Hierarchically Porous Multiphase Si‐Based Ceramics with Synergistic Electromagnetic Wave Absorption Mechanisms

Abstract The development of high‐performance electromagnetic wave absorbers is critical for mitigating electromagnetic pollution in modern electronic and communication systems. Here, a scalable strategy is developed to fabricate hierarchically porous, multiphase Si‐based ceramics (Si x ‐O y ‐C z ) via one‐step activation of carbon‐rich polycarbosilane precursors. The resulting material integrates β‐SiC crystals, amorphous SiOC, and conductive carbon within a tunable porous architecture. This combination creates abundant heterogeneous interfaces, defect structures, and enhanced impedance matching. The optimized sample achieves a minimum reflection loss of −70.44 dB at just 1.79 mm thickness and a broad 4.32 GHz bandwidth at a matching thickness of 1.86 mm. Structural, dielectric, and radar simulation analyses reveal that interfacial polarization, dipolar polarization, conduction loss, and pore‐induced scattering work synergistically to dissipate electromagnetic energy. This work offers a simple, cost‐effective approach to engineer next‐generation ceramic EMW absorbers.