Ba2Co2Fe12O22 – ZnFe2O4 ferrite composite having equivalent permeability and permittivity for ultra-high frequency band antenna applications

Abstract

In recent decades there is a rise in the use of communication devices operating at ultra-high frequency. The antenna is an important component require in these devices. For high frequency application, antenna size must be miniaturized and the use of magneto-dielectric ferrite materials can effectively reduce the size of an antenna (Harris VG, 2012), as they have both magnetic and dielectric properties. Ferrite materials have advantages of high refractive index (n=√(µ'ε')), which is essential for miniaturization and good impedance (Z=Zo√(µ'/ε') ) matching between substrate and free space. ZnFe2O4 (ZnF) and Ba2Co2Fe12O22 (Co2Y) ferrites are important spinel and hexagonal ferrites respectively (Smit & Wijn, 1959). Hexagonal ferrites have higher dispersion frequency and good magnetic properties above 200 MHz. In this study, composites between Co2Y and ZnF were synthesized with the composition (Co2Y)1-x(ZnF)x; (x= 0.0, 0.25, 0.50, 0.75 and 1.0) through co-precipitation route. Co-precipitated powder was calcined at 1000oC to get composite ferrite powder. Pellets and toroids were fabricated using composite powder and specimens were sintered at 1100oC for 4 h. Phase and structural analysis was carried out using X-ray diffraction (XRD). Fig. 1 shows the XRD pattern of x=0.5 composition. The pattern shows the presence of 50:50 weight % Co2Y and ZnF ferrite phases. Lattice parameters of ferrites are shown in the inset of the Fig. 1 along with the Reitvield refinement ‘R’-factors data. The lattice parameter of Co2Y ferrite was found to increase with the increase in ZnF ferrite may be due to some solubility of ZnF in Co2Y ferrite. The bulk density of x=0.5 composition (~ 4.2 gm/cc) was highest among 3 composites. The surface microstructure of x=0.5 composition (inset of Fig. 1) shows the presence of plate like Co2Y and cubic ZnF grains. Fig. 2 shows the permittivity and permeability of three composites. Permittivity and permeability of x=0.5 composition were highest among all. The miniaturization factor (n=17.4) and impedance (Z=1.2) were also highest in that composition. Hence, x=0.5 composition is the best with respect to the miniaturization factor due to better densification of the material. It may be concluded that the Co2Y-ZnF composite ferrite with tunable permittivity and permeability can be used for ultra-high frequency antenna application