Real time impedance plots with arbitrary frequency components

Temporal changes in the impedance spectra of bioelectrodes in contact with skin provide useful data for comparisons between differing electrode materials and skin preparation methods. Traditional impedance measuring systems employ swept frequency methods which will distort results in the impedance spectra of a sample which has nonstationary electrical characteristics. The system reported here obtains impedance spectra by applying a digitally constructed waveform consisting of many frequency components. This allows impedance values to be measured at a number of frequencies simultaneously. Sample data are provided and compared with data obtained using similar square wave techniques.