Imaging irregular structures using electrical capacitance tomography

Abstract

Electrical capacitance tomography (ECT) is widely used in research for different applications, e.g. in the petroleum, pharmaceutical and power industries, due to its nonintrusive and noninvasive features and low cost. So far, ECT has been successfully used with regular structures, such as circular and square shapes. However, in some cases, the measurement electrodes cannot be mounted directly on an irregular structure, high temperature objects or corrosive objects. In this work, a method is proposed for ECT to be used with an irregular structure, by filling the gap between the irregular structure and a regular ECT sensor wall. Accordingly, a split matrix method is proposed for image reconstruction. The characteristics of sensitivity maps with the filling method and different structures are investigated. To calculate sensitivity maps, two methods are used: the perturbation method and the potential method, and their effects on image quality are compared. The results show that there is no obvious difference between these two methods for imaging construction, but the potential method is more efficient than the perturbation method. Among different shapes, an image of a triangular object has a large deformation due to its sharp angle and hence the filling method is not suitable for imaging a triangular object. The split matrix method modified by relaxation factors is suitable for irregular structures in general and can generate satisfactory images. A hardware system based on an impedance analyser and a software package have been developed and used to validate the proposed methods. The experimental results show that the proposed method is promising for imaging two-phase flows in irregular structures.