Frequency Mixing Magnetic Detection Setup Employing Permanent Ring Magnets.

Frequency Mixing Magnetic Detection Setup Employing Permanent Ring Magnets as a Static Offset Field Source - Pourshahidi, A.M.; Achtsnicht, S.; Offenhäusser, A.; Krause, H.-J., - Sensors 2022, 22, 8776.

In this work, a measurement head for frequency mixing magnetic detection (FMMD) is introduced which involves the utilization of two ring-shaped permanent magnets to generate a static offset magnetic field. A steel cylinder in the ring bores homogenizes the field. Through variation of the distance between the ring magnets and of the thickness of the steel cylinder, the magnitude of the magnetic field at the sample position can be adjusted. Furthermore, the measurement setup is compared to the electromagnet offset module based on measured signals and temperature behavior.

Results and Conclusions. A new measurement head was designed and constructed, incorporating ring-shaped permanent magnets for the measurement of static offset field-dependent FMMD signals /Figure 1/. The behavior of the resulting magnetic field of such an arrangement was initially studied through FEM simulations, thus confirming the expectations and serving as a guide for building the experimental setup. After characterizing this measurement head, it was compared with a standard FMMD setup incorporating an electromagnet for generating a static offset magnetic field, using active cooling and a power management cooling strategy. As expected, the analysis yielded that the PMOM setup shows an almost constant temperature during the measurement process, independent of the magnetic offset field. Furthermore, a comparison was performed between the pulsed-EMOM and PMOM by measuring an immobilized magnetic nanoparticle sample of Synomag D 70 nm. The variation among signals was determined to be 4.5% which is in an acceptable range. Moreover, utilizing the measurement signal f1 + f2 (f1 - high frequency of the driving field and f2 - low frequency of the exitation field) at a specific magnetic offset field, where the maxima are occurring, yields a 60% higher signal, and therefore provides an advantage in measuring lower concentrations than using the typical f1 + 2·f2 harmonics without an offset field. This feature could be applied for future FMMD sensitivity enhancement. However, one has to consider the limitations of the current module as well. The PMOM is bulkier than the standard handheld device. Further developments are required to automatize the measurement procedure and to enhance the user-friendliness and portability of the device for in-field applications.

FIGURE 1. (Left) Schematic block diagram of the excitation and readout circuitry connected to the cross-sectional view of the measurement head assembly. (Right) Photo of the internal configuration of the measurement head and the high- and low-frequency excitation coils around the detection coils. The sample is inserted into the measurement head from above, and a light sensor is used to monitor the insertion and removal of the sample.

Publication: Pourshahidi, A.M.; Achtsnicht, S.; Offenhäusser, A.; Krause, H.-J. Frequency Mixing Magnetic Detection Setup Employing Permanent Ring Magnets as a Static Offset Field Source. Sensors 2022, 22, 8776.



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Last Modified: 21.12.2022