Sea Urchin-like Fe ₂ O ₃ /PPy Composites for Enhanced Electromagnetic Wave Absorption in C–X Fusion Band

In electromagnetic wave absorption, the C–X fusion band, positioned at the intersection of the C and X bands, offers a unique combination of strong signal penetration and high-resolution detection, making it a crucial frequency range for advanced communication and radar systems. In this study, a sea urchin-like Fe 2 O 3 /polypyrole (PPy) (SFOP) composite was successfully synthesized via a simple hydrothermal method followed by in situ polymerization. The unique three-dimensional structure of SFOP features a high specific surface area and abundant interfaces, which significantly enhanced electromagnetic wave attenuation through multiple synergistic loss mechanisms. The optimized SFOP sample achieved a minimum reflection loss (RL min ) of −56.4 dB at a thickness of 3 mm and exhibited an effective absorption bandwidth of 3.2 GHz within the C–X fusion band (6.6–9.8 GHz). In contrast, the nanoparticle form of Fe 2 O 3 /PPy (NFOP) achieves a RL min of −26.8 dB at 4.9 GHz at a thickness of 1.5 mm, corresponding to absorption in the C-band region. This result highlights the importance of the sea urchin-like morphology, which provides a synergistic effect that enables enhanced and broader absorption across the C–X fusion band range. With its outstanding absorption performance and low-cost scalability, this material holds strong promise for electromagnetic compatibility systems.