On the Difficulties to Determine the Intrinsic Material Parameters for MnZn Ferrites

This paper investigates the difficulties of obtaining intrinsic material parameters, permeability, conductivity, and permittivity of MnZn ferrites for the frequency range that is relevant for radiated EMI simulations, up to 300 MHz. Due to the high relative permeability (e.g., 3000 at 1 MHz) and high relative permittivity (e.g., 50000 at 1 MHz) combined with significant DC conductivity it is difficult to obtain intrinsic material parameters needed for electromagnetic full wave simulations. Further, the complexity increases with increasing frequency (e.g., 5 MHz) due to negative apparent permeability. Skin effect and dimensional resonances within the test objects cause a violation of the basic assumptions that are used to extract material parameters from a sample, since the parameters retrieved depend on the size and shape of the test samples. Carefully conducted experiments further showed that the material shows non-reciprocal behavior without DC magnetization and the possibility that the magnetic flux not only depends on the magnetic field, but also on the electric field, suggesting the possibility of bi-anisotropic behavior.