Abstract: Electromagnetic wave absorption materials featuring small thicknesses and wide effective absorption bandwidth (EAB) are highly required for next-generation portable devices, wearable electronics, and blooming military applications. However, traditional EM particle absorbents, such as carbon-based, magnetic metal-based, and MXene-based materials are always visible black, which severely hinders their utilization as microwave-stealth smart window alternatives. Therefore, it is a critical challenge to fabricate flexible windows simultaneously possessing high optical transmittance and excellent EM wave absorption properties. Herein, we prepared a transparent wood composite with an optical transmittance value of more than ∼83% through a delignification and polymer composite immersion method. The delignification process could remove the light-absorbing lignin component, and the transparent woods were realized by immersing the delignified wood into refractive-index-matched pre-polymerized acrylamide (AM) including minor silver nanowires, carbon nanotubes, and reduced graphene oxides. In addition, due to the presence of numerous polarization centers originating from hydrophilic functional groups and conductive fillers, the transparent wood composite showed superior EM absorption performance, and EAB can reach 9.5 GHz, almost occupying the whole X band (8.2-12.4 GHz) and Ku band (12.4-18 GHz) at a thickness of 2.0 mm. Furthermore, the transparent wood presented a great insulative thermal performance with a low thermal conductivity of 0.45 W m^-1 K^-1 (half of common glass). The developed transparent wood composites offered significant potential as smart energy-efficient windows with the expectation to survive military equipment and alleviate EM pollution.

Key words: Electromagnetic wave absorption, Dielectric loss, Optical transmittance, Polyacrylamide, Wood composite