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

Abstract

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(Zn_0.8Mn_0.2)₂Fe₁₂O₂₂ [(Zn_0.8Mn_0.2)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 (Zn_0.8Mn_0.2)₂Y was 7 mm.