Electrical capacitance tomography
Encyclopedia
Electrical capacitance tomography (ECT) is a method for determination of the dielectric permittivity
distribution in the interior of an object from external capacitance measurements. It is a close relative of electrical impedance tomography
and is proposed as a method for industrial process monitoring, although it has yet to see widespread use. Potential applications include the measurement of flow of fluids in pipes and measurement of the concentration of one fluid in another, or the distribution of a solid in a fluid.
Although capacitance sensing methods were in widespread use the idea of using capacitance measuremnet to form images is attributed to Maurice Beck and co-workers at UMIST
in the 1980s.
Although usually called tomography
, the technique differs from conventional tomographic methods, in which high resolution images are formed of slices of a material. The measurement electrodes, which are metallic plates, must be sufficiently large to give a measureable change in capacitance. This means that very few electrodes are used and eight or twelve electrodes is common. An N-electrode system can only provide N(N−1)/2 independent measurements. This means that the technique is limited to producing very low resolution images of approximate slices. However, ECT is fast, and relatively inexpensive.
Permittivity
In electromagnetism, absolute permittivity is the measure of the resistance that is encountered when forming an electric field in a medium. In other words, permittivity is a measure of how an electric field affects, and is affected by, a dielectric medium. The permittivity of a medium describes how...
distribution in the interior of an object from external capacitance measurements. It is a close relative of electrical impedance tomography
Electrical impedance tomography
Electrical impedance tomography is a medical imaging technique in which an image of the conductivity or permittivity of part of the body is inferred from surface electrical measurements. Typically, conducting electrodes are attached to the skin of the subject and small alternating currents are...
and is proposed as a method for industrial process monitoring, although it has yet to see widespread use. Potential applications include the measurement of flow of fluids in pipes and measurement of the concentration of one fluid in another, or the distribution of a solid in a fluid.
Although capacitance sensing methods were in widespread use the idea of using capacitance measuremnet to form images is attributed to Maurice Beck and co-workers at UMIST
UMIST
The University of Manchester Institute of Science and Technology was a university based in the centre of the city of Manchester in England. It specialised in technical and scientific subjects and was a major centre for research...
in the 1980s.
Although usually called tomography
Tomography
Tomography refers to imaging by sections or sectioning, through the use of any kind of penetrating wave. A device used in tomography is called a tomograph, while the image produced is a tomogram. The method is used in radiology, archaeology, biology, geophysics, oceanography, materials science,...
, the technique differs from conventional tomographic methods, in which high resolution images are formed of slices of a material. The measurement electrodes, which are metallic plates, must be sufficiently large to give a measureable change in capacitance. This means that very few electrodes are used and eight or twelve electrodes is common. An N-electrode system can only provide N(N−1)/2 independent measurements. This means that the technique is limited to producing very low resolution images of approximate slices. However, ECT is fast, and relatively inexpensive.