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Pulsed Eddy Current Testing for Electromagnetic Parameters of a Spherical Conductor

This paper provides a pulsed eddy current testing method for electromagnetic parameters of a ferromagnetic spherical conductor. Firstly, the frequency domain solution of an eddy current field to the conductor is obtained by solving the electromagnetic boundary value problem. And then the time domain expression to the induced voltage across the pickup coil excited by a pulsed current in the drive coil is calculated by inverse Laplace transform based on residue theorem. Secondly, a least squares inverse problem, between the measured and analytical values of induced voltage, is established to determine the conductivity and relative permeability of the steel ball. And the coupling relationship between the two parameters of the steel ball is explored. Thirdly, the amplitude of the excitation current is changed to study the effect on the parameter inversion results caused by detection conditions. Finally, the time domain analytical formula and the parameters inversion method are verified, by comparing the theoretical induced voltage and conductivity inversion results with experimental voltage and conductivity test values by four-point method respectively.