Functionally Graded Tunable Microwave Absorber with Graphene-Augmented Alumina Nanofibers
Ali Saffar Shamshirgar, Rocío Estefanía Rojas-Hernández, Girish C. Tewari, J.F. Fernández, Roman Ivanov, Maarit Karppinen, Irina Hussainova
Abstract
Graphene is currently attracting attention for radiation absorption particularly at gigahertz and terahertz frequencies. In this work, composites formed by graphene-augmented γ-Al2O3 nanofibers embedded into the α-Al2O3 matrix are tested for X-band absorption efficiency. Composites with 15 and 25 wt % of graphene fillers with shielding effectiveness (SE) of 38 and 45 dB, respectively, show a high reflection coefficient, while around the electrical percolation threshold (∼1 wt %), an SE of 10 dB was achieved. Furthermore, based on the dielectric data obtained for varying fractions of graphene-/γ-Al2O3-added fillers, a functionally graded multilayer is constructed to maximize the device efficiency. The fabricated multilayer offers the highest absorption efficiency of 99.99% at ∼9.6 GHz and a full X-band absorption of >90% employing five lossy layers of 1–3–5–15 and 25 wt % of graphene/γ-Al2O3 fillers. The results prove a remarkable potential of the fillers and various multilayer designs for broad-band and frequency-specific microwave absorbers.