Determining the magnetic permeability of ferrite steel strip by a custom inversion method

In this paper, an inverse method was developed which can, in principle, reconstruct arbitrary permeability, conductivity, thickness, and lift -o f with a multi-frequency electromagnetic method from inductance spectroscopic measurements. Both the finite element method and the Dodd and Deeds formulation are used to solve the forward problem during the inversion process. For the inverse solution, a modified Newton–Raphson method is used to adjust each set of parameters (permeability, conductivity, thickness, and lift -off) to fit inductances (measured or simulated) in a least-squared sense because of its known convergence properties. The approximate Jacobian matrix (sensitivity matrix) for each set of the parameter is obtained by the perturbation method. Results from an industrial -scale sensor are presented. The results are verified with measurements and simulations of selected case. The findings are significant because they show for the first time that the induc ta ce spectra can be inverted in practice to determine the key values (permeabilit y, conductivity, thickness, and lift -off) with a relative error of less than 5% during the thermal processing of metallic plates. M or e in fo a bo ut th is a rt ic le : ht tp :// w w w .n dt .n et /? id = 22 78 0