Gas sensor for home-use

A miniaturised and mass-producible gas sensor is in development. It will allow household burners to adjust to changes in gas composition.

Gas spectrometers, equipment needed to analyse gas samples, used to be big and expensive. On a desk in Dr. Pelin Ayerden’s office in the EWI-building stands a classic example: larger than a shoebox and costing about as much as a small-sized car.

In the near future, when gas does not exclusively come from the Groningen gas fields anymore, every household will need some analysing equipment to evaluate the gas composition. Gas from Russia, Liquefied Natural Gas (LNG) or biogas all have various shares of methane, ethane, propane, butane, carbon dioxide, and nitrogen. They all differ from the present low-caloric Groningen gas, which consists of about 81% methane, 4% other hydrocarbons and 15% of nitrogen. Burners need to be adapted to the gas composition.

Clearly, a standard gas spectrometer in every house is not an option. Home equipment should be small, cheap and free of maintenance. Dr. Ayerden has developed the first step towards such a gas sensor based on optical absorption spectroscopy in her PhD research. The prototype sensor is as small as a stamp and it contains three units, so it can be made even smaller. Adding a light source and a detector would add to the thickness, however.

micro spectrometer
micro spectrometer

micro spectrometer

The micro spectrometer works on the basis of linear-variable optical filter or LVOF. Picture a tapered strip of glass inside which all wavelengths are quenched except one (depending on the local thickness of the glass). Incident white light on the top comes out as an evenly spaced spectrum at the bottom. With a layer of gas on top, an array of detectors under the LVOF measures spectral transmission, which is specific like a fingerprint for different gases.

Ayerden has miniaturised the LVOF gas sensor by placing the gas chamber not on top of the filter but in between two mirrors, one of which is slightly slanted (3.2 micrometres at one side and 3.4 at the other). To complicate things, the white ‘light’ is infrared radiation, and the IR light has to bounce to and fro dozens of times to attain discernible absorption in the gas.

home gas sensor
home gas sensor

home gas sensor

With this filter, Ayerden was able to distinguish between methane, ethane and propane by their different spectral absorptions. She concluded: “Therefore, the feasibility of a gas-filled LVOF has been demonstrated for the composition analysis of natural gas with actual gas measurements.”

An infrared light source has to be added on top and a detector array underneath to make the gas sensor complete. Better still, a data processing unit could be included on the same chip. That’s probably what a home gas sensor is going to look like. All solid state, the size of a 20 cents coin and dirt-cheap to mass produce. Future adjustable burners will use the sensor’s output to optimise the combustion in a changing world.

–> N. Pelin Ayerden, A Miniaturized Optical Gas Sensor for Natural Gas Analysis, PhD supervisors Prof. Albert Theuwissen and Dr. Reinoud Wolffenbuttel (EEMCS Faculty), July 5th 2016.

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