Electrode-skin impedance from a dielectric viewpoint.
It is well established that the frequency variation of the complex electrode-skin impedance (ESI) Z is given by Z = K(i omega)-n, where n has a typical value of about 0.8. It is not easy to find a physical reason for this behaviour. However, many materials exhibit Cole-Davidson (CD) behaviour, so that in the high-frequency (hf) region their impedance has a characteristic which is almost indistinguishable from that of the ESI. It is therefore possible that the ESI exhibits a behaviour given by the CD equation or one of its variants, but that this has not been detected because experimental measurements have not extended to sufficiently low frequencies. Whatever the ESI behaviour may be at low frequencies, there are theoretical reasons which show that Z cannot obey the above equation indefinitely as the frequency is reduced. If the deviation from it at low frequencies were found to be consistent with CD behaviour, then a physical explanation in terms of protonic fluctuations, which has previously been put forward to explain CD behaviour, would be available as a possible explanation of ESI behaviour over the whole frequency range. It is shown that any such deviation would be more likely to be detected if the variation of complex capacitance with frequency, rather than of impedance with frequency, were to be plotted.
Calderwood
J H
JH
Engineering School, Bolton Institute, UK.
D017097:Electric Impedance; D004566:Electrodes; D005712:Galvanic Skin Response / Q000502:physiology; D006801:Humans; D008954:Models, Biological; D012879:Skin Physiological Phenomena; D014054:Tomography / Q000379:methods*