The development of stealth technology for military applications and increasing concerns of electromagnetic pollution have garnered interest to design microwave absorbing materials with wide absorption bandwidth and effective absorption properties. Two batches of samples as a potential radar absorbing material were prepared in this study: single-layer and double-layer nanocomposite mixtures of graphite and barium hexaferrite nanoparticles. Characterizations of electromagnetic and microwave absorbing properties were carried out in the frequency range of 8?12 GHz (X-band) and 12?18 GHz (Ku-band). Single-layer samples with thickness of 2 mm showed optimal absorption properties with minimum reflection loss of -20.5 dB at 11.8 GHz for X-band and -20.7 dB at 14.7 GHz for Ku-band, displaying bandwidths of 0.6 GHz for the former and 3.8 GHz for the latter at -10 dB. On the other hand, double-layer samples made of 1 mm thick barium hexaferrite matching layer and 2 mm thick graphite absorbing layer showed optimal absorption properties with minimum reflection loss of -30.0 dB at 9.2 GHz for X-band with narrower bandwidth of 0.6 GHz. The microwave absorption properties of these nanocomposites were attributed to combined effect of dielectric loss from graphite and magnetic loss from ferrite.

Microwave absorption properties were systematically studied for double-layer carbon black/epoxy resin (CB) and Ni0.6Zn0.4Fe2O4/epoxy resin (F) nanocomposites in the frequency range of 8 to 18 GHz. The Ni0.6Zn0.4Fe2O4 nanoparticles were synthesized via high energy ball milling with subsequent sintering while carbon black was commercially purchased. The materials were later incorporated into epoxy resin to fabricate double-layer composite structures with total thicknesses of 2 and 3 mm. The CB1/F1, in which carbon black as matching and ferrite as absorbing layer with each thickness of 1 mm, showed the highest microwave absorption of more than 99.9%, with minimum reflection loss of −33.8 dB but with an absorption bandwidth of only 2.7 GHz. Double layer absorbers with F1/CB1(ferrite as matching and carbon black as absorbing layer with each thickness of 1 mm) structure showed the best microwave absorption performance in which more than 99% microwave energy were absorbed, with promising minimum reflection loss of −24.0 dB, along with a wider bandwidth of 4.8 GHz and yet with a reduced thickness of only 2 mm.