Technologies/Hydrogen%20Detection/Hydrogen.htm application thin film microsensor] ]

Chemochromic hydrogen sensor

Reversible and irreversible chemochromic hydrogen sensors, a smart pigment paint that visually identifies hydrogen leaks by a change in color. The sensor is also available as tape. [ [http://www1.eere.energy.gov/hydrogenandfuelcells/pdfs/ht_ucf_raissi.pdf Chemochromic hydrogen sensor] ] [ [http://en.wikipedia.org/wiki/
] ]

Thick film sensor

Thick film hydrogen sensors rely on the fact that palladium hydride's electrical resistance is greater than the metal's resistance. The absorption of hydrogen causes a measurable increase in electrical resistance.

Diode based Schottky sensor

A Schottky diode-based hydrogen gas sensor employs a palladium-alloy gate. Hydrogen can be selectively absorbed in the gate, lowering the Schottky energy barrier. [ [http://www.electrochem.org/dl/interface/spr/spr06/spr06_p66-69.pdf Schottky energy barrier] ] A Pd/InGaP metal-semiconductor (MS) Schottky diode can detect a concentration of 15 parts per million (ppm) H₂ in air. [ [http://www.iop.org/EJ/abstract/0268-1242/18/7/303 Silicon carbide] ] Silicon carbide semiconductor or silicon substrates are used.

Enhancement

Siloxane enhances the sensitivity and reaction time of hydrogen sensors. [ [http://www.innovations-report.com/html/reports/physics_astronomy/report-44815.html Siloxane enhancement] ] Detection of hydrogen levels as low as 25 ppm can be achieved; far below hydrogen's lower explosive limit of around 40,000 ppm.

Calibration and lifetime

Sensors are calibrated at the factory and are valid for the service life of the unit.

See also

*Fiber Bragg grating
*Hydrogen analyzer
*Hydrogen leak testing
*List of sensors
*Optical fiber
*Sensor

References

External links

* [http://www.iso.org/iso/standards_development/technical_committees/list_of_iso_technical_committees/iso_technical_committee.htm?commid=531203 ISO TC 197 WG13]
* [http://www.epapers.org/sensors2006/ESR/paper_details.php?PHPSESSID=e489211df2f79f81e6ba8ecd6e9e7f11&paper_id=1622 Nanoparticle-Integrated Microsensor]
* [http://ej.iop.org/links/q63/,,,vhEqvhL1tjxru6ReiaQ/mst6_5_s31.pdf Fibre gratings for hydrogen sensing]
* [http://www.sandia.gov/mstc/technologies/microsensors/hydrogensensor.html Wide-Range Hydrogen Sensor ]
* [http://bit.or.at/irca/bbsshow8.php?ref1=OO/INTA/36&vQuelle=&bcc= Bragg type optic fibre sensor]
* [http://news.ufl.edu/2006/05/24/hydrogen-sensor/ Wireless sensor]
* [http://www.jrc.cec.eu.int/more_information/download/hydrogen%20safety%20sensors%20and%20their%20applications%20.pdf EU sensor sheet]
* [http://www.eere.energy.gov/industry/sensors_automation/pdfs/h2_monitoring.pdf EERE succes story H2scan]
* [http://www.anl.gov/techtransfer/pdf/HydrogenSensorr&d100.pdf Argonne National Laboratory (Thin Film)]
* [http://www.ika.rwth-aachen.de/r2h/index.php/Hydrogen_Sensor#_ref-0 Roads2HyCom]