Key issues in designing capacitance tomography sensors

Electrical capacitance tomography (ECT) has been developed for visualising the distribution of dielectric materials using multi-electrode capacitance sensors. Although it is crucial to design an ECT sensor suitable for a specific application, some key issues have not been discussed systematically in the literature, such as the number and length of electrodes, the use of internal or external electrodes, implications of wall thickness, effects of driven guard electrodes and earthed screens (including the outer screen, axial end screens and radial screens), withstanding high temperature and high pressure, fabrication of an ECT sensor and dealing with electrostatics. This paper will address these key issues, with reference to some existing designs, and discuss the criteria for designing ECT sensors, the advantages and disadvantages of different designs, and some of the engineering challenges. Finally, some non-conventional ECT sensors, such as square, conical and 3D sensors, will be presented.