Constructing gradient impedance in hybrid C/SiC Fiber for ultra-wideband radar cross section reduction

Balancing impedance matching and attenuation capabilities is always a challenge in achieving efficient broadband microwave absorption, and single-layer structures often find it difficult to balance these two points. In this study, carbon fiber and silicon carbide fiber were arranged in a grid in a PVC matrix to construct a multi-layer gradient microwave absorber. By optimizing the stacking order of fiber arrays with different spacing and composition, a gradient impedance structure was developed to minimize wave impedance mismatch. Experimental results show that the optimized five-layer structure (configuration 51,234) exhibits excellent absorption performance at 90° polarization, achieving an ultra-wide effective absorption bandwidth (EAB) of 14.1 GHz (3.9–18 GHz) and a minimum reflection loss (RL) of −34.2 dB at 8.0 GHz. HFSS-based numerical simulations reveal potential loss mechanisms: carbon fibers provide strong conduction losses and magnetic resonance, while semiconductor silicon carbide fibers play a dual role in impedance regulation and auxiliary absorption. In addition, the electrical heterogeneity at the Cf/SiCf intersection induces significant Maxwell-Wagner-Sillars (MWS) interface polarization, further enhancing energy dissipation. This study confirms that the construction of multi-layer gradient structures using hybrid fiber arrays is an effective strategy for the development of high-performance broadband absorbing materials.