Multiscale Impedance‐Matching Engineering Enables Ultra‐Long‐Time and Stable High‐Temperature Electromagnetic Absorption in Ceramic Composites

ABSTRACT Long‐term and stable electromagnetic wave (EMW) absorption at elevated temperatures is crucial for stealth materials used in the hot parts of high‐speed aircraft. However, dielectric instability, impedance mismatch, and oxidation‐induced degradation remain major challenges for high‐temperature EMW absorption materials. Herein, a multiscale impedance‐matching strategy is developed to construct Al 2 O 3f @BN‐SiOC‐UHTC composites with integrated EMW absorption, mechanical strength, and environmental durability. The synergistic dielectric regulation enabled by multiscale interfaces and a thermal‐protective impedance layer delivers ultra‐broadband absorption over 2–40 GHz, with an effective absorption bandwidth (EAB) of 23.46 GHz at room temperature (RT) and 22.14 GHz at 1473 K. Remarkably, our material can achieve good EMW absorption after oxidation at 1473 K for 600 h, while maintaining stable performance after 30 thermal‐shock cycles and 600 s of butane‐torch ablation. The ceramic composites also exhibit a high flexural strength of 414.92 ± 41.86 MPa at RT, retaining substantial mechanical integrity at elevated temperatures. This multiscale design provides a promising route toward broadband, mechanically robust, and long‐term durable stealth materials for extreme‐temperature applications.