Characterization of dielectric and magnetic properties of Mn-Zn ferrites by using two capacitors made up of solid cylindrical samples with different dimensions

Mn-Za ferrite materials present both high permittivity and high permeability within kHz - MHz frequency range. This makes experimental measurement of their intrinsic permittivity and permeability inaccurate. This paper introduces a new method to accurately extract intrinsic permittivity and permeability simultaneously. The method, which is based on Newton-Raphson iteration, uses solely the measured permittivity from two capacitors made up of flat solid cylindrical ferrite samples with different dimensions, and requires no information of complex permeability. It is shown in the paper that this Newton-Raphson based iteration method is accurate and robust in tracing the intrinsic complex permittivity and permeability for Mn-Zn ferrites, irrespective of the initial estimations for iterations.

I. Introduction

Ferrimagnetic cores find widespread applications in power electronic devices and EMI suppression within kHz through MHz frequency range [1], [2]. The relative permittivity of some Mn-Zn ferrites is as high as at several hundred kilohertz [3]. The relative permeability of most Mn-Zn ferrites can easily exceed several thousand and is continuously being increased to meet the device miniaturization requirement. Higher permittivity and permeability imply shorter wavelength. The dimensions of practical Mn-Zn ferrite samples used to measure complex permittivity may become comparable with the wavelength at the frequencies of interest. Thus, the validity of conventional methods used to characterize Mn-Zn ferrites need to be examined.