A new method to characterize the soft magnetic material

Current developments in the field of power electronic devices are leading to miniaturization. However, if storage inductors or small transformer are needed, the final dimension of a device is determined by these components. A size reduction is usually possible by increasing the operating frequency and the initial permeability, if ferrite with high magnetic performances is available. The ferrites producers and user are more and more interested in quickly and complex characterization of the ferrite cores. To obtain the characteristics of soft ferrites operating in the domain of the high frequency and having low hysteresis and power losses a new and complete experimental set-up was designed and used. Many papers report the dependence of the magnetization processes in soft ferrite cores on excitation frequency [1], [2]. Especially the microstructure, the resistivity and the permittivity could influence the distortion in the RL circuits with MnZn or Ni-Zn ferrite cores [3]. In some ferrites the pores and impurities can impede the movement of domain walls and the coherent rotations leading in magnetization processes. In this case the magnetization processes will be influenced by the frequency above the resonance ferrimagnetic frequency [4]. In ferrites with low porosity in static process or at low frequency the movement of domain walls will lead the magnetization process [5]. At high frequencies the wall can't fallow the field and the movements of the wall are irreversible due to the damping [6]. By using the Fourier techniques for the spectral analysis we have studied the digitized output signal in a secondary coil of a transformer with a Ni-Zn-Cu ferrite core. The cores were samples with different microstructure sintered at various temperatures [7]. The differences observed between the spectral coefficients at various excitation frequencies is discussed in relation with the two main magnetization processes. The behaviour is related to the microstructure and to the experimental hysteresis loops of the samples. In the same time different waveforms for the magnetic field strength were used to obtain minor and major hysteresis loops.