Low loss Z-type Hexaferrites with Bi₂O₃ Additives for Ultra-high Frequency Antenna Applications

Abstract

The Z-type ferrites of nominal composition Ba₃Co₂Fe₂₄O₄₁+x wt% Bi₂O₃, where x=0.25, 0.5, 1.0, 1.5, 2.0, were prepared by conventional ceramic processes. The influence of Bi₂O₃ content on the bulk densities, microstructures, magnetic and dielectric properties of Z-type ferrite samples were systematically examined so as to obtain materials with low magnetic and dielectric loss tangent over a frequency ranging from 600 to 800 MHz. The experimental results showed that addition of Bi₂O₃ lowered the sintering temperature (1 020 ℃) and then reduced the average grain size (<2 μm) and enhanced the resistivity (>2.68×10⁸ Ω•cm) dramatically, which consequently decreased the magnetic and dielectric loss. Additionally, the low loss factors were observed at the Bi₂O₃ content x = 1.0, i e, tan δ _μ/μ’ = 0.013 and tan δ _ε/ε’ = 0.001 at 800 MHz, and such materials could be used for antennas miniaturization from 600 to 800 MHz.

Keywords

low loss / Z-type ferrites / grain size / antennas