Inverse Problems in Electromagnetic Nondestructive Evaluation*

We present a rigorous model for electromagnetic (eddy-current) nondestructive evaluation (NDE). It consists of a pair of coupled integral equations, in which the unknowns, the electric field and conductivity of the flaw, appear multiplied together. This nonlinear (bilinear) inverse problem is solved using gradient techniques. Conclusions concerning the use of alternative algorithms, such as simulated annealing and statistical decision theory, to start and finish the inversion process are made.