Physical limitations on spatial resolution in electrical capacitance tomography

Electrical capacitance tomography (ECT) is an imaging technique providing the distribution of permittivity in a medium by means of electrodes. As for any imaging systems, the accessible spatial resolution is a key parameter. In this paper the physical limitations on the spatial resolution of ECT sensors are analysed in terms of the accuracy of an object's position and of the ability to distinguish between two close objects for any sensor geometry. Cylindrical geometry sensors are particularly studied and the example of a square geometry sensor is used to show how to apply the calculations to any other geometries. In cylindrical geometries, it is shown that a 50% gap between electrodes is a good compromise and that increasing the number of electrodes improves the spatial resolution near the electrodes but decreases the spatial resolution in the centre. The best spatial resolution at the centre of the sensor is obtained with 3 or 4 electrodes. In the square geometry studied, it is shown that a better distribution of the spatial resolution is obtained when there are electrodes in the corners.

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