High-Performance Broadband Microwave Absorbers Using Multilayer Dual-Phase Dielectric Composites

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 insitu polymerization of aniline in different concentrations (0.00wt.%, 0.15wt.% and 0.25wt.%) of EG was optimized. The developed composite reinforcers, viz. PA/EG(x=0.15,0.25) and PA/EG(x=0.00) (PA), were mixed at different loadings (10wt.%, 20wt.% and 30wt.%) 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 approximate to-48dB at 9.4GHz along with -20-dB and -30-dB absorption bandwidths of 3GHz and 2GHz 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.