Analyzing the Effect of an Externally Applied Force on the Electrode-Skin Impedance

In this study, the impact of force on electrode-skin impedance is examined; electrode-skin impedance can impact the quality of the recorded biological signals. Surface biopotential electrodes experience different levels of applied force during biological signal measurements, especially with wearable biomedical sensor systems. The analysis was based on applying different force levels (0 N, 8.9 N and 22.2 N) on different types of surface biopotential electrodes: 1) Ag/AgC1 electrodes, 2) Stainless steel electrodes, 3) Orbital electrodes and on determining the effect of removing the applied force from the electrodes sites on electrode-skin impedance. Electrode-skin impedance was sharply decreased when the first force level was applied on dry electrodes and in the absence of electrolyte gel in the case of Ag/AgC1 electrodes. Applying electrolyte gel to Ag/AgC1 electrodes made inconsistent results among the subjects under high force level. Performing skin preparation caused the electrode-skin impedance to be sensitive to repeated application of loading/unloading of fixed low force level (5 N). The hysteresis effect was experienced in most of the measurements when force was removed from electrodes sites. An electrical circuit (RC) was used to model the electrode-skin interface. Increasing the applied force level on the electrodes sites resulted in an increase in capacitance (Cd) values and a decrease in resistance (Rd and R S) values of the electrical circuit model components for the electrode-skin interface.;Decreasing the electrode-skin impedance by the force technique would be beneficial for improving the biological signal quality and improving the performance of modern wearable physiological monitoring system.