Requirement-Adapted Enhancement of a Faraday Rotation Magnetometer’s Output

Abstract

Magnetic microstructures are a useful tool to encode information. In order to repeatedly make use of this information a non-destructive measurement system is needed. Such a system would be applicable to many technical problems, however, within this contribution we discuss a method to analyse the magnetic pattern of the security thread used in banknotes specifically. In order to assess the quality of the threads’ magnetic patterns during their production, a previous study used a Faraday Rotation Magnetometer (FRM). An FRM is a magneto-optical – and therefore non-destructive and non-contacting – setup based on the Faraday effect, which correlates the strength of a magnetic field with the rotation of polarised light. Albeit meeting the required specifications, this FRM’s amplitude resolution wasn’t sufficient to allow meaningful quantitative measurements. Hence, within this contribution we discuss the suitability and scope of an FRM for quantitative measurements of magnetic microstructures. We present a generalised version of the previous FRM and characterise it with regard to its amplitude, spatial, and temporal resolution. We point out ways to enhance the signal and show the limitations of such measures separately as well as comprehensively. From this we derive a way to estimate the feasibility of an FRM as a quantitative measurement device for a given set of parameters. Furthermore, this contribution may be used as a build and signal enhancement guideline for a similar setup.