Electrode-Skin Impedance Component Estimation in the Time-Domain

This paper presents a method to estimate the individual component values of a bipolar electrode-skin interface, with future intent of applying compensatory electrode-skin impedance balancing prior recording bio-signals with electromyography. The electrode-skin interface was stimulated by a step input and the output behaviour was characterised using a single exponential model per electrode. The method was applied to simulated circuitry, passive component circuitry and a human subject. The accuracy of the method was determined using the known values that comprised the simulated and passive component circuitry. Nine of ten simulated data sets resulted in accurate estimations, with a maximum error of 0.763% and a mean error of 0.076% per component. The method also produced successful estimates for nine of the ten physical circuitry data sets, with a maximum error of 10.2% and a mean error of 3.49% per component. The method was unsuccessful in estimating the individual electrode-skin impedance components for the human subject: this was due to the system failing to reach steady state during the stimulation period. The authors suspect a DC offset caused by the half-cell potentials associated with the electrode-skin interface were the cause of the unexpected behaviour.