Method for the Measurement of Transient Magnetic AC Properties of Soft Ferrites

NiZn-ferrite materials are commonly used soft ferrites in all sorts of devices utilizing ferrimagnetic properties in a frequency range up to several tens of megahertz. Manufacturer data sheets of material properties usually contain values for the initial permeability for a given amplitude of the flux density for different frequencies, and some numbers for the loss factor. Strictly, these values are reasonable for steady-state processes with harmonic excitations only. Informations about the transient behavior of the material are contained in a single (dis)accommodation factor, if present at all. The phenomena of (dis)accommodation or generally the change of the magnetic properties with time are explained by the magnetic aftereffect (MAE). We describe a measurement system to characterize the transient magnetic properties of ferrite rings, and present some results for a commercial ferrite torus. In contrast to measurement systems working with impedance analyzers (LCR-meter) or with resonant circuits, our system gives results with a much higher time resolution. The behavior of the material can be determined almost from the very first beginning of the excitation.