Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Position sensors: magnets know their place

28.02.2008
Non-contact position sensors are small but important parts of many modern machines. Researchers 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 (€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.

Introducing magnetoresistance
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. This phenomenon, which describes how a magnetic field changes the electrical resistance of certain materials, has been known since the nineteenth century, but until recently had no industrial applications.

‘Giant magnetoresistance’ (GMR) was discovered in 1988 and now finds application in computer hard disks. Both GMR and another effect known as thin-film magnetoresistance (TMR) could be used for position sensors. According to MUNDIS coordinator Professor Ricardo Ibarra, however, GMR and TMR are the province of large companies, because they require huge investment in cleanrooms and other equipment developed for the semiconductor industry.

More promising for the EU-funded MUNDIS, Ibarra says, was an effect known as ballistic magnetoresistance (BMR). 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,” says Ibarra. “It can create devices that are even more sensitive, and they should eventually be cheaper, too.”

Vertical focus
From the start, MUNDIS aimed to create a practical BMR device: a gear stick position sensor for the automotive industry. This is a four-position ‘on/off’ sensor with a target cost of €5, falling to €4 with bulk production.

By January 2008, three months before it was due to finish, the project had shown excellent results. The partners had developed all the parts needed for a complete gear stick position sensor: the film-based sensor itself, the associated printed circuit board, and a magnet carrier. Tests showed that the device can operate reliably for 10 million cycles, as well as withstanding vibration, humidity and thermal stress.

The technology is patented and licensed to two Spanish SMEs who were partners in the project. Aragonesa de Componentes Pasivos (ACP), a manufacturer of electronic components including position sensors, makes the sensor material. Ficosa International, which makes automotive components and systems, then assembles the complete sensor. The cost is even lower than the original target, and the new sensors will be on the market within a few months, Ibarra says.

Tasks remaining to be done include improving control of the initial resistance of the sensor material, and gaining a better understanding of what happens within the nanostructure.

“Although the sensors work well, it may be that not all of the magnetoresistive effect in fact comes from BMR,” says Ibarra. To study the mechanism of BMR in detail, the researchers are now using a focused ion beam to build tiny circuits, less than 1 µm in size, involving just a few nanoparticles.

The sensors can be made in almost any shape, Ibarra says, and in principle there is no lower limit to their size. Since smaller sensors are expected to work better than large ones, some innovative applications might emerge.

One exciting potential application is in biosensing. “If we could get a magnetic nanoparticle to stick to a microorganism, then we could use a BMR sensor to detect the magnetic particle and hence the organism,” Ibarra suggests. This is clearly a technology with potential.

Christian Nielsen | alfa
Further information:
http://cordis.europa.eu/ictresults/index.cfm/section/news/tpl/article/BrowsingType/Features/ID/89583

All articles from Power and Electrical Engineering >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Data use draining your battery? Tiny device to speed up memory while also saving power

The more objects we make "smart," from watches to entire buildings, the greater the need for these devices to store and retrieve massive amounts of data quickly without consuming too much power.

Millions of new memory cells could be part of a computer chip and provide that speed and energy savings, thanks to the discovery of a previously unobserved...

Im Focus: An energy-efficient way to stay warm: Sew high-tech heating patches to your clothes

Personal patches could reduce energy waste in buildings, Rutgers-led study says

What if, instead of turning up the thermostat, you could warm up with high-tech, flexible patches sewn into your clothes - while significantly reducing your...

Im Focus: Lethal combination: Drug cocktail turns off the juice to cancer cells

A widely used diabetes medication combined with an antihypertensive drug specifically inhibits tumor growth – this was discovered by researchers from the University of Basel’s Biozentrum two years ago. In a follow-up study, recently published in “Cell Reports”, the scientists report that this drug cocktail induces cancer cell death by switching off their energy supply.

The widely used anti-diabetes drug metformin not only reduces blood sugar but also has an anti-cancer effect. However, the metformin dose commonly used in the...

Im Focus: New Foldable Drone Flies through Narrow Holes in Rescue Missions

A research team from the University of Zurich has developed a new drone that can retract its propeller arms in flight and make itself small to fit through narrow gaps and holes. This is particularly useful when searching for victims of natural disasters.

Inspecting a damaged building after an earthquake or during a fire is exactly the kind of job that human rescuers would like drones to do for them. A flying...

Im Focus: Topological material switched off and on for the first time

Key advance for future topological transistors

Over the last decade, there has been much excitement about the discovery, recognised by the Nobel Prize in Physics only two years ago, that there are two types...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

ICTM Conference 2019: Digitization emerges as an engineering trend for turbomachinery construction

12.12.2018 | Event News

New Plastics Economy Investor Forum - Meeting Point for Innovations

10.12.2018 | Event News

EGU 2019 meeting: Media registration now open

06.12.2018 | Event News

 
Latest News

Data use draining your battery? Tiny device to speed up memory while also saving power

14.12.2018 | Power and Electrical Engineering

Tangled magnetic fields power cosmic particle accelerators

14.12.2018 | Physics and Astronomy

In search of missing worlds, Hubble finds a fast evaporating exoplanet

14.12.2018 | Physics and Astronomy

VideoLinks
Science & Research
Overview of more VideoLinks >>>