MEMS Variable Reluctance Sensor Based on a Micromachined Coil

Nasr, D;Bau, Marco;Nastro, A;Bertelli, S;Ferrari, V;et.al.
(2025) AISEM Annual Conference on Sensors and Microsystems

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Abstract
This work explores the potential of using a MEMS micromachined coil combined with an external magnet and front-end electronics as a variable-reluctance (VR) microsensor. The development of VR microsensors using MEMS technology represents a significant advance, as it could enable high spatial resolution for focused detection of small metallic/ferromagnetic target components and parts. To validate the principle, a squared micromachined coil with a side length of 2180 μm was adopted to detect the rotation of a ferromagnetic drill bit within the magnetic field generated by a neodymium magnet. The temporal variation of the associated flux due to the reluctance change induces a voltage in the micromachined coil that can be correlated with the target rotation speed. The VR microsensor signal was compared with a reference signal from an optical sensor used to monitor the drill bit rotation. Rotation speeds of up to 1551 and 1393 rpm were detected for drill bits with diameters of 5 and 8 mm, respectively, at a stand-off distance from the micromachined coil of approximately 2 mm, validating the proposed approach.
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Nasr, D., Bau, M., Nastro, A., Bertelli, S., Ferrari, M., Said, M. H., Flandre, D., Mansour, M., Tounsi, F., & Ferrari, V. (2025). MEMS Variable Reluctance Sensor Based on a Micromachined Coil. Sensors and Microsystems. AISEM 2025. Lecture Notes in Electrical Engineering, p. 164-169. https://doi.org/10.1007/978-3-032-08271-8_26