摘要
This study presents a lightweight, flexible, and wireless patch for non-contact cardiopulmonary monitoring. The patch uses a reusable medical-grade adhesive backing that adheres to chest clothing without skin contact or disrobing, enabling quick deployment and real-time measurement of heart and respiratory signals. It is ideal for emergency or long-term care environments with limited medical resources. The sensing mechanism is based on an LC resonant circuit. An alternating excitation current generates a magnetic field B₁(t) that penetrates clothing and couples with underlying conductive tissues. This induces weak eddy currents and a return magnetic field B₂(t), forming a magnetic link modeled as a transformer and simplified into an RLC equivalent circuit. Physiological activity alters the tissue’s electrical properties, changing system impedance and resonant frequency. By tracking these shifts, cardiopulmonary signals are recorded in real time. The patch integrates the LC tank, current source, frequency counter, and wireless MCU into a flexible PCB. Its size is 9 × 5 × 0.9 cm, and its weight is 6 g, powered by a 3.7 V, 50 mAh lithium battery with 5-hour runtime. The LC circuit uses a 35 mm, 83.42 μH double-layer spiral coil and a 182 pF SMD capacitor, tuned to 1.29 MHz. A current source in the inductance-to-digital converter supplies a 1.5 mA AC current to sustain oscillation. The resonant frequency (fsensor) is measured by an internal counter with a 40 MHz clock (fref), digitized to 28-bit resolution, and transmitted to the MCU via I²C. The MCU reconstructs fsensor at a 12.5 Hz sampling rate. Data are shown on a mobile app and uploaded to the cloud for IoT-based processing. Post-processing includes polynomial detrending and bandpass filtering (0.5–3.5 Hz for heart, 0.1–0.6 Hz for respiration) to extract signals and compute vital indicators such as heart rate, respiratory rate, and cardiopulmonary coordination—all achieved via a single, contactless, wearable sensor.