Faraday Magnetometer

In addition to the conventional methods of magnetic field measurement, there are other physical effects which allow to spatially resolved image a magnetic field, which are rarely instrumentalized for measurement purpose. One of them is the Faraday effect. After a brief description of the Faraday effect, a polyethylene foil with a partial magnetic colour coating is described, which has to be measured for quality statements during production. This coating is provided with a periodic pattern and partially also has microstructures in the sub millimetre range, which has to be resolved laterally with the measuring instrument at a production speed of 3 m/s. It is shown with a presented line sensor, which has a pixel area of 63.5 µm x 63.5 µm, that this resolution, in the row direction and in the direction of the polyethylene foil, with a 1:1 imaging optics, is achieved. After digitizing at a 63.378 kHz line scan rate, with 64 pixels per line, the measurement data are cached in a 32 kB FIFO memory where they are read from a Raspberry Pi. The Raspberry Pi streams the measurement data, after minimal signal processing, to an external hard drive, where it is then available for offline analysis. For the proof of functionality, a magnetic field measurement of a coated polyethylene foil in the production was carried out on a trial basis and the results are briefly discussed. It is shown that the microstructures can also be resolved by the measuring instrument at full line speed and based on these values, a qualitative statement about the coating can be made and therefore also provides empirical data for a signal processing development.