Fabrication and Characterization of Hybrid Natural Fibre-Reinforced Sandwich Composite Radar Wave Absorbing Structure for Stealth Radomes

Natural fibre based sandwich composite wave absorbing structures were prepared and characterized for stealth and radome applications. The principal aim of this research was to develop a novel sandwich radar wave absorbing composite structure and evaluating their wave transmission and flexural properties. Fibres such as wool, silk, E-glass, aramid and wave absorbing foams like balsa wood, PVC and PMI were used for making wave absorbing sandwich composites. The composites were prepared using autoclave vacuum bag degassing method followed by post curing at 120 degrees C. The radar wave transmission characteristics were investigated using stealth radomes by partially replacing the traditional E-glass and aramid fibre structure with a frequency selective surface (FSS) with standard parameters. The free space measurement technique was used to examine the radar wave transmission characteristics in the X-band frequency range (8.2-12.4 GHz). Three point bending test also performed to identify the flexural strength of sandwich composite setup to ensure the bending rigidity. A highest wave transmission of 87.7% at bandwidth 0.83 GHz in - 1 dB with flexural strength of 44.2 MPa was observed for sandwich composite type 3c, which contains aramid/epoxy composite + balsa wood + silk/epoxy structure. The SEM micrographs showed highly reacted and toughness improved matrix phase for type 3c composite sandwich.