A new procedure for reconstructing the aged regions of the ferromagnetic bodies Ioan Florea Hantila and Cleante Petre Mihai Politehnica University of Bucharest, Bucharest, Romania Costin Ifrim Ecoair Corp., Hamden, Connecticut, USA, and Teodor Leuca University of Oradea, Oradea, Romania Abstract Purpose – This paper presents an efficient procedure for reconstructing the aged region of ferromagnetic material. Design/methodology/approach – The aging of the ferromagnetic material leads to changes of B -H relationship. This property may be used for detection of the degraded parts of ferromagnetic pieces. In numerical procedures the region with a possible aged zone is described by a finite number of subdomains where the flaw vector is defined with binary entries. Findings – Because of the small B -H changes, the magnetic field modifications linearly depend (matrix T) by the flaw vectors. Using a double Gauss pivotation scheme, an enough well conditioned and invertible submatrix is extracted from the matrix T. The unknowns associated with this submatrix (called main unknowns) can be easily obtained by a linear relationship from the rest of the unknowns (called minor). In the set of the minor unknowns we search for that vector which gives the smallest error of the principal unknowns in comparison with the values 0 or 1. Originality/value – This procedure leads to a spectacular increasing of the efficiency in comparison with the known procedures. Keywords Magnetism, Ageing (materials) Paper type Research paper 1. Introduction The problem of flaw reconstruction is an ill-conditioned inverse problem that needs a huge number of direct problem solutions. If the flaw is a crack, then the vanishing of the conductivity leads to an important modification of current density distribution. The eddy current testing seems to be the best procedure for crack reconstruction (Pavo and Miya, 1994). For deep crack, the investigation techniques need a low working frequence or a periodic excitation in order to obtain a suitable depth penetration (Chady et al., 2000; Preda et al., 2002). Trying a lot of flaw shapes, it will be validate which will give the smallest difference from calculate and measured magnetic field. If the damaged zone is descibed by n subdomains, then we need 2 n field computations. This huge effort may be decreased by using of neural networks (Chady et al., 2000) or genetic algorithms (Arkadan et al., 1994). The aging of the ferromagnetic material, which may be caused by mechanical stress, does not modify the conductivity but leads to changes of B -H relationship. This property may be used for detection of the degraded regions (Miya, 2002; The Emerald Research Register for this journal is available at The current issue and full text archive of this journal is available at www.emeraldinsight.com/researchregister www.emeraldinsight.com/0332-1649.htm COMPEL 24,2 620 COMPEL: The International Journal for Computation and Mathematics in Electrical and Electronic Engineering Vol. 24 No. 2, 2005 pp. 620-627 q Emerald Group Publishing Limited 0332-1649 DOI 10.1108/03321640510586222