フェライト·SiO₂複合電波吸収体材料の吸収特性の改善および斜入射特性の評価

抄録

We develop conductor-backed single layered electromagnetic wave absorbers made of composite materials (spinel-type Ni-Zn ferrite, SiO₂) which can operate in the frequency region below 5GHz. Both the complex permittivity and the complex permeability of ferrite composites obeyed Lichtenecker’s logarithm mixed law. The density and the hardness were improved by adding B₂O₃. The conductance value increased and the center absorbing frequency was shifted to the lower frequency with increasing the density. The conductivity can be reduced by adding oxide such as CoO, NiO or MnCO₃. The complex permeability, however, decreases for the ferrite composites added CoO or NiO but does not change for that added MnCO₃. The center absorbing frequency of the ferrite composites added MnCO₃ can change in the wide frequency range by varying only the thickness without changing the composition. Absorbing characteristic of electromagnetic wave absorbers added CoO or NiO having required center absorbing frequency below approximately 5GHz can be achieved by coating of ITO thin film with the suitable thicknesses or resistivity without changing the composition. The limit of incident angle of the electromagnetic wave for the absorption above 90%, is approximately 35° for both TE and TM modes. The incident angle characteristic in not degraded for samples applied ITO thin film.