Practical Performance Assessment of Dry Electrodes Under Skin Moisture for Wearable Long-Term Cardiac Rhythm Monitoring Systems

The use of wearable dry sensors for long term recordings of electrocardiographic bipolar leads located in comfortable areas of the body, is a requirement for detecting certain heart rhythms. Knowledge of the skin-electrode electrical performance of dry electrodes is necessary when seeking to improve various processing stages for signal quality enhancement. In this paper, methods for the assessment of skin-electrode impedance (Zse) of dry electrodes and its modelling are presented. We need to know the behavior of dry electrodes when they are moistened with skin sweat, either at the time of exercise or when it comes to warm climates, under the following posed hypothesis: the impedance magnitude of dry electrodes under study would be significantly lower after they have been moistened with sweat, and comparatively could reach levels of impedance characteristics presented by standard pre-gelled ECG electrodes. Measurements were carried out on selected dry-electrode materials such as silver, stainless steel, AgCl (dry), polyurethane and iron (Fe). These presented, |Zse| values between 500 kΩ and 1 MΩ within the main ECG frequency range (1–100 Hz), under no sweat conditions, and values of few kiloohms under artificial sweat conditions. However, in spite of the sweat conditions, open bandwidth ECG traces were of similar quality and stability, within tolerance; with dry AgCl electrode material presenting the best ECG trace performance.