Air layer-engineered Cf@void@SiCnf composites for enhanced electromagnetic wave absorption

Conventional carbon-based absorbers often suffer from poor impedance matching and limited loss mechanisms, which hinder their practical effectiveness. In this work, we propose a novel strategy that combines structural engineering with interfacial modulation to construct a hollow-structured composite, denoted as Cf@void@SiCnf. This architecture consists of a Cf core, a tunable air interlayer, and a shell of silicon carbide nanofibers (SiCnf), fabricated through chemical vapor deposition (CVD) followed by controlled oxidation. The introduction of an interfacial air layer between the carbon fiber core and SiC nanofibers significantly improved impedance matching and interfacial polarization. As a result, the composite achieves a minimum reflection loss (RLmin) of −59.21 dB at 6.96 GHz (2.30 mm thickness) and a maximum effective absorption bandwidth (EABmax) of 2.48 GHz at 1.0 mm. Additionally, the air-layer architecture imparts improved thermal insulation, when placed on a 357.3 °C hot surface, the composite's outer surface remains as low as 128.8 °C (after 5 min), indicating its promise for multifunctional thermal management applications. This study highlights the critical role of structural tuning-especially air layer design-in developing impedance-matched, high-performance EMW absorbers.