摘要
This study demonstrates a flexible capacitive humidity and respiratory sensor achieved by integrating graphene as a sensing electrode with a polyimide-based flexible printed circuit board (FPCB). The sensing principle is governed by rapid surface adsorption and interfacial polarization, where moisture interaction effectively modulates the composite dielectric permittivity within the high-intensity electric field of the parallel-plate sensor. A dedicated CMOS readout circuit is implemented to suppress parasitic capacitance effects, thereby facilitating high-sensitivity signal acquisition. A wet-transfer process is implemented to integrate graphene onto the FPCB substrate. For relative humidity (RH) sensing, the proposed sensor exhibits a sensitivity of 8.6 fF/%RH at $25 similar to<^>{\circ }$ C, with a 2.25-fold increase in capacitance as RH varies from 40%RH to 90%RH while achieving a humidity resolution of 0.12%RH. For respiratory monitoring, the sensor demonstrates a flow-rate sensitivity of 0.5 mV/liters per minute (LPM) for nasal exhalation, with a flow-rate resolution of 0.69 LPM. The rapid subsecond response of the capacitive sensing mechanism enables real-time breathing detection. The proposed graphene-based flexible sensor, combined with the CMOS readout circuit, provides a compact solution suitable for wearable and continuous respiratory monitoring applications.