Field analysis and electrical models of multi-electrode impedance sensors

Two types of multi-electrode sensors (with conducting and insulating walls), used in the impedance tomography systems, have been considered theoretically using finite element analysis (FEA). The distribution of potentials and current densities (field analysis) has been studied, assuming that sensors were supplied from current source. Potential differences between the adjacent electrodes and between electrodes and conducting wall, for sensors with insulating or conducting wall, respectively, were determined as a function of distance of measuring electrodes from supplying ones. Analysis of the influence of inhomogeneity location, for both types of the sensors, on measured potential differences has been carried out. On the basis of FEA results, semi-distributed, and then lumped parameter models of the sensors have been proposed. Character of variations of measured potential differences, caused by an inhomogeneity, is intelligible very well in terms of the derived models. Furthermore, the models allow estimation of the influence of frequency of measuring signal on the measured potential differences. Results of the theoretical analysis have been evaluated experimentally and a good agreement between theory and experiment has been obtained.