In search of high-performance broadband microwave absorption, the design of double-layer dielectric microwave absorbers based on dual-phase polyaniline (PA)/expanded graphite (EG) composites synthesized by in situ polymerization of aniline in different concentrations (0.00 wt.%, 0.15 wt.% and 0.25 wt.%) of EG was optimized. The developed composite reinforcers, viz. PA/EGx=0.15,0.25 and PA/EGx=0.00 (PA), were mixed at different loadings (10 wt.%, 20 wt.% and 30 wt.%) with novolac phenolic resin to form PG and PA composites, then their complex permittivity and permeability in the X-band were characterized. Using the transmission-line model, the reflection loss of single-layer absorbers of different PG and PA composites was estimated (RLc) and measured (RLm). Based on the best results, the design of the double-layer absorber was optimized by tuning the impedance matching between layers by adjusting the arrangement and thickness of the layers in the composites. Promising microwave absorption with RLm ∼ − 48 dB at 9.4 GHz along with − 20-dB and − 30-dB absorption bandwidths of 3 GHz and 2 GHz were obtained for the double-layer design comprising PG5–PA3 composite material layers. Moreover, a partially perforated double-layer design is proposed, showing enhanced absorption bandwidth due to frequency-independent impedance matching at the interface between air and the perforated layer, facilitated by the effective permittivity of the latter.
Polyaniline expanded graphite dielectric response transmission line multilayer microwave absorber
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The authors are sincerely grateful to the Department of Physics, Sibsagar College, India and Microwave Engineering Laboratory of Tezpur University India, for providing facilities to carry out the research work.