Low Temperature Sintering and Characterizations of Co-Ti Substituted SrFe12O19 M-type Hexagonal Ferrites for High frequency Antenna Applications

Abstract

The objective of the work was to sinter the Co-Ti substituted SrFe12O19 ferrite at 900oC using sintering additives and to use the low-temperature sintered ferrite for high frequency antenna substrate materials applications. SrCo1.5Ti1.5Fe9O19 ferrite was synthesized by two different routes; (a) sol-gel combustion and (b) solid-state reaction. Although the properties of the ferrite synthesized by sol-gel route were marginally higher than the ferrite prepared by solid state route, the ferrite synthesized by solid state route was used for low temperature sintering experiments due to its economical and simple processing technique. The different sintering additives like; (a) B2O3, (b) Bi2O3/+B2O3, (c) B2O3+CuO/ZnO, and (d) B2O3-Bi2O3-SiO2-ZnO (BBSZ) glass were used to study the sintering behavior of SrCo1.5Ti1.5Fe9O19 ferrite at 900oC. The 5wt% B2O3 sintering additive was proposed for the ferrite, which provides bulk density ~4.0 g/cc, equivalent ε~17 and μ~18, higher miniaturization factor (n=17.49) and good impedance matching (Zi=1.02). Bi2O3 or (Bi2O3+B2O3) additives were not so efficient like 5wt% B2O3 additive. The ferrite containing 5wt% Bi2O3 showed comparatively lower properties like; bulk density ~3.57 g/cc, ε~12.5, μ~13, n=12.74, and Zi=1.01. In the case of different combinations of B2O3+ZnO/CuO additives, 4wt% B2O3+6wt%ZnO (4B6Zn) composition was found efficient with respect to only higher bulk density achievement (~4.62 g/cc), as ε (~13) and n (~14.4) values were lower compared to 5wt% B2O3 added ferrite. The 5wt% BBSZ glass additive was found equally effective like 5wt% B2O3 additive, where the bulk density ~ 4.3 g/cc, n = 17.5 and Zi = 0.99 and about equivalent ε and μ (~17.5) were achieved. For comparison with SrCo1.5Ti1.5Fe9O19 ferrite, BaCo1.5Ti1.5Fe9O19 ferrite was also synthesized and low temperature sintered using 5wt% B2O3 and 5wt%. BBSZ glass additive. The BBSZ glass additive was found more efficient than B2O3 additive for BaCo1.5Ti1.5Fe9O19 ferrite. Finally, microstrip-fed cylindrical antennas based on low-temperature sintered SrCo1.5Ti1.5Fe9O19 and BaCo1.5Ti1.5Fe9O19 ferrites were designed, fabricated and characterized. BBSZ glass containing SrCo1.5Ti1.5Fe9O19 ferrite showed the antenna parameters; return loss ~ -34 dB, gain ~ 5.23 dB, VSWR ~ 1.05 and bandwidth (S11<-10dB) of 133 MHz at fr ~ 10.45 GHz. In the case of BBSZ glass containing BaCo1.5Ti1.5Fe9O19 ferrite, the return loss ~ -32 dB, VSWR ~ 1.03 and bandwidth of 98 MHz were found at fr ~ 8.91 GHz. The demonstrated results indicate that 5wt% B2O3 and 5wt%. BBSZ glass assisted low temperature sintered SrCo1.5Ti1.5Fe9O19 ferrite will be a better candidate for high-frequency antenna substrate material application.