EU project breakthrough for non-contact sensors

Non-contact position sensors are a small but vital part of machinery. Now researchers in an EU-funded project have used a phenomenon known as magnetoresistance to develop a practical, low-cost position sensor that performs better than existing designs. Commercial production will follow this year.

Electronic sensors that record the position of movable objects crop up in practically every machine, from printing presses to space rockets. The average modern car has more than 60 sensors to measure the positions of the crankshaft, throttle, clutch, suspension and dozens of other moving parts. These sensors need to be cheap (̈́4;0.5-5), yet very robust and reliable.

The oldest kinds of position sensor are mechanical switches and sliding resistors (potentiometers). Because they depend on direct electric contact, they are vulnerable to wear, corrosion and breakage, so modern designers tend to avoid them.

Instead, non-contact sensors based on magnetic phenomena are popular. In a non-contact sensor, a coil of wire (inductive and galvanometric sensors) or a semiconductor element ('Hall effect' sensor) detects the presence of a magnet mounted on another part of the machine.

But traditional magnetic sensors tend to be both insensitive and fairly expensive. And 'Hall effect' sensors have the additional disadvantage of being 'on/off' devices that cannot track the exact position of an object.

Partners in the MUNDIS project thought they could do better. And their results show they were right, with a market-ready product soon to follow. The EU-funded project developed more sensitive and cheaper position sensors based on magnetoresistance.

According to MUNDIS coordinator Professor Ricardo Ibarra an effect known as ballistic magnetoresistance (BMR) is particularly promising. Electrons have a property called spin (magnetic moment) that allows them to be influenced by a magnetic field as they fly between nanoparticles (hence "ballistic").

When a current passes through nanoparticles of iron oxide deposited on a plastic film, electrons are susceptible to BMR as they travel across nanocontacts between the nanoparticles.

The MUNDIS partners experimented with two different ways of making nanoparticles. The first route, which involves grinding iron oxide with a ball mill, yielded practical sensors that are both sensitive and reasonably cheap. The second method uses electrochemistry to deposit nanoparticles directly from solution.

"We have not finished developing the electrodeposition technique, but it is very promising,̶1; says Ibarra. ̶0;It can create devices that are even more sensitive and they should eventually be cheaper, too."

Image: Non-contact sensors are used in many types of machine, such as car engines

Source: ICT Results

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