Grain-size Dependence of Absorption Characteristics of the Electromagnetic Wave Absorbers of Ferrite-SiO₂ Composites

Abstract

Grain-size dependence of electromagnetic absorbing characteristics for composite materials made of Ni-Zn ferrite and SiO₂ was investigated by using SiO₂ with various grain sizes (29µm, 30nm, 12nm, 7nm). The absorption characteristics of ferrite composites using SiO₂ of the average grain size 30nm, 12nm or 7nm were improved compared with those of ferrite composites using SiO₂ of the average grain size 29µm in the low frequency region. Furthermore, grain size dependence for composite materials of Mn-Zn ferrite with the average grain size of 130nm and SiO₂ with the average grain size of 29µm was investigated. The absorbing center frequency was shifted to the higher frequency region compared with that of Mn-Zn ferrite.