Paul Wilcox, Alexander Velichko and I have now extended the TFM/FMC in various directions. The overall idea of the current work is to try and extract as much information about the interior of a structure as possible. This all stems from the idea that in measuring the ultrasonic response, what we are actually doing is extracting information from a scattering matrix. At a fundamental level, this is the available information: nothing more, nothing less. Given this limit on the nature of the available information the question is what is possible? For example, one approach is to compute many forward models of all possible wave-defect interactions and to store this information in a large database. The defect characterisation challenge then becomes one of finding closest match between a measurement and the database. For those intersted in exploring these ideas in more detail book is now available.
Bruce Drinkwater 