Optimization of large scale concentric-annulus electrical capacitance tomography sensor with internal electrodes

To improve the spatial resolution of electrical capacitance tomography (ECT) images for visualizing large-scale concentric-annulus measuring area, ECT sensors with 12 external electrodes (EE) and different number of internal electrodes, 4, 6 and 8 are designed. The outer radius of the sensors is 500 mm and inter radius is 100, 150, 200, 250 mm respectively. Two excitation strategies are used, which are external-opposite-internal (EOI) and external-opposite (EO). The obtained capacitance data are used to reconstruct images using linear back projection (LBP) and Landweber iteration. Based on numerical simulation and experimental measurement, it is found that increasing the number of internal electrodes does not improve the quality of images. When LBP is used with normalized sensitivity matrix, the 12–4 internal-external-electrode (IEE) sensor with EOI excitation strategy has advantages over the EE sensor and other IEE sensors in terms of image quality and contrast. When Landweber iteration is used, the IEE sensors with EO excitation strategy can effectively eliminate the influence of abnormal capacitances. Landweber iteration can reconstruct high quality images when the sensitivity matrix is normalized according to discrete elements of measurement area, while the reconstructed images are more sensitive to the noise level.