Spiral Concentric Two Electrode Sensor Fabricated by Direct Writing for Skin Impedance Measurements

In this paper, six versions of novel impedance sensors with electrodes of a form of two parallel spirals with different distances between conducting paths were elaborated. The electrodes were fabricated by direct writing technique with the use of gold polymer paste. To avoid an influence of anisotropic properties of the skin on measurements of the skin impedance, the spiral two-electrode sensors were proposed. Four resistance-capacitance-Warburg impedance models of the electrode/skin interfaces were proposed and tested. MilliQ water, KCl water solution at a concentration of 0.01 M, and human skin were used for the verification of adequacy of these models to fit the experimental data. It was stated that two of these models, A and B, have best fit to the experimental data. For measurements of skin with expected high impedance (dry skin), the sensors with the smaller distance between electrodes (version 2) should be used. Otherwise, when a patient has wet skin, which correlates with low impedance, the sensors with the larger distance between electrodes (version 7) should be applied. This is especially required when the measurements are carried out using mobile equipment, which typically has limitations related to the minimal measured impedance value.