Parallel High Capacitance Capacitors Connected With Flexible Electrodes for Enhancement of cECG Signal Quality

In the application for sleeping cardiac monitoring utilizing capacitive electrocardiogram (cECG), a raw cECG signal with high-fidelity is typically difficult to be obtained due to the low coupling capacitance made up of human skin, low dielectric fabrics, and sensing electrodes. In order to overcome this challenge, this study proposed a parallel capacitor-flexible electrode for enhancing the performance of an electrocardiogram (ECG) monitoring system, and it investigated the influence of parallel capacitors on ECG monitoring. Parallel capacitors at both ends of the coupling capacitance could increase the coupling capacitance and reduce the equivalent impedance, which could improve the signal-to-noise ratio (SNR) (from about 10 dB to more than 30 dB) of the acquired cECG signals. In this study, first, the optimal connection point and parallel capacitor were determined; second, the application of the proposed system was demonstrated, and well-characterized cECG signals (SNR 35.066 dB) were obtained. The cECG signals acquired by the proposed reference system were in good agreement. The calculated intervals of all subjects extracted from the cECG signals were within the standard interval ranges, which was consistent with the health condition of the subjects. The results also showed that the proposed system had an average HR error of 1.4% for 20 min compared to the reference system. In conclusion, this study innovatively proposed a method to enhance cECG signal quality, which has a promising potential for long-term sleeping ECG monitoring.