Low-Cost Real-Time Fiber-Optic Distance Sensing for OPM-based Biomagnetic Measurements

Nonmagnetic polymer fiber sensors enabled real-time monitoring of OPM-MMG sensor-to-surface distance, achieving mean absolute reconstruction error of 0.0282 mm over 0–10 mm.

• Why it matters: Movement-induced changes in source-to-sensor geometry can nonlinearly affect biomagnetic signals, and nonmagnetic components are needed near optically pumped magnetometers for stable motion-artifact control.
• What they did: Polymer fiber sensors (Keyence FS-N11MN with FU-6F fibers) produced 1–5 V analog outputs sampled at 2048 Hz with 16 ms response time while a linear stage swept 0–30 mm at 50–90° incidence.
• The result: Voltage decreased nonlinearly with distance, and weighted Hill1 fits at 80–90° gave adjusted R-squared >0.9990; reconstruction error was 0.0282 mm for 0–10 mm and 0.1310 mm when calibrating 0–30 mm and evaluating 10–30 mm.