Development of Microwave Absorber Composed of Dual Ferrite Phase

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[Purpose] In this study, sintered bodies composed of a mixture of M and W-type phases were prepared and their electromagnetic wave absorption properties were investigated. As its magnetic properties are similar to those of M-type ferrite, Zn added BaW-type ferrite (BaZn_2-W) was chosen for this work.[Experimental] The sintered body samples had composition of BaZn_<2x>Fe_<12-x+4y> (Sn_0.5>Mn_<0.5>)x O_<19+8y> (1.2≦x≦2.0, 0.25≦y≦0.75), and were sintered at temperatures between 1473 K and 1573 K. The phases present were analyzed by X-ray diffraction (XRD), and were shown to consist of BaM and BaZn2W-type hexaferrite phases. The relative complex permeability (μr′and μr″) and permittivity (εr′and εr″) of toroibally shaped sintered samples were calculated from S-parameter values measured using a Hewlett-Packard HP8720D network analyzer, in the frequency range 0.O5〜20.O5GHz.[Results] In all samples sinlered at 1473K〜1573K with x=1.2 and y=0.5, two peaks, corresponding to the M and W-type phases, were observed in the frequency dispersion of the relative complex permeability. In the T=1473K and 1523K samples, which showe Reflection Losses (R.L.) less than -2OdB, ΔF was 2.2 and 0.7GHz, respectively. Therefore, a sintering temperature of T=1473K was selected, and the compositional ratio of M and W phases (y) was varied between 0.25 and 0.75. Almost the same matching thickness (dm) was obtained for all of the samples, however the y=0.5 sample exhibited the largest ΔF value. Therefore, in the BaZnFe10.8(Sn0.5Mn0.5)1.2O23 sample sintered at 1473K, ΔF was wider (2.2GHz) than for a M-type single phase sintered body, with a relatively small matching thickness of dm=1.Omm. It is concluded that using a two-phase microstructure composed of M and W-type hexaferrite, is an effective method of expanding ΔF.