Abstract: Ceramic matrix composites (CMC) are widely utilized in high-temperature components of aero-engines for load-bearing and electromagnetic stealth synergy due to their superior toughening and designable electromagnetic properties. However, the design of ultra-broadband electromagnetic wave (EMW) absorption at thin thicknesses (d < 10 mm) has been difficult and focused, especially the design of metamaterial. Inspired by 3D printing technology and the structural characteristic of 2D CMC, this study ingeniously devised and proposed a novel carbon fiber gradient periodic structure in Al₂O_3f/SiOC composites to enhance the ultra-broadband EMW absorption properties at a wide temperature range. By optimizing the geometric structure parameters, the Al₂O_3f/SiOC composites with the carbon fiber gradient periodic structure have exhibited exceptional ultra-broadband EMW absorption properties at elevated temperatures and excellent mechanical performance. The composites have attained a minimum reflection loss (RL_min) of -30 dB and a high absorption efficiency of more than 84 %, ranging from 9.3 to 40 GHz at a thickness of 9 mm. Due to the temperature insensitivity of discrete periodic structures, the composites can adapt to high temperatures up to 700 °C. Additionally, compared to the Al₂O_3f/SiOC composites, the flexural strength and fracture toughness of the Al₂O_3f/SiOC composites with carbon fiber gradient periodic structure have significantly increased to 398 MPa and 15.6 MPa m^1/2, respectively. This work breaks through the limitation of the design and fabrication of 3D periodic structures in CMC, creating a novel oxide-CMC with ultra-broadband EMW absorption properties at a wide temperature range and enhanced mechanical properties.

Key words: Carbon fiber, Gradient periodic structure, Ceramic matrix composites, Ultra-broadband absorption, High-temperature