Multilevel structure carbon aerogels with 99.999 % electromagnetic wave absorptivity at 1.8 mm and efficient thermal stealth

•A multi-level structure absorber was established by different scale combinations.•The electromagnetic wave absorptivity of 99.999 % was achieved at 1.8 mm.•The broad bandwidth almost covered the entire Ku-band.•The difference temperature between the surface and the ambient background was less than 5 °C.•In the far-field condition, the radar cross-section reduction value was reduced by ∼ 21.5 dB m2.