Microwave characterization of ferrite particles

Several different mixture equations have previously been used to characterize the microwave properties of the ferrite particle-insulating medium mixtures. For very low particle concentrations, these equations give nearly the same results. But when the particle concentration is higher than a few per cent, these equations generally give different results. Based on microwave measurements and numerical calculations, the validity of five well-known mixture equations has been examined in this paper. The experimental results show that both the Bruggeman and QCA-CP ('quasi-crystalline approximation with coherent potential') equations can accurately describe the microwave properties of the ferrite-medium mixtures, and that the Lichtenecker, Logarithm and Maxwell-Garnett equations are not suitable for characterizing the ferrite-medium mixtures over a wide particle concentration range at microwave frequencies. The microwave intrinsic permeability and permittivity spectra of some BaZn2-xCoxFe16O27, Ba4Zn2-xCoxFe36O60 and Ba2Zn2-xCoxFe12O22 ferrite particles have been presented, which were calculated from the measurement data of the ferrite-wax mixtures using the Bruggeman equation. The microwave properties of these ferrite particles have also been discussed. In the 1-6 GHz range, both the real and imaginary parts of permeability of BaZn2-xCoxFe16O27 and Ba4Zn2-xCoxFe36O60 ferrite particles evidently increase with the increasing Co concentration. Both the real and imaginary parts of permittivity of Ba2Zn2-xCoxFe12O22 ferrite particles apparently decrease as the Co concentration increases.