Characterizing Dry Electrodes Impedance by Parametric Modeling for Arm Wearable Long-term Cardiac Rhythm Monitoring

There are cardiac patients requiring their ECG to be constantly monitored. The quality of long-term electrical activity feature measurements in the ECG may rely considerably on the electrodes and their long-term skin interface performance stability; thus, affecting the accuracy of clinical diagnosis and treatment. Particularly, misbehavior of the skin-electrode impedance (Zse) may cause a large degree of distortion in the ECG signal; therefore, it is important to analyze, characterize and provide a reliable modeling of any emerging dry electrode technology being used for longterm ECG monitoring. In this paper we present a useful methodology for modeling the Zse behavior. With the objective to obtain these parameters, we tested four methods for fitting curves: a) 1-time constant impedance of a circuit. b) 2-time constant impedance measurement.c) A fractional calculus with 1-time constant impedance, and d) A fractional calculus with 2-time constant impedance. As results we obtained that the 2-time constant circuit implementation of Zse using a fractional calculus proved to be best fitted to the phase plot measured with the Solartron analyzer.