Double-layer microwave absorber based on CoFe2O4 ferrite and carbonyl iron composites

The microwave absorption properties of carbonyl iron (CI) and CoFe2O4 ferrite with single-layer and double-layer composite absorbers were investigated based on the electromagnetic transmission line theory and the impedance matching principle in the frequency range from 2 GHz to 18 GHz. XRD and SEM were used to characterize the structure of the powdered composites. Coaxial method was used to measure the electromagnetic parameters of CI and CoFe2O4. The reflectances of the matching and absorbing layers of different thicknesses and orders were also calculated. The results show that using CoFe2O4 as matching layer and CI as absorbing layer can greatly expand the coating absorption bandwidth and decrease the reflectance peak. Double-layer absorbers have much better microwave absorption properties than single-layer absorbers. The microwave absorption properties of the double-layer structure are influenced by the coupling interactions between the absorbing and matching layers. The double-layer microwave absorbers with reflection loss less than −10 dB over the range from 8.6 GHz to 18 GHz (the absorption bandwidth is 9.4 GHz), which almost covers the X-band (8.2 –12.4 GHz) and the whole Ku-band (12.4–18 GHz) were achieved when the thicknesses of CoFe2O4 and CI were 2.4 and 0.5 mm, respectively.