3D effect of electrical capacitance and resistance tomography sensors

In electrical resistance tomography (ERT) sensors, small pin electrodes are commonly used. It is well known that the pin electrodes cause severe field distortions or 3D effect, and the sensing region of such an ERT sensor is not constrained to the pin electrode plane, but spreads to a large volume. This is also true for electrical capacitance tomography (ECT) sensors, even though it is less severe because of larger size electrodes in ECT sensors. However, when the length of electrodes in an ECT sensor is reduced to almost the same dimension as those in ERT sensor, the 3D effect may be equally obvious. To investigate the 3D effect of ERT and ECT sensors, simulation was carried out with different lengths of electrodes and the results are compared with the corresponding 2D simulation. It is concluded that sensors with longer electrodes usually have less 3D effect without guard electrodes. To investigate the effectiveness of grounded guards, 3D simulation was carried out for ECT sensors with grounded guards and the results are compared with the previous results in term of the 3D effect. It is found that the 3D effects of ECT and ERT sensors without guards are similar to each other, and the grounded guards can reduce the 3D effect of ECT sensors to a great extent.