A SMART tyre that tells drivers when it needs replacing or inflating has been developed by engineers in the US.

Instruments that tell drivers the condition of their tyres are already available, but they are expensive and unreliable, says Wen Ko, an engineer at Case Western Reserve University in Cleveland, Ohio. So Ko and a team at Goodyear led by William Dunn have designed and patented tiny temperature and pressure sensors using microscopic components known as microelectromechanical systems (MEMS).

Ko says sensors built with MEMS technology are reliable, cheap and remain stable over the life of the tyre-up to 10 or 12 years. The pressure sensor is a tiny capacitor made from two parallel silicon plates. The thinner top plate changes shape depending on the pressure of air in the tyre, which produces a measurable change in the capacitance of the device.

The temperature sensor is made from semiconductors that change their resistance to current flow as their temperature changes. These sensors, together with a transponder, are incorporated into the wall of the tyre during manufacture.

Each tyre also contains an ID chip that helps tyre makers keep track of their stock. To identify a tyre, or read its temperature or pressure, a radio signal is sent out by a transmitter built into a vehicle or a handheld scanner. The incoming signal provides enough power for the transponder to run the sensors and beam back the tyre's vital statistics.

While Goodyear has successfully tested the sensors in truck tyres, it refuses to reveal when the tyres might reach the marketplace.

Kevin Delaney of the Traffic and Road Safety department of Britain's Royal Automobile Club says the devices could be useful, as motorists rarely check their tyres.

Author: Ben Crystall
New Scientist magazine, issue 13th Feb 1999

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