Non-contact electrocardiogram measurement chair using capacitive coupling electrodes and its signal processing analysis

• The ECG measurement chair has the advantages of high signal quality and comfort. • Compared with Ag/AgCl electrode, the interval difference of ECG waves is less than 5 %. • Compared with flax and polyester, cotton material has better measurement performance. • The results suggest that the thickness of cotton fabric is less than 1 mm. This study designs an electrocardiogram (ECG) monitoring chair that achieves non-contact acquisition of ECG signals through capacitive coupling between electrodes and skin. This study uses a high impedance analog front-end (AFE) circuit to amplify and regulate weak ECG signals, with high input impedance, low voltage noise, and high common mode rejection ratio (CMRR). Signal preprocessing methods are applied to the collected ECG signals to eliminate noise, including electromyographic interference, baseline drift, and power line interference. This study compared the characteristic waveform parameters of ECG signals measured using non-contact capacitive electrodes and Ag/AgCl electrodes, such as R-wave amplitude, RR interval, PR interval, QT interval, and QRS duration. It was found that except for a significant attenuation in the amplitude of the waveform, the differences in the intervals of other characteristic waves were less than 5 %. This study simultaneously tested the influence of the material and thickness of the participants’ clothing on signal quality, and found that under the condition of 0.2 mm cotton material, a high signal-to-noise ratio (SNR) of 26.8 dB could be obtained, slightly worse than that of Ag/AgCl electrodes. In addition, this study collected ECG data from 40 subjects under different SNR conditions, and used paired t -test to evaluate whether the difference between non-contact and contact measurement was significant in heart rate variability (HRV) index. It was found that when the SNR is greater than 5 dB the p-value is greater than the significance level (0.05), indicating that there is not much difference between the two measurement results.