Controllable Interface and Defects in Carbon-Coated Flaky Carbonyl Iron via Laser Ablation for Multiband Microwave Absorption

The increasing demands of fifth-generation (5G) communication technology and radar low-frequency detection systems for low-frequency wave absorption, combined with the complexity and variability of practical applications, present significant challenges in achieving effective S-band multiband electromagnetic wave absorption materials. In this study, we combined flaky carbonyl iron (FCI) with the tunable surface defects of carbon materials to fabricate heterogeneous interfaces and defective carbon shells via laser ablation technology, resulting in the development of carbon-coated flaky carbonyl iron core–shell composites (FCI@C) with multiband wave absorption properties. Compared with FCI, the FCIC1 sample, which was coated with a single carbon shell, exhibited the best absorption performance, which realized triband (S, X, and Ku-band) electromagnetic wave absorption. The effective absorption bandwidth (EAB) reaches 3.92 GHz (2.4–3.04 GHz, 8.4–10.08 GHz, and 15.68–17.28 GHz) at 8.7 mm. Density functional theory is used to reveal the enhancement of carbon shell defects on the interface polarization and multiband absorption of the Fe–C heterogeneous interface. The exceptional multiband absorption performance is attributed to the synergistic effects of multiple electromagnetic wave loss mechanisms, which arise from the heterogeneous interface and defect sites within the carbon shell. This work presents a novel approach for developing multiband absorbing materials capable of simultaneously meeting the application requirements across different frequency bands.