Electrode–skin impedance imbalance measured in the frequency domain

Abstract

Objective:To measure the magnitude and phase imbalance of the electrode–skin interface for silver/silver chloride (Ag/AgCl) and silver (Ag) electrode pairs, highlighting the need to balance both the magnitude and phase of the electrode–skin interface. Methods:The electrode–skin impedance imbalance between two electrodes placed on ten healthy subjects was recorded over a frequency range of 1Hz–100kHz, using three electrode configurations: Ag/AgCl electrodes without skin preparation (Ag/AgClNSP), Ag/AgCl electrodes with skin preparation (Ag/AgClSP), and Ag electrodes with skin preparation (Ag-SP). A compensation network was developed to simulate impedance imbalance reduction using the experimental data. Results:The mean electrode–skin impedance imbalance at 50Hz was (37.6±47.1)kΩ and (15.0±18.3) degrees using the Ag/AgClNSP electrode configuration; (4.52±7.65)kΩ and (4.6±6.9) degrees using the Ag/AgClSP electrode configuration; and (36.2±45.1)kΩ and (3.4±3.6) degrees using the Ag-SP electrode configuration. The compensation network resulted in a mean reduction in impedance imbalance over the bioelectrical signal range (1Hz–500Hz) of 284.3kΩ and 11.9degrees; 4.6kΩ and 6.2degrees; 86.7kΩ and 2.5degrees for the Ag/AgClNSP, Ag/AgClSP and Ag-SP electrode configurations respectively. Conclusion:This study confirmed that the electrode–skin impedance imbalance can be large, and varies between subjects. Although abrasive skin preparation reduces the electrode–skin impedance imbalance, it does not guarantee a balanced electrode–skin interface, therefore, balancing the electrode–skin impedance using a compensation network has the potential to decrease bioelectrical signal interference. Significance:As bioelectrical signal interference is a function of electrode–skin impedance imbalance, to improve noise immunity of bioelectrical signal recordings, added compensatory impedance is required to balance the electrode–skin interface.