MEASUREMENT OF THE TIME-DEPENDENCE OF THE COMPLEX MAGNETIC PERMEABILITY OF SOFT-FERRITES
Paul Fulmek – Hannes Wegleiter – Peter Haumer – Bernhard Schweighofer
Ferrimagnetic devices in electrical engineering are usually described by a single complex figure of permeability, which allows deducing simple, but very practical expressions for the inductance in AC considerations. This effective permeability value, however, is dependent on the amplitude of the AC excitation, on the DC magnetic state of the material, and on temperature. Furthermore, it changes considerably with time after the excitation has been applied (magnetic viscosity, magnetic after-effect). In principle, standard measurement systems (impedance/material/network-analyser, LCR-meter) operate under steady-state conditions, after certain settling times have passed. In this paper we describe our measurement system, which is able to characterise the settling process itself, as well. The achieved effective time resolution for the measured impedance values is in the range of 50 kHz. This
system is used to characterise the time-dependent, transient magnetic properties of ferrite samples. Results are presented for a commercial NiZn ferrite torus.
Keywords: ferrimagnetic materials, magnetic permeability, magnetic variables measurement, soft magnetic materials, transient magnetic properties, after-effect