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3D Hall sensor offers precision position measurement

Posted: 12 Jun 2013 ?? ?Print Version ?Bookmark and Share

Keywords:Hall sensors? magnetic field measurement?

Magnetic field measurement, though useful in many ways, remains imprecise and susceptible to interference. Conventional sensors used are cost-effective and robust yet they generally measure only the magnitude of the magnetic field perpendicular to the chip surface.

Such limitations prompted Michael Hackner, Dr.-Ing. Hans-Peter Hohe, and Dr.-Ing. Markus Stahl-Offergeld of the Fraunhofer Institute for Integrated Circuits IIS to develop a 3D Hall sensor that provides precise position measurement with the advantages of magnetic field sensors.

"First we connected up several sensors on a chip in order to improve the measuring accuracy of the individual sensors," says Stahl-Offergeld. "Next we arranged several of these sensors to measure the three-dimensional magnetic field at one point. The result was our pixel cells." Thus, a new generation of 3D Hall sensors was born, capable of measuring all three spatial axes of a magnetic field and calculating the exact position of an object.

HallinOne magnetic sensor

HallinOne magnetic sensor. (L-R) Stahl-Offergeld, Hohe and Hackner claim it can measure exact position.

The sensor chip contains a designated sensor for each of the three magnetic axes. These sensors are placed together in the pixel cell and attain a resolution of just a few microteslas depending on the measurement speed. Tesla is the unit for magnetic flux density. Also integrated directly on the chip are the evaluation circuit and a coil, which enable self-testing and calibration. Hohe points out that "HallinOne" magnetic sensor can be manufactured via standard semiconductor production processes despite its complexity.

"Our next goal is to develop a sensor for 5-axis position measurement," says Hackner. "This will allow us to detect more mechanical degrees of freedom simultaneously, including translatory and rotary movements by the magnet in all directions. It already works in laboratory tests, but the system still needs some adjustments before it is ready for real-life applications." Such applications could include use in the control systems of computers, construction machines, robots and airplanes.

One of the first companies to exploit the potential of HallinOne was German firm Seuffer. As far back as 2006, it launched a sensor that prevents washing machines from wobbling and creeping across the floor during spin cycles. A magnet is attached to the tub and the sensor to a fixed, unmoving part of the washing machine. Depending on how much washing is in the drum and how it is distributed during a spin cycle, the tub moves and therefore the magnet, too. The sensor measures this movement, evaluates the data, and transmits it to the washing machine. If the drum is wobbling, it is stopped briefly and shaken around a bit in order to distribute the washing more evenly.

Fraunhofer IIS and Seuffer are currently developing a wireless window sentinel, which detects whether a window is open or closed and transmits this information via a wireless sensor network combined with energy harvesting.

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