Skin impedance from 1 Hz to 1 MHz

The impedance of skin coated with gel but otherwise unprepared was measured from 1 Hz to 1 MHz at ten sites on the thorax, leg, and forehead of ten subjects. For a 1-cm ² area, the 1 Hz impedance varied from 10 k Omega to 1 M Omega , which suggests that the bipotential amplifier input impedance should be very high to avoid common-mode-to-differential-mode voltage conversion. The 1-MHz impedance was tightly clustered about 120 Omega . The 100-kHz impedance was about 220 Omega , which suggests that the variation in skin impedance can cause errors in two-electrode electrical impedance tomographs.