Magnetic Field Analysis for Dimensional Resonance in Mn–Zn Ferrite Toroidal Core and Comparison With Permeability Measurement

This paper studies the calculation method of core loss and magnetic state in Mn-Zn ferrites under an arbitrary waveform excitation. The effective dielectric constant, which is caused by a thin high-resistive layer at the grain boundary, is treated as a modification of Ohm's law by using an equivalent circuit. This procedure enables us to calculate both the dimensional resonance and eddy-current loss. To confirm the accuracy of the proposed model, the size dependence of the complex permeability and core loss of the toroidal core is analyzed. These results show a good agreement with the experimental measurement in the megahertz region. By using the same model, the core loss mechanism excited by a triangular-wave current is analyzed. In the low-frequency region, the core loss is suppressed by the reduction of a steep change in magnetic flux. However, the core loss near the resonant frequency is increased at the turning point of the current wave, where the time derivative of the current changes discontinuously and a higher harmonic component is induced.