ABSTRACT Accurately controlling the particle state and clarifying the relationship between particle structure and electromagnetic wave (EMW) are crucial for the development of high‐performance EMW absorbers, which are essential to address the challenges of electromagnetic pollution and stealth technology. However, achieving both high‐temperature resistance and low‐frequency response in ceramic‐based absorbers remains a significant challenge. Herein, we propose a metal nanoparticle diffusion‐dissolution mechanism through an atomic‐level engineering strategy to effectively control the evolution of Fe nanoparticles into Fe single atoms within SiOC ceramic fibers. By precisely optimizing the nitrogen source, the regulatory mechanisms of nitrogen doping on the evolution of iron species and the resulting electromagnetic behavior are systematically investigated. Due to the interaction between Fe single atoms (Fe‐N x ) and adjacent N/C atoms, the local microstructure symmetry of SiOC is disrupted, which improves the polarization behavior of SiOC─Fe─CN and enables multiple polarization loss mechanism. Notably, the SiOC─Fe─CN‐10 fiber exhibits exceptional absorption capability with a reflection loss (RL) of −59.33 dB at an ultrathin thickness of 1.60 mm and −58.0 dB at a low‐frequency of 5.93 GHz. The effective absorption bandwidth (EAB) reaches 5.5 GHz at a thickness of 1.49 mm. It also delivers remarkable high‐temperature (≥500°C) EMW absorption performance, with an RL of −53.2 dB at a low‐frequency of 4.78 GHz, which is the high performance of SiC‐based high‐temperature absorbers currently available. Moreover, the SiOC─Fe─CN‐10 composite demonstrates favorable thermal diffusion properties. This concept of precise control over particle state provides a valuable strategy for the design of high‐performance EMW absorbers and promotes the ongoing advancement of electromagnetic technology.
Zeng et al. (2026) studied this question.