Design optimization and fabrication of a wideband microwave absorber based on dual-phase dielectric semi-metallic nanocomposite

Dual-phase nanocomposites consisting of dielectric polyaniline (PA) of diameter similar to 50 nm and semi-metallic expanded graphite (EG) were synthesized by in situ emulsion polymerization technique. This involved integrating EG in varied proportions of EG (0.00, 0.15, and 0.25 wt %) into PA and mixing with novolac phenolic resin (NPR) (10, 20, and 30 wt %) to tailor the microwave absorption properties ofrelative complex permittivity epsilon(r)(omega) = epsilon(r)' - j epsilon(r)'', where epsilon(r)'' and epsilon(r)'' are real and imaginary parts of complex permittivity in the X-band frequency. The measured frequency-dependent epsilon(r)(omega) values showed significantly enhanced values for PA/EG-NPR nano-composites with epsilon(r)' similar to 14.5 epsilon(r)'' similar to 25.6, and (epsilon(r)''/epsilon(r)') > 1.5 compared with PA-NPR nanocomposites with (epsilon(r)''/epsilon(r)') > 0.25 and were analyzed using the principle of capacitance variation with filler concentration. Based on the Transmission Line Model, design optimization of single-layer microwave absorbers was performed for the developed nanocomposites. The fabricated absorber exhibited measured reflection loss RLm similar to 32 dB at 9.7 GHz and RLm similar to 17 dB at 10.9 GHz for 30 wt % PA/EGNPR (EG = 0.15) composite of thickness 3 mm and 20 wt % PA/EG-NPR (EG = 0.25) of thickness 2.5 mm, respectively, with -10 dB absorption bandwidth of 2.4 and 1.7 GHz in the X-band. A triangular-lattice perforated design for PA/EG composite was proposed to enhance the broad impedance matching and absorption bandwidth in the X-band.