FSS Integrated Hybrid Nanocomposite Microwave Absorber Structure for Stealth Applications

In this work, a hybrid microwave absorber (MA) comprising the frequency selective surfaces (FSS) and a thin lossy nanocomposite sheet, for stealth technology in the X-band (8.2-12.4 GHz) is proposed. The first step here requires the synthesis of exfoliated graphite (EG) and the barium strontium titanate (BST) fillers using the microwave-assisted intercalation and sol-gel techniques, respectively. The EG (4 wt%) and BST (10 wt%) fillers are then embedded into the epoxy resin to obtain the EGBST lossy nanocomposite sheet. The reflection coefficient (S11) of up to 13.7 dB covering a 10-dB absorption bandwidth of 1.94 GHz from 7.92-9.86 GHz is attained for this nanocomposite sheet having 2.1 mm thickness. Afterwards, the EGBST nanocomposite sheet is integrated with an optimized FSS layer to realize a hybrid MA (HMA) structure to enhance the overall absorption bandwidth. The optimized HMA structure enhances the 10-dB absorption bandwidth of the resultant sample to 3.67 GHz (8.12-11.79 GHz) covering 90% of X-band for a thickness of just 2 mm $(\sim \lambda / 15)$, attaining a minimum reflection coefficient of $-28 \mathrm{~dB}$. The proposed nanocomposite-based hybrid microwave absorber can potentially be used for the radar applications conforming to the stealth technology.