MEMS bridges lead to e-nose

Belgian research institute IMEC and its affiliate Holst Centre in the Netherlands have developed a technology for so-called e-noses that the developers claim is cheaper to make and offer greater sensitivity than other micromachined technologies.

Comparing the IMEC/Holst e-Nose to IBM’s cantilever, researcher Mercedes Crego-Calama claimed the sensor can be made much smaller and consumes less power because the IBM system needs a laser to detect changes in vibration caused by the adsorption of gas molecules onto the beams.

Crego-Calama claimed cantilever systems such as IBM’s are better at detecting heavy molecules. The beams in the e-Nose design are supported at both ends, with a piezoelectric ‘shaker’ used to excite the beams. The changes in vibrations are sensed at the opposite end.

Polymers attract different gas molecules. The ability to detect different gases depends on the number of beams and which polymers are used – each selecting for a different type of gas. “Vapours adsorb [changing the beam’s mass] and cause swelling, which stresses the beam,” said Grego-Calama. “Both factors work in the same direction and lower the vibration frequency.”

The group is working to improve the packaging and to work out how the sensor is affected by temperature changes. “We need to study how susceptible it is to temperature,” she said.

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