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

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.