Polyurethane foam-based radar absorbing sandwich structures to evade detection

Polyurethane foam-based sandwich structures were developed for radar absorbing properties together with load bearing capability. The sandwich construction of radar absorbing structure comprised glass fiber epoxy matrix composite containing carbon black as front face skin, carbon fiber epoxy matrix composite as back face skin, and polyurethane foam reinforced with carbonyl iron or graphite powder as the core material. The quantity of carbon black in the front face skin composite was varied from 6 wt.% to 8 wt.%, while the loading of carbonyl iron and graphite powder in foam core was varied from 30 wt.% to 55 wt.% and 5 wt.% to 30 wt.%, respectively. The compression molding technique was used to prepare face skins and sandwich structures. Different combinations of the sandwich structures were characterized for a frequency range of 2–18 GHz using free space measurement method. The maximum attenuation of −31.85 dB was observed in a combination containing 6 wt.% carbon black in front face skin and 20 wt.% graphite powder in the foam core. The total reduction in radar cross-section demonstrated almost zero radar signature at nine different frequencies, whereas broad range attenuation of −10 dB was achieved.