Enhanced electromagnetic wave absorption in (SiO2–C)f/(CrZrHfNbTa)C–Si3N4–SiBCN composite by defect engineering and gradient permittivity modulation

Structure and stealth integrated materials that simultaneously deliver mechanical loading and broadband electromagnetic wave (EMW) absorption performance are critical for next generation stealth aircraft. Although conventional carbon fiber reinforced ceramic matrix composites (C_f/CMCs) exhibit outstanding load-bearing capacity, their inherent EMW reflection characteristics often fail to meet stealth requirements. This work proposes a multiscale design strategy synergizing microscopic defect engineering with macroscopic gradient permittivity modulation. Accordingly, (SiO₂–C)_f/(CrZrHfNbTa)C–Si₃N₄–SiBCN composite featuring self-adaptive impedance matching and multi-mechanism EMW absorption were successfully constructed. The material demonstrates acceptable load-bearing capacity (101 ± 5 MPa) while achieving a remarkably high effective absorption bandwidth (EAB) per unit thickness (2.68 GHz mm⁻¹). More importantly, radar cross section (RCS) simulations reveal that the sample achieves a remarkable RCS reduction of 35.52 dB m². This surpasses most reported materials system, demonstrating high practical application potential. Density functional theory calculations reveals that defect engineering (lattice distortion and point defects) in the sample constructs new polarization centers at the microscopic level, which significantly enhances polarization relaxation loss for improved EMW absorption. On the other hand, macroscopic structural design (SiO_2f-C_f-SiO_2f) significantly optimizes the impedance matching, which effectively broadens EAB. The multiscale design strategy overcomes the inherent conflict between strong EMW reflection and attenuation in carbon fibers, which provides a novel material solution for stealth aircraft.