Signalling a breakthrough

A microsensor invented at Oxford University could dramatically reduce engine emissions and improve car braking systems, its developers claimed this week.

It also has potential applications in searching for landmines and buried fibre optic cables.

The magnetic sensor, small enough to be fitted on to a microchip, has been designed primarily to monitor position or speed of components in car suspensions, gearboxes and engines.

The device has already undergone trials in the distributor of a Daimler-Benz V8 engine, where it was used to control the ignition timing. Unlike existing devices, it can tolerate temperatures of over 1000 degrees C for long periods of time, and eliminates misfires at low engine speeds, meaning hydrocarbon emissions are reduced.

The sensor, which if produced in volume on microchips would cost only 30p – 40p, is based on an RF antenna coiled around a very fine tube, which produces anelectromagnetic field. The antenna is driven by a small oscillator, and is connected to an electronic circuit monitoring the field.

When an object is brought into proximity with the antenna, it reacts with either the electric or magnetic fields and changes the resonance charge of the antenna and oscillator. This change is detected by the electronic circuit, which produces a signal.

In car braking systems, the sensor can detect changes at wheel speeds down to zero rpm, unlike conventional sensors where the performance drops as the speed is reduced, said Dr John Gregg, the device’s inventor.

‘Existing braking systems use variable reluctance (VR) sensors, and their output tends to be zero as the wheels lock, which is exactly what you don’t want with an ABS system. The output of this sensor is speed independent,’ said Gregg.

The device, which is subject to a patent application by Oxford University’s technology arm Isis Innovation, can also be used for condition monitoring of lubricating oil within car engines, and is able to detect when the oil needs changing.

The sensor can detect or monitor a wide variety of materials, such as ferrous or non-ferrous metals and ceramics. The device can also tell the difference between plastics and glass, and researchers are investigating its potential use for detecting underground fibre optic cables and plastic landmines.

To detect buried plastic materials, the sensor must be mounted on a probe and inserted into the ground. This process means the sensor is moving in relation to the plastic cable or landmine, which affects its electromagnetic field, and causes a signal to be detected.