Gas alert

摘要

A sensor that uses pressure waves to detect the concentration of gas could provide government agencies and industry with a solution for tracking emissions such as carbon dioxide that is smaller and cheaper than alternatives. The developers hope that in three years they will have a sensor that is less than 2cm long and at least twice as sensitive as other sensors of its size. The MINIGAS project, a consortium led by VTT Technical Research Centre of Finland, is backed by €2.8m (￡2.2m) from the European Union. The sensor collects air samples inside a chamber and tests the concentration of gas, using the principle that different gases absorb different wavelengths of light. The system uses a diode laser as a light source. At a specific wavelength the carbon dioxide absorbs light, heats up and the increase in temperature creates pressure inside the sample. Pressure waves then move a silicon cantilever, which swings like a cat flap inside the device, and its movement is measured with a laser interferometer. The amount of displacement depends on the intensity of the pressure wave, which is deter-rnmined by the concentration of gas. Other gas sensors use a similar photoacoustic principle, in which light waves are turned into pressure waves. But they rely on the waves producing a sound that can be detected with a microphone, measured and used to ascertain the concentration of any gases.