Properties of CMT studies by means of FEM and spice model

Abstract

A joint capacitive and magnetic tomography (CMT) is considered. Current flow in a semi-infinite 3D medium is induced by application of current between electrodes located distantly from an examined medium. These electrodes are also used to measure potential distribution at a border of the medium. Current distribution inside the medium contributes to magnetic flux measured by coils, also located distantly from the medium. A finite element model for forward problem has been developed. It is a sphere of a radius appropriately chosen. It is filled in a half with air and in a half with examined medium. Each half is described by complex conductivity. Electrodes and coils are immersed in the half containing air. A surface of the sphere is connected to ground potential. This model has been used to calculated potential distribution inside the examined medium. Aside from FE model an equivalent circuit containing resistances and capacitances, both frequency dependent and independent, has been developed and used to examine properties of the proposed technique in the frequency domain (PSpice software). It follows from the study that the potential distribution and thus the sensitivity decreases rapidly with the distance from matrix of sensors. Optimal measurement frequency for a given set of material parameters which assures the highest value of current flowing into the medium thus has been found to be dependent on all characteristic values of model. © Springer-Verlag 2007.