Ultrawide Spectra Camouflage Coatings from Metallic Flake Powder

Ultrawide-spectra-compatible camouflage materials are imperative for military science and national security due to the continuous advancement of various sophisticated multispectral detectors. However, ultrawide spectra camouflage still has challenges, as the spectral requirements for different bands are disparate and even conflicting. This work demonstrates an ultrawide spectra camouflage material compatible with visible (VIS, 400-800 nm), infrared (IR, 3-5 and 8-14 μm), and microwave (S-Ku bands, 2-12 GHz). The carbon nanotubes adsorbed on porous anodic alumina/aluminum flake powder (CNTs@PAA/AFP) material for ultrawide spectra camouflage is composed of bioinspired porous alumina surface layers for low visible reflection and aluminum flake powder substrate for low infrared emissivity, while the surface of the porous alumina layers is loaded with carbon nanotubes for microwave absorption. Compared with previous low-emissivity materials, CNTs@PAA/AFP has omnidirectional low reflectance (R_avg = 0.29) and high gray scale (72%) in the visible band. Further, it exhibits low emissivity (ε_3-5μm = 0.15 and ε_8-14μm = 0.18) in the dual infrared atmospheric window, which reduces the infrared lock-on range by 59.6%/49.8% in the mid/far-infrared band at high temperatures (573 K). The infrared camouflage performance calculated from the radiation temperature of CNTs@PAA/AFP coatings is enhanced to over 65%, which is at least 4 times greater than that of its substrate. In addition, the CNTs@PAA/AFP coating achieves high microwave absorption (RL_min = -42.46 dB) and an effective absorption bandwidth (EAB = 7.43 GHz) in the microwave band (S-Ku bands) due to the enhancement of interfacial polarization and conductive losses. This study may introduce new insight and feasible methods for multispectral manipulation, electromagnetic signal processing, and thermal management via bioinspired structural design and fabrication.