Wide-Range Low-Power Low-Voltage Integrated Capacitance-to-Digital Converter for On-Body Sweat-Rate Sensing

This article presents the experimental evaluation of an integrated capacitance-to-digital converter (CDC) paired with a custom capacitive sensor fabricated on a flexible printed circuit board (FPCB) for continuous on-body sweat-rate monitoring. The system utilizes a syringe pump setup to simulate controlled sweat production, enabling precise calibration and validation under realistic flow conditions. Electrical characterization demonstrates high linearity, stability, and low relative error across a wide capacitance range (60 fF–880 pF), even at low supply voltages (0.9 V), supporting its suitability for energy-efficient wearable applications. The CDC achieves low power consumption of $2.1~\mu $ W and a wide full-scale range, enabling accurate detection of capacitance changes corresponding to variable sweat rates. Despite minor noise effects from RF interference and fluid friction in the microfluidic channel, the system demonstrates significant potential for miniaturization, flexibility, and reliable sweat-rate monitoring. These results highlight the feasibility of real-time physiological monitoring in wearable healthcare devices.