An alternative method to determine the initial permeability of ferrite core using network analyzer

A simple experimental method to determine the initial complex permeability of the toroidal type ferrite core using thoroughly designed fixtures is introduced. With the ferrite core installed in a shorted coaxial line, the fixture forms a one turn coil of inductor or a shorted transmission line with distributed parameters. The relative permeability of the ferrite can then be extracted from S₁₁ of the coaxial test holder with the aid of a vector network analyzer. The "one turn coil" modeling method for radio frequencies (RF), and the transmission line modeling method for higher frequencies, are described. To improve the measurement accuracy of the test system, the subsidiary RF resistors and impedance matching circuits are integrated into the fixtures. Test results of the proposed methods achieve good agreement with the results of the traditional transmission/reflection method and the Agilent E4991A material analyzer. The influence of air gap on accuracy is discussed, as well as the upper frequency limit due to cavity resonance. Compared with some existing studies, this method achieves satisfactory accuracy and can be accomplished with normal instruments.