Abstract: To research the computational methods about the transducer coil impedance with the magnetic and non-magnetic measured target, two computational methods, theoretic method and finite element method, are proposed. The computational model of the coil impedance is simplified as a cylindrical coil over a cylindrical measured target with the thickness δ. According to the sensor measurement principal and the electromagnetic theory, the integral expression of the coil impedance is derived, which is expanded by series in polar coordinate system in order to compute easily and feasibly. And the coil impedance value is computed by MathematicTM. Then, based on the modeling theory of finite element method, the finite element model is built. The coil impedance value and the magnetic distribution figures are obtained by finite element analysis, respectively. Finally, the results from the derivation and finite element analysis are in agreement very well by comparison, and they are given to validate the accuracy and feasibility of the derivation method with finite element method.

Key words: Eddy current sensor, Finite element method, Impedance computation, Series expansions, Transducer coil