Switching and measuring with unique precision

Simple magnetic field sensors have been on the market for over 50 years. However, they can perceive movements in only two dimensions – for example, when a magnet moves past from left to right, or when it comes closer to or moves further away from the sensor. Complex movements as in the satnav button of the future are beyond its capabilities. “Thanks to the four pixel cells, we’re now able for the first time to measure the movements of a magnet in all six dimensions,” Hohe emphasizes – first, in the x, y and z directions, which is to say forward and back, left and right, up and down; and second, rotation around these three axes. “That means we can fully capture the movement of a magnet, which opens up many new application areas,” Stahl-Offergeld adds. The technology is based on something called the Hall effect.

Precision times four

Such measurements do in fact become possible only through the combination of the four pixel cells, because this enables disturbance variables to be excluded. It is these variables that generally complicate the task of measuring a magnetic field precisely. One source of interference is the Earth’s magnetic field, for example, which constantly changes slightly over the course of driving a vehicle from one place to another. And temperature also has an effect on measurements. If the temperature falls, a magnet’s field expands. A single sensor could incorrectly interpret this as a movement of the magnet – as a magnet that is apparently approaching the sensor. Such errors can be excluded by combining several pixel cells in a suitable manner.

With the combination of four pixel cells on one chip, the researchers have opened the door to the mass market, such as the automotive industry. For anyone looking to solder four individual sensors on to a printed circuit board, it would take a lot of time and effort to align them so precisely with each other that no measurement errors occur. This would make manufacturing time-consuming and expensive. With the new 4-pixel-cell chips, which will soon be made available for purchase by the High-Performance Center Electronic Systems, such elaborate assembly becomes obsolete.

Precision cameras measure high-quality magnets

However, the team is not only targeting the mass market, but also has sophisticated high-tech applications – such as magnetic field cameras – in its sights. Such cameras are capable of measuring the field of magnets with millimeter precision. This is important because magnets need to have very uniform magnetic fields for challenging applications such as in electric vehicles. The new 4-pixel-cell chips have the advantage that the distance between the individual pixel cells is only around a millimeter – approximately half the distance that is usual for magnetic field cameras today.

To manufacture the field of view of a large magnetic field camera, dozens of pixel-cell chips are soldered alongside each other on a printed circuit board. The smaller the distance between the chips or between the pixel cells, the higher the resolution of the camera – and the more precisely a magnet can be measured. “In industry, there have long been calls for higher resolution. With the 4-pixel-cell chip, which we have developed with an industrial partner, we’re setting new standards,” Stahl-Offergeld says.

Through the design of the new chips, the team has also made application easier. The individual 4-pixel-cell chips can be linked with each other according to the daisy chain principle. This means that not every chip has to be connected to the controller via its own cable; rather, the information in the chips can be read out successively through a single data line – that is, via a BUS system. This greatly simplifies the assembly of cameras. At present, the controller that reads out the sensor data is fitted as a separate component on the printed circuit board. In the next generation of chips, the controller unit is to be integrated into the chip. When that happens, the sensor will not just deliver magnetic field values, such as are useful for camera applications, but will directly supply the position of the magnet, which will further simplify the production of “non-click” switches and similar products.