Imaging metallic samples using electrical capacitance tomography: forward modelling and reconstruction algorithms

Electrical Capacitance Tomography (ECT) is an imaging technology used to reconstruct the permittivity distribution within the sensing region.So far ECT was primarly used to image non-conductive media only.This is because if the conductivity of the imaged object is high, the capacitance measuring circuit will be almost shortened by the conductivity path and a clear image cannot be produced using the standard image reconstruction approaches.This paper tackles the problem of imaging metalic samples using conventional ECT systems by investigating the two main aspects of image reconstruction algorithms, namely the forward problem and the inverse problem.For the forward problem, two different methods to model the region of high conductivity in ECT is presented.On the other hand, for the inverse problem, three different algorithms to reconstruct the high contrast images are examined.The first two methods which are linear single step Tikhonov method and iterative Total Variation regularization method use two sets of ECT data to reconstruct the image in time difference mode.The third method, namely Level Set method, uses absulute ECT measurments and was developed using matalic forward model.The results indicate that the applications of conventional ECT systems can be extended to metal samples using the suggested algorithms and forward model, especially using level-set algorithm to find the boundary of the metal.