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

Abstract

The reflection properties have been studied for BaCoZnFe16O 27 composites doped with 0.5 wt% CaO, Bi2O3, SiO2, and 1 wt% Nb2O5 and V2O 5. For composites undoped and doped with SiO2, Nb 2O5 and V2O5 two matching thicknesses, tm1 and tm2, and two corresponding matching frequencies, fm1 and fm2, are observed. tm1 has its origin in the quarter wavelength matching condition and tm2 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 ε′, 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 μ′0 and μ″max, and almost unchanged ε′. 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. © 2009 IOP Publishing Ltd.