High Frequency Models for the NDT Magnetic Field Sensors

The following effects of an NDT magnetic field sensor were modeled: internal impedance of the driving source, capacitive effects between coils, ohmic resistance of coils, voltage induced in coils, magnetic flux leakage between coils, nonlinear magnetic characteristic of the core including hysteresis, 3D non-uniformity of the magnetic field and eddy currents in the core. The paper presented an effective parameter extraction procedure for each effect mentioned above. The main original contribution of the paper consists in the method to model simultaneously eddy currents, hysteresis and parasitic capacitive effects which become important at high frequency in all electromagnetic devices. A SPICE nonlinear equivalent circuit of the FLUXSET sensor incorporating all these effects is proposed. The lumped circuit parameters are extracted from the field equations solution. Eddy currents are modeled by an RL chain magnetic scheme and hysteresis, which in this case prevails, is modeled by an electric inductance computed with the Chua-Stromsmoe method. For the capacitive effects, instead of the classical II approximation of a distributed RC line, based on two transverse capacitances C/2 connected at the two terminals, a more sophisticated approximation is proposed in the paper. Using SPICE simulation of the extracted circuit, good agreement with the experimental data was obtained. The proposed method is able to determine the frequency bandwidth of a newly designed FLUXSET sensor