• • Fe3C@NCNTs/CMTs calcined at 800 °C achieves a minimum reflection loss of –35.8 dB and an effective absorption bandwidth of 7.02 GHz at 1.7 mm thickness, with only 10 wt% filler loading, enabling lightweight, broadband shielding for Ku/X band applications.
• • The hierarchical structure combines Fe3C magnetic nanoparticles with nitrogen-doped carbon nanotubes on carbon microtubes, providing dual dielectric-magnetic loss mechanisms that optimize impedance matching and attenuation.
• • Calcination temperature critically tunes crystallinity: 800 °C yields optimal performance, while lower temperatures reduce magnetic loss and higher temperatures may degrade dielectric properties, as evidenced by comparative analysis.
• • The use of biomass cattail as a carbon precursor offers a sustainable, low-cost route to high-performance absorbers, with the synthesis process being scalable via chemical vapor deposition.