Doping effect on microwave reflection characteristics for W-type ferrite/epoxy composites

The reflection properties have been studied for BaCoZnFe16O27 composites doped with 0.5 wt% CaO, Bi2O3, SiO2, and 1 wt% Nb2O5 and V2O5. For composites undoped and doped with SiO2, Nb2O5 and V2O5 two matching thicknesses, t(m1) and t(m2), and two corresponding matching frequencies, f(m1) and f(m2), are observed. t(m1) has its origin in the quarter wavelength matching condition and t(m2) is related to the magnetic resonance. As compared with the original composite, doping of CaO, Bi2O3 and SiO2 deteriorates the reflection properties of composites due to a large increase in epsilon', which leads to a mismatch between the material and free space. On the other hand, doping of Nb2O5 and V2O5 can significantly improve the reflectivity and bandwidth, due to enhanced mu(0)' and mu(max)'' max, and almost unchanged epsilon'. The two composites doped with Nb2O5 and V2O5 are potential candidates for use as EM materials with low reflectivity and broad bandwidth at microwave frequency.