  Electrical Capacitance Tomography (ECT) is an imaging technique providing the
distribution of permittivity in a medium by the mean of electrodes. As for any
imaging systems, the reachable spatial resolution is a key parameter. In this
paper the spatial resolution of ECT sensors is analyzed in terms of the
accuracy of an object position and of the ability to distinguish between two
close objects. Cylindrical geometry sensors are particularly studied and the
example of a square geometry sensor is used to show how to study 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 center. The best spatial resolution at the center 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.
