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

Contents 1 Key Issues 2 Types of microsensors 2.1 Optical fibre hydrogen sensors 2.1.1 Fiber Bragg grating coated with a palladium layer 2.1.2 Micromirror 2.1.3 Tapered fibre coated with palladium 2.2 Nanoparticle-based hydrogen microsensors 2.2.1 Thin film sensors 2.2.2 Thick film sensor 2.3 Diode based Schottky sensor 2.4 Enhancement 3 Calibration and lifetime 4 See also 5 External links

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.[1]

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 [2]. Palladium-based sensors have a strong temperature dependence which makes their response time too large at very low temperatures [3]. Palladium sensors have to be protected against carbon monoxide, sulfur dioxide and hydrogen sulfide.

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

Detects the hydrogen by metal hindrance

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

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

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).[4]

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 the increased number of conducting pathways.

• DOE Thin-Film research
• application thin film microsensor

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.

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.[5] A Pd/InGaP metal-semiconductor (MS) Schottky diode can detect a concentration of 15 parts per million (ppm) H₂ in air.[6] Silicon carbide semiconductor or silicon substrates are used.

Siloxane enhances the sensitivity and reaction time of hydrogen sensors.[7] Detection of hydrogen levels as low as 25 ppm can be achieved; far below hydrogen's lower explosive limit of around 40,000 ppm.

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

• Sensor
• Optical fiber
• Fiber Bragg grating
• Hydrogen leak testing

• Nanoparticle-Integrated Microsensor
• Fibre gratings for hydrogen sensing
• Wide-Range Hydrogen Sensor
• Bragg type optic fibre sensor
• Wireless sensor
• EU sensor sheet
• EERE succes story H2scan
• Argonne National Laboratory (Thin Film)