The mosaic electrical characteristics of the skin

The authors constructed a suction microelectrode with a 200- mu m internal diameter and performed several tests on two male subjects. It was found that the average skin impedance on the forearm was larger than the average impedance on the palm and that the ratio between the maximal and minimal skin impedance was larger for the forearm than for the palm. For both the magnitude and variance of skin impedance decreased with increasing stimulus frequency. The density of low-impedance points observed on the forearm and palm was consistent with the density of DC current pathways through the skin as indicated by traces left on 1-cm ² Ag electrodes. The ratio between the highest and lowest impedances decreased as temperature decreased. The authors were not able to break down the skin using the suction microelectrode. Tests suggest that breakdown is of thermal nature, and that the thermal capacitance of the saline in the suction microelectrode prevents the temperature of the underlying skin from increasing very rapidly, increasing the breakdown voltage.