Accurate determination of dielectric properties for Mn-Zn toroids

This paper examines the validity of the traditional two-parallel-electrode permittivity measurement technique when it is applied to measure permittivities for Mn-Zn ferrites. A field-circuit coupled method is adopted here to carry out the examination. Intrinsic permittivities for the ferrites are assumed first. Then the permittivities, which can be measured from experiments, are calculated. Numerical results show that the measured permittivities traces the intrinsic values very well at low frequencies. As the frequencies increase, the measured values fail to reflect intrinsic permittivities. The measured permittivities for ferrites are higher than their intrinsic values. Thus, the permittivities for Mn-Zn ferrites have been overestimated. This paper will focus on studying the influence of dimensions on the measurement accuracy. By varying the inner radii of the cylindrical toroidal ferrite and keeping outer radii constant, the influence of dimensions on the permittivity measurement is studied. Results demonstrate that smaller inner radii result in higher measurement errors with the outer radius kept constant. A correction method is introduced to extract the intrinsic permittivities from their measured values.