Application of Composite Distributed Electrodes in Cardiographic Sensors

Background: An analysis of equivalent circuits used to interpret the impedance of bioelectrode for electrocardiography shows that the best description is achieved using a double-time constant model of the skin-electrode interface. However, for the measurements, it is necessary to use equipment with high input impedance, which leads to the loss of information about the real change in the bio-potential. Objective: The aim of the study is to comprehensively investigate and select the equivalent model that is used to interpret the impedance of a composite bioelectrode with distributed parameters. Methods: We used theoretical and experimental research methods. Results: It is proposed for measuring bio-potential to use Ag/AgI/Al2O3 electrodes with distributed parameters. Such electrodes are characterized by a higher contact area and their impedance is described in terms of equivalent circuits with Constant Phase Elements (CPE). It was shown that the electrode impedance is well described over a wide frequency range by an equivalent circuit typical for distributed electrodes including two CPE elements. Conclusion: It is experimentally shown that the distributed Ag/AgI/Al2O3 electrode has at least 6 times smaller polarization contribution than a commercial Ag/AgCl cardiographic electrode. It may enable more accurate measurements of bio-potentials providing less pulse shape distortion caused by polarization of electrochemical biosensors.