Fully Integrated Flexible Electromagnetic Induction-Based Patch for Noncontact Health Monitoring

Recent advancements in flexible patches offer stretchability and adaptability to body contours. However, most of them require skin contact, causing potential discomfort for long-term health monitoring. We present a noncontact electromagnetic induction-based patch sensor that integrates a passive inductance-capacitance (LC) tank, inductance-to-digital converter application-specific integrated circuit (ASIC), and wireless module into a flexible substrate, characterizing compact of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$9\times 5$ </tex-math></inline-formula> 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 (MAEs) 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 (CPT)-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, noncontact solution capable of multisite physiological monitoring, offering high accuracy, comfort, and adaptability for wearable health monitoring.