Year: 2026
Type: preprint
Abstract: Background Accurate tracking of the distance between magnetic sensors and biological tissue is particularly relevant to biomagnetic measurements in which stable wearable sensor configurations are not feasible, such as optically pumped magnetometer-based magnetomyography (OPM-MMG), where movement-induced changes in source-to-sensor geometry can nonlinearly affect the recorded signal and complicate motion-artifact control. In OPM setups, such measurements must be performed with strictly nonmagnetic components to avoid noise interference. Therefore, a nonmagnetic, ideally compact approach is needed for real-time monitoring of the sensor-to-source distance. Method Low-cost, non-magnetic, thin polymer fiber sensors (Keyence FS-N11MN with FU-6F fibers) were evaluated for accurate real-time distance measurement at sub-mm resolution using a fully automated linear stage across a 0–30 mm range and controlled incidence angles between 50° and 90°. The sensors generated analog voltages from 1 V to 5 V, sampled at 2048 Hz, with a 16 ms response time. Custom scripts were used for data analysis, including averaging, noise estimation, and uncertainty weighting. Results Voltage decreased nonlinearly with distance. For pooled 80°–90° data, weighted Hill1 fits over 0–10 mm and 0–30 mm each yielded an adjusted R 2 greater than 0.9990. Across the five sensors, the mean absolute reconstruction error was 0.0282 mm for 0–10 mm calibration and evaluation and 0.1310 mm when 0–30 mm calibration was evaluated over 10 – 30 mm. A periodic modulation was observed beyond 10 mm, independent of cross-talk, and was consistent with the sensor’s discrete internal signal levels. Conclusion Low-cost, nonmagnetic polymer fiber sensing may provide a compact, real-time approach for monitoring sensor-to-surface distance over 0–10 mm in OPM-based biomagnetic measurements; extension across the full 0–30 mm range will require range-specific calibration and further validation on skin-facing surfaces.
Authors: Marco Hübner, Justus Marquetand, Haodi Yang
Language: English
Subfield: Atomic and Molecular Physics, and Optics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W7224110048