Pulsed Eddy Current-Based Method for Electromagnetic Parameters of Ferromagnetic Materials

The least square problem between the measured and theoretical values of time-domain induced voltage in pulsed eddy current field is established to determine the conductivity and relative permeability of ferromagnetic materials. Firstly, based on the analytical expression of transient response of a semi-infinite conductor, the coupling relationship between conductivity and permeability in the early period of the induced voltage is deduced and proved. Then the method of linear fitting is used to weaken the influence of the variation of excitation magnetic field on conductivity detection results. Besides, the inversion results of permeability are corrected by using the parameters coupling relationship. Finally, the reliability of the pulsed eddy current testing method for the conductivity of ferromagnetic materials is verified by comparing with DC four-point method. And the distribution law of electromagnetic parameters for commonly used steels is preliminarily explored, which provides a pulsed eddy current testing method for evaluating the change of microstructure for ferromagnetic materials.