Study on Sample Geometries for Ferrite Characterisation in the MHz Range

Abstract:
Ferrite material modelling becomes more difficult with high frequencies due to eddy current losses and dimensional resonance effects. This paper discusses the characterisation of core material properties for hysteresis and eddy current losses separately using customised thin walled ferrite samples. In a simulation study, it is shown that, with standard characterisation procedures, electric losses are incorrectly assigned to magnetic losses and vice versa for high frequencies. Further, the dimensional resonance leads to an inhomogeneous magnetic flux density over the core cross-section and complicates the correct allocation of a single large-signal magnetic flux density to specific measurement results. In an experimental test setup it is shown that for both, permeability and permittivity measurements, thin core probes show the least parasitic high-frequency effects and are thus suited best for accurate high-frequency characterisation.