An electrical capacitance tomography sensor with internal-external electrodes

Using a conventional electrical capacitance tomography (ECT) sensor, it is difficult to image either small objects or objects in the central area. For the measurement of a thin layer of solids found near the walls of a circulating fluidised bed (CFB), a new type of sensor is proposed, having conventional external array of electrodes plus an additional internal array of electrodes. Sensitivity maps for this sensor were generated using a finite difference method (FDM) and its performance in image reconstruction evaluated using both a linear back-projection (LBP) and an iterative algorithm. Compared with a square external-electrode sensor, the new sensor has higher sensitivity in the central area of the sensor, and thus is able to produce improved images. This has significant advantages for imaging the well-known core-annulus structure of solids distribution in CFB combustors.