Abstract—Continuous monitoring of heart rate (HR) and respiratory rate (RR) plays a pivotal role in evaluating cardiopulmonary coordination (CRC). Wearable technologies have empowered long-term monitoring of cardiopulmonary parameters across a spectrum of activities, including physical exercise, mental states, dietary habits, and the effects of pharmaceutical interventions. This study presents a wearable pocket-sized cardiopulmonary sensor based on biomedical eddy current sensing technology. The novel sensor utilizes the magnetic coupling between AC coil-produced magnetic fields and cardiopulmonary eddy current-induced counteracting magnetic fields to measure resonant frequency variation in response to synchronized cardiac and lung activities without skin contact. The proposed pocket-sized sensor is characterized by its compact form with a diameter of 4.53 cm and supporting wireless data transmission. Importantly, the influence of resonant frequencies on cardiopulmonary signals was investigated through capacitor adjustments, resulting in personalized optimization of measurement conditions. In practical applications, the effect of wide fabric thicknesses on measurement performance was assessed, demonstrating identifiable signals for allowing the determination of HR and RR. In real-life scenarios, HR and RR were measured during both resting and physical exercise conditions, effectively showcasing the potential of a single compact sensor to capture essential CRC indicators. These findings provide strong validation for the novel sensor's promising potential in the realm of wearable, long-term, all-in-one cardiopulmonary healthcare.

Index Terms—Biomedical eddy current sensor, cardiopulmonary monitoring, electromagnetic induction, resonant circuit, wearable sensor.