DETERMINATION OF INTERNAL STRUCTURE BY ELECTRICAL IMPEDANCE TOMOGRAPHY

Most tomographic analysis seeks to find the conductivity or another property of a domain, directly or by iteration, assuming nothing a priori about the distribution of internal features. Finite element (FE) analyses therefore require large numbers of variables, each corresponding to The conductivity etc. of one pixel or element. In 3D such analyses produce very large systems of equations Many problems of interest, such as casting or crack detection, have relatively simple internal structures. We describe recent progress with a FE algorithm in which the unknowns are parameters describing the structure of the domain, e.g. the position of material interfaces. The resulting number of degrees of freedom is thus quite small However, the FE mesh must still resolve the internal voltage field sufficiently well to detect the influence of resistivity anomalies This method, sometimes called reduction tomography, offers a good prospect of rapid imaging, suitable for on-line control, even of 3D problems, probably in a hybrid formulation with slower algorithms used to establish the initial structure. For control purposes it is speed, and the detection of change, that are likely to be more important than precision, though for problems with a sufficiently simple and well defined structure a precise image may be obtained in practice.