Frequency analysis of electrical impedance tomography system

An equivalent four-terminal model of an impedance tomography sensor in the measuring channel is presented. The frequency dependence of the potential difference measured between voltage electrodes of the sensor is analyzed theoretically and compared with the results of experiments carried out in the range 10 Hz-20 kHz. A good agreement is found. Results of the analysis revealed the frequency range of the measuring signal (10 Hz-5 kHz in the considered case) for which the potential difference is constant or varies insignificantly. At higher frequencies (more than 5 kHz), however, an evident variability was found-the higher the frequency, the higher potential difference. This results from the impedance characteristic of the tomography system including interfacial layer impedances, parasitic capacitances (particularly between the electrodes of the sensor) as well as signal source and voltmeter parameters. Analysis of the frequency characteristic of any individual tomography system is suggested to select the appropriate frequency of measuring signal and hence to avoid variability in the measured potential difference.