Multidirectional Information Fusion for Complex Defect Reconstruction Based on Induced Current Thermo-Electrical Impedance Tomography

The recently proposed induced current thermo-electrical impedance tomography (ICTEIT) is a nondestructive evaluation method for nonferromagnetic metal materials. The method reconstructs the defect profile by solving conductivity distribution from eddy currents, which has shown good performance in simple defects, but worse performance in complex defects (such as multiple adjacent defects and defects with complex contours). The main reason is that the unidirectional excitation produces low eddy current regions near the defect, which lacks reliable reconstruction information. For the problem, multidirectional excitation is able to make up for the low eddy current regions. However, previous methods simply superimpose the information of all eddy currents, and cannot integrate them for reconstruction. To solve the problem, we present a multidirectional information fusion method for defect reconstruction. The proposed method uses least squares optimization and transforms the information of multidirectional currents into a system of linear equations associated with conductivity, which constrains the solution and makes the solution satisfy each current simultaneously. Furthermore, to solve the ill-conditioning in the inverse problem, the total variation regularization method is introduced. Experiments are conducted on multiple neighboring defects and defects with complex shapes to validate the proposed method's performance.