Enhanced Microwave Absorption Properties of Double-Layer Absorbers Based on Spherical NiO and Co0.2Ni0.4Zn0.4Fe2O4 Ferrite Composites

Microwave absorption properties of spherical NiO particles and Co 0.2 Ni 0.4 Zn 0.4 Fe 2 O 4 (CNZF) ferrites with single-layer and double-layer absorbers were studied in the frequency range of 2–18 GHz. The spherical NiO particles were synthesized by using a hydrothermal process, while the CNZF powders were prepared by using a sol–gel autoignition method. The double-layer absorbers, composed of 30 wt% NiO as matching layer and 30 wt% CNZF as absorption layer, with a total thickness of 3.2 mm, exhibited a maximum reflection loss ( R L ) of –67.0 dB at 9.2 GHz and an effective absorbing bandwidth below –10 dB to be 3.9 GHz from 7.0 to 10.9 GHz. The excellent microwave absorption performance of the double-layer absorbers should be ascribed to the high impedance matching ratio, the great microwave attenuation capability, and well-coupled layer.