Influence of Capacitive Coupling on High-Fidelity Non-Contact ECG Measurement

Non-contact electrocardiogram (ECG) measurement is an advanced sensing technique that uses capacitive electrodes to detect cardiac signals through non-conductive fabrics. However, the capacitive coupling is a significant factor that affects signal-to-noise ratio (SNR) of non-contact ECG, including skin-electrode active area, material, and thickness of the non-conductive fabric. This study aims to develop a high-fidelity non-contact ECG system to evaluate the influence of capacitive coupling on ECG measurement. In this study, a polymer foam with low surface resistance (0.05 Omega/inch(2)) was designed for improving the capacitive-coupling interface between the curved body and electrode sensing surface. The system recorded excellent non-contact ECG of 29.8dB, and the accuracy of heart rate was 99.5% compared to wet-contact ECG measurement. The SNR exponentially attenuated with decreasing skin-electrode capacitance by the combined evidence of theoretical calculation and experimental results. The proposed system generates distinguishable ECG signals (SNR>0dB) at the skin-electrode capacitance above 85pF and maximum through-thickness of cotton-based cloth of 1.2mm. In conclusion, this study evaluated the influence of capacitive coupling on non-contact ECG measurements and established a lower bound of the coupling capacitance for satisfactory signal quality. Future studies may investigate whether the coupling capacitance can be further reduced.