Wood Carbon Sponge/SiO₂ Aerogel Composites with Anisotropic Broadband Microwave Absorption, Elastic Resilience, and...

Biomass-derived carbon aerogels have attracted considerable interest for lightweight microwave-absorption owing to their hierarchical porosity and renewability. While the structural anisotropy of natural wood is well recognized, its consequences for electromagnetic response remain largely unexplored. Herein, we utilize SiO₂ aerogel-incorporated wood-derived carbon sponge as a model system to investigate its electromagnetic anisotropy in the axial, radial, and tangential directions. Governed by the aligned cellular architecture, a robust permittivity ordering (tangential > radial > axial) is revealed. Notably, the composite exhibits pronounced anisotropic absorption: the tangential direction achieves a minimum reflection loss of -64.1 dB, the radial direction delivers an ultra-broadband effective absorption bandwidth of 11.6 GHz (covering the entire X and Ku bands) at a thickness of only 4.95 mm, and the axial direction also maintains strong absorption, with the overall performance surpassing most biomass-derived carbon aerogels at comparable thicknesses. The composite also reveals a low thermal conductivity of ∼0.04 W/(m·K) and anisotropic compressibility. This work clarifies the intrinsic structure-electromagnetic-mechanical-thermal correlations in anisotropic wood carbon sponges and offers a bioinspired paradigm for advanced lightweight stealth materials with concurrent thermal insulation.