An original new method to better characterize ferrite materials used in power electronic applications

Abstract
Today, linear properties of high frequency magnetic cores used in power electronics are exclusively stated by unique complex permeability, and the measurement of this variable is based on a magnetostatic approach. In MnZn ferrite cores, the grain insulation, which avoids the circulation of induced currents at low frequency, goes out of efficiency beyond about ten or a hundred kHz. Since eddy currents are able to circulate in these materials, by conduction or displacement of charges, usual reasoning is no more credible. A description closer to reality must also take complex permittivity into account. The purpose of this article is first to justify that both complex permeability and complex permittivity are necessary to accurately characterize ferrite materials, especially when frequency is growing up. The analytical model used to deduce these physical values is presented, and its validity domain is discussed. Experimental results are presented with this aim.