Expanded graphite—Phenolic resin composites based double layer microwave absorber for X-band applications

摘要

In this investigation, double layer microwave absorbers are designed and developed with paired combination of 5 wt. %, 7 wt. %, 8 wt. %, and 10 wt. % expanded graphite-novolac phenolic resin (EG-NPR) composites, in the frequency range of 8.2–12.4 GHz. The thickness and compositional combination of the two layers constituting the absorber are optimized to achieve minimum value of reflection loss (dB) and a broad microwave absorption bandwidth. Double layer combinations showing −25 dB absorption bandwidth >2 GHz and −30 dB absorption bandwidth >1 GHz are chosen for fabrication. The total thickness of the fabricated double layer microwave absorber is varied from 3 mm to 3.4 mm. Absorption bandwidths at −10 dB, −20 dB, −25 dB and −30 dB are determined for the fabricated structure. The maximum −25 dB and −30 dB absorption bandwidth of 2.47 GHz and 1.77 GHz, respectively, are observed for the double layer structure with (5 wt. %–8 wt. %) EG-NPR composites with total thickness of 3.2 mm, while −10 dB bandwidth covers the entire X-band range.