Photographic technology visualises magnetic fields

July 23, 2014 // By Christoph Hammerschmidt
A new technique enables users to display magnetic fields as a 2D colour photography. Users can acquire, visualise and quantify the distribution of magnetic field strengths. The technique can be used to detect faulty magnetisation of semi-finished products. Experts see huge potential in quality assurance in a broad range of industries.

Sophisticated materials testing is one of the preconditions for constant output quality at the product level. In industries such as automotive, aerospace or machine tool building, magnets with customised magnetic properties and tight tolerances are increasingly used. Examples include magnetic encoders as sensors for angular and path measurement. For these components to function properly and reliably, it is necessary that they exactly maintain their stray magnetic field geometry. For this reason, quick and reliable quality checks of encoder surfaces is required.

Established measurement techniques for encoders are based on Hall sensors and inductive methods. These techniques however hit their limits when it comes to testing the 2D field strength distribution in real time. Typically, it is necessary to apply rasterisation - but this is very time consuming.

Magneto optical techniques, in contrast, can detect 2D inhomogenities of the magnetic fields as well as structure-based gradient fields, quickly and directly as an optical representation. Used in combination with a digital camera, the technology enables storing a field picture in high resolution and processing them with appropriate algorithms. Cracks, faulty magnetisation and material defects can be detected immediately. Researchers from Innovent - a non-profit research organisation based in Jena, Germany - have succeeded in generating a quantifiable image of the magnetic field out of the magneto-optical image. With this method, they can measure local field strengths. The challenge was developing the appropriate sensor layers and achieving a very exact calibration of the magneto-optical system.

The technique can be used to survey encoders, but this is not the only application; it can be used for quality control of magnetic components in general. It can be applied to characterise multipole magnetic materials, ferromagnetic steel alloys and domain materials such as iron sheets and magnetic shape memory alloys. Manufacturers, distributors and users of magnetic materials have a new measurement technique at their disposal that enables them to quickly check field strength distribution of magnetic and