Design and Characterization of flexible Electrodes for Long-Term ECG Monitoring

Abstract

Long-term, non-invasive electrocardiogram (ECG) monitoring is essential for vulnerable populations such as neonates, pregnant women, and the elderly. Conventional Ag/AgCl gel electrodes, while clinically reliable, are limited by issues including skin irritation, signal degradation, and discomfort during prolonged use. This study presents the development of flexible, dry electrodes with  knitted conductive fabric, woven conductive fabric, and thin graphene sheets. The proposed electrode design ensures wearer comfort . The knitted fabric type provides excellent flexibility and stretchability for wearer comfort, whereas the woven type offers superior mechanical strength and durability. Graphene sheets, though mechanically weaker, significantly enhance electrical conductivity. The electrodes are fabricated on a silicone flap substrate developed using biocompatible Liquid Silicone Rubber (LSR) to ensure safe and skin-conformable application. The electrodes undergo comprehensive characterization including surface morphology and elemental composition via Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS), mechanical strength and flexibility through Universal Testing Machine (UTM) testing, and extensive electrical analysis. Electrical properties are evaluated using impedance spectrometry under both dry and wet conditions (after immersion in phosphate-buffered saline), AC conductivity measurements, voltage-frequency response, and four-probe electrical characterization. The impedance analysis reveals reduced contact resistance in wet conditions simulating skin-electrode interface, indicating improved signal conductivity. Among the developed electrodes , graphene showed the best signal quality (45.14 dB), clearly exceeding the other types including Ag/AgCl. The results demonstrate that Graphene sheets, when integrated with a biocompatible silicone substrate, combine mechanical robustness, electrical stability, and wearer comfort—delivering stable, high-fidelity ECG signals suitable for continuous, real-time cardiac monitoring applications.