A gigahertz-range electromagnetic wave absorber with wide bandwidth made of hexagonal ferrite

A thin electromagnetic wave absorber has been investigated; it is composed of hexagonal ferrite and retains high permeability even in the gigahertz-range. The grid-type wave absorber composed of the hexagonal ferrite was examined to broaden the bandwidth in a gigahertz-range by introducing free space in the direction perpendicular to the electric field, which decreased total permittivity. Absorbers made of Ba3Co2Fe24O41 (Co2Z) and Ba2(Zn0.8Mn0.2)2Fe12O22 [(Zn0.8Mn0.2)2Y] showed wide bandwidths of 1.8–5 GHz and 1.5–4.5 GHz (≳15 dB), respectively, when the free space was 37% (v/v) and the thickness of the ferrite was about 5 mm. Increasing the free space led to a wider bandwidth: 1.7–9 GHz was achieved with a 50% (v/v) of free space when the thickness of the (Zn0.8Mn0.2)2Y was 7 mm.