Optimization of the Carbon Coating of Honeycomb Cores for Broadband Microwave Absorption

A simple and fast coating method of honeycomb cores for microwave absorption has been described. The honeycomb cores with two different thicknesses (5 and 20 mm) coated with thermoplastic resin filled with carbon powder as lossy filler in 5, 10, 15, and 20 wt% have been tested for microwave absorption in 2 - 18-GHz frequency range. The 5-mm-thick honeycomb has shown absorption bandwidth of 14 GHz for maximum absorption of -6 dB (75%) with 15 wt%. filler content. However, the percentage of the filler was decreased to 10 wt% in 20-mm-thick honeycomb absorber for maximum absorption over a wide frequency range. The honeycomb sample with 10 wt% filler has bandwidth of 18 GHz for -7 dB (80%) reflection loss. The reflection loss measurements of coated honeycomb cores have also shown that use of E-glass fiber/epoxy composite can enhance the performance of the honeycomb absorber. The combination of a microwave absorbing nanocomposite and the coated honeycombs has been resulted in inferior absorption properties in 2 - 18-GHz frequency range.