Measurement of Magnetic Microstructures with a Faraday Rotation Magnetometer
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2020 IEEE International Instrumentation and Measurement Technology Conference (I2MTC 2020) Proceedings
A Faraday Rotation Magnetometer (FRM) is a magneto-optical setup that provides a fast and non-destructive method to measure magnetic microstructures. It is potentially particularly useful where magnetic microstructures are employed to encode information as e.g. in magnetic stripe cards or banknotes. Within this contribution, we first present a generalized setup and characterise it in order to determine the potential of the measurement principle. We define amplitude, spatial, and temporal resolution as measures for the achievable quality of a measurement. We examine the influence of the FRM?s components on the those measures. Furthermore, we discuss ways to enhance the signal w.r.t. either of the resolutions and determine their interdependence. For a specific problem, these findings may be used to decide on the suitability of an FRM as well as to choose the components and the signal enhancement steps. Subsequently, this will be exemplified by an actual industry measurement problem as well as the FRM-based solution we applied to it. Here, a setup was purpose-built for the highspeed quality assessment during the production of so-called security threads used in banknotes. Overall, an FRM shows a lot of promise for fast, non-destructive, qualitative measurements of magnetic microstructures. As of now however, quantitative measurements turn out to be very challenging and will be the focus of further investigation.