Abstract— Recent advancements in flexible patches offer stretchability and adaptability to body contours. However, most require skin contact, causing potential discomfort for long-term health monitoring. We present a non-contact electromagnetic induction-based patch sensor that integrates a passive LC tank, inductance-to-digital converter ASIC, and wireless module into a flexible substrate, characterizing compact of 9 cm × 5 cm and lightweight of 6 g. The proposed patch sensor employs biomedical eddy current sensing to establish magnetic coupling between the sensor coil's magnetic field and the counteracting magnetic fields generated by the biomedical target's eddy currents. This enables the measurement of resonance frequency variations in response to pulsatile signals across multiple physiological sites, including the heart, lungs, carotid, radial, and femoral arteries, without direct skin contact. The sensor demonstrates high applicability across various fabric materials and thicknesses, effectively detecting heart rate (HR) through fabric layers up to 5.35 mm thick when positioned at the chest. The accuracy of HR and respiratory rate (RR) Measurements across all tested physiological sites achieved mean absolute errors (MAE) within ± 5 beats per minute (bpm) and ± 3 respirations per minute (rpm), respectively. Furthermore, the sensor can effectively respond to real-time physiological state changes, as demonstrated by cold pressor test-induced HR variations and different breathing modes, highlighting its practicality in real-life scenarios. In conclusion, the proposed patch sensor provides an all-in-one flexible, non-contact solution capable of multi-site physiological monitoring, offering high accuracy, comfort, and adaptability for wearable health monitoring.

Index Terms— Biomedical eddy current sensor, cardiopulmonary monitoring, electromagnetic induction, flexible electronics, health monitoring, patch sensor, resonance circuit, wearable device.