Functionally Graded Tunable Microwave Absorber with Graphene-Augmented Alumina Nanofibers

Abstract

Graphene is currently attracting attention for radiation absorption particularly at gigahertz and terahertz frequencies. In this work, composites formed by grapheneaugmented γ-Al 2 O 3 nanofibers embedded into the α-Al 2 O 3 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-Al 2 O 3 -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-Al 2 O 3 fillers. The results prove a remarkable potential of the fillers and various multilayer designs for broad-band and frequency-specific microwave absorbers.

Ultra‐Wideband Integrated Graphene‐Based Absorbers for Terahertz Waveguide Systems

“…Comparison of SE A and SE R for graphene‐based foam type absorbers reported in [ 12,31 ] [ 35,41–46 ] and that reported here (GAIN) at the minimum and maximum measured frequency. The SE A data has been normalized to the thickness of each material to allow a direct comparison.…”

“…Two additional defect‐induced peaks D’ (overlapping with the G peak) and D + D’ at 2915 cm −1 are observed, which are also attributed to the presence of graphene flakes covering the rough surface of the nanofibers, as was previously shown by transmission electron microscopy in. [ 41 ] The XPS spectrum of Sample 2 (Figure 3d) also illustrates the presence of the graphene coating as a thin layer and the expected alumina oxide peaks. The combined Raman and XPS spectra confirm that the integration method outlined above (grinding, sonication, and vacuum filtration) did not chemically modify the GAIN structure as compared to the original material.…”

“…This effect was also observed in ref. [41] where all measured samples displayed high reflectivity. The remaining incident signal penetrates into the material, where it induces currents in the GAIN fibers due to the presence of electric dipoles.…”

“…This value was extracted via curve-fitting of the measured SE A and is in good agreement with the DC conductivity ranges reported for GAIN in ref. [41] and represents the effective high-frequency conductivity of the absorber material at room temperature. The SE T of both samples exceeds 20 dB at all frequencies, where absorption (SE A ) is seen to be the dominant shielding mechanism.…”

“…A complete analysis of the microstructure of GAIN samples prepared using the methods described here can be found in ref. [41].…”