New magnetic sensor remains unhindered by interference field

Washington, June 4 : Scientists at the Fraunhofer Institute for Integrated Circuits IIS in Erlangen have created a new type of integrated 3-D magnetic field sensor that can tiny fluctuations in a small magnetic field, even when there is a strong magnet right beside it.

The researchers say that their innovation can be utilized even in places where power cables generate an interference field, such as in a car's side mirror.

They say that sensors accurately register the slightest temperature fluctuations, the tiniest changes to a magnetic field, or barely perceptible air currents.

However, there are limits to their accuracy, as in a case where a sensor is supposed to register a small fluctuation to a magnetic field in a place where a strong magnetic field already exists.

Giving the example of the sensors in a car mirror, they said that the seat and the mirror usually require readjustment whenever there is a change of driver.

They said that it would be easier if the position of the seat and the mirror could be saved individually for each driver, and the driver could move them into the correct position with the aid of a chip in a button on the dashboard.

They said that a magnet would be placed each in the seat and mirror to detect their positions by a magnetic sensor, so that they could be correctly adjusted.

The researchers said that the only problem to date with the system was that the cables supplying the power for heating the mirror and controlling the stepper motor also generated a magnetic field, due to which the sensor saw the fields generated by the magnet and the power cables, and came to the wrong conclusions.

It is due to this reason that magnetic field sensors have had to be screened to this day in a difficult and expensive procedure.

The Fraunhofer researchers insist that their new magnetic field sensor can work without screening.

For making it, the researchers have arranged several sensors in a pixel cell in such a way that they can measure all three components of the magnetic field in one place.

If two of these pixel cells are placed on a chip, the sensor measures not only the magnetic field as such, but also how the position of the magnetic field changes.

"This sensor enables us for the first time to identify magnetic interference fields as such and to separate them from the useful field. The sensor works perfectly even when the interference field is considerably larger than the useful field. There is therefore no need for shielding," says IIS team leader Dr. Hans-Peter Hohe

The sensors are also suitable for high-temperature applications up to around 150 degree Celsius, and thus can be utilized in places such as the engine compartment.

They have already been tested to be suitable for industrial use.

The researchers are using low-cost standard CMOS techniques to facilitate serial production of the sensors.

ANI