Interfacial polarization-dominated electromagnetic attenuation in biomass-origin porous carbon materials

Biomass-derived porous carbons have emerged as promising microwave absorbers owing to their low density, sustainability, and tunable microstructures; however, achieving ultrathin thickness, broadband absorption, and strong electromagnetic attenuation simultaneously remains a significant challenge. Herein, a multifunctional magnetic porous carbon material was fabricated using waste balsa wood as a renewable precursor through a combined delignification, solvothermal deposition, and high-temperature carbonization strategy. By regulating the carbonization temperature, multiple magnetic phases including Fe₃O₄, FeO, and metallic Fe were in situ generated and uniformly embedded within the three-dimensional carbon framework, giving rise to abundant heterogeneous interfaces. The optimized composite (CMBW-3) exhibited an ultralow reflection loss of -64.0 dB at a thickness of only 1.4 mm, along with a broad effective absorption bandwidth covering most of the Ku band. Electromagnetic parameter analysis and Cole-Cole plots reveal that the superior microwave attenuation originates from synergistic dielectric and magnetic losses, dominated by interfacial polarization, conductive loss, and magnetic resonance. Furthermore, radar cross-section simulations demonstrate a remarkable RCS reduction of up to 33.4 dB m², indicating excellent electromagnetic stealth capability. The material also shows favorable flame retardancy and rapid Joule heating response, highlighting its multifunctional potential. This work provides a sustainable and efficient strategy for converting biomass waste into high-performance, ultrathin microwave absorbers for electromagnetic stealth and related applications.