Small MagnetResearchers at the Fraunhofer Institute have developed a novelmagnetic sensor that they claim for the first time detects tinyfluctuations in a small magnetic field – even when there is astrong magnet right beside it. The sensor can therefore be utilised even in places where powercables generate an interference field – for instance, in acar’s side mirror. In the car mirror application, if there is a change of driver it isnormally required to adjust the position of the mirror and theseat. To provide automatic adjustment for each driver, a tiny chip in thekey or a corresponding button on the dashboard can be pressed,enabling all adjustment to be performed very easily. There is a tiny magnet in the mirror and another in the seat, whoseposition is detected by a magnetic sensor and which enables themirror to be correctly adjusted. The only problem with this systemis that the cables supplying the power for heating the mirror andcontrolling the stepper motor also generate a magnetic field. The sensor therefore sees not only the field generated by themagnet, but also that of the power cable – and errors can bemade. Up to now, therefore, such magnetic field sensors have had tobe screened. This is difficult and expensive. A new type of integrated 3-D magnetic field sensor from theFraunhofer Institute for Integrated Circuits (IIS) in Erlangen,Germany, can work without screening. The researchers have arrangedseveral sensors in a pixel cell in such a way that they can measureall three components of the magnetic field in one place. If two ofthese pixel cells are placed on a chip, the sensor measures notonly the magnetic field as such, but also how the position of themagnetic field changes. IIS team leader Dr Hans-Peter Hohe states:“This sensor enables us for the first time to identifymagnetic interference fields as such and to separate them from theuseful field. The sensor works perfectly even when the interferencefield is considerably larger than the useful field. There istherefore no need for shielding.”
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