Electrical Capacitance Tomography - ECT (back)

All materials possess a certain amount of electrical capacitance. This is the ability of the material to hold an electrical charge (electrical energy).

Differences in capacitance are exploited to differentiate one object from another in ECT. With sensors placed around a container, we are able to “see” the different levels of capacitance belonging to different materials within the container. The information from the sensors is fed into a computer via a data acquisition box, which processes the raw capacitance data into a live visual image for us to interpret.

On a more technical level, the sensors we use in ECT are composed of capacitance plates attached to electrodes. Typically 8-16 electrodes are used; a typical 12 electrode system can produce a live movie which refreshes at 100 frames per second.

Images produced by ECT will have a set sensitivity and resolution. This sensitivity and resolution can be altered by the size and number of electrodes that are used. Larger electrodes give better sensitivity (lower signal-to-noise ratio), whilst smaller electrodes provides better spatial resolution (but higher signal-to-noise ratio). Normally a compromise is made between the two based on the exact requirements of the situation. Recent developments are geared toward an ECT sensor design with 3D features for detecting the capacitance variations due to permittivity perturbations in the imaging volume.

Reference:
[1] Wuqiang Yang, "Design of electrical capacitance tomography sensors" Meas. Sci. Technol. 21 (2010) 042001 (13pp)
[2] Q. Marashdeh, L.-S. Fan, B. Du, and W. Warsito, “Electrical capacitance tomography - a perspective,” Ind. Eng. Chem. Res., vol. 47, pp. 3708-3719, 2008.
[3] A. Plaskowski, M.S. Beck, M. Byars, T. Dyakowski, R. He, S.J. Wang, R.C. Waterfall and W.Q. Yang, “Industrial application of electrical capacitance tomography,” Pomiary Automatyka Kontrola, vol. 42, pp. 113-115, 1996.