Robust Multiscale Superhydrophobic Armor for Corrosion-Resistant Millimeter-Wave and Terahertz Composite Absorbers

Efficient electromagnetic absorbers rarely maintain long-term reliability in harsh environments, primarily because the exposed interface, crucial for wave coupling, is the most vulnerable to impedance mismatch and chemical degradation. Here, we develop a hierarchical superhydrophobic armor on absorber composites by filling prepatterned micrometer-scale cavity arrays with hydrophobic nanoparticles. Built on a polyimide-based composite, this multiscale architecture simultaneously enables a smooth impedance transition and robust surface protection. The resulting layer retains its structural integrity and corrosion resistance under severe mechanical abrasion as well as strongly acidic, alkaline, and saline conditions while preserving electromagnetic absorption in the terahertz (THz) band. More importantly, it effectively blocks oxidative ingress to internal carbonyl iron powder (CIP) fillers, thereby maintaining resonance-dominated W-band absorption without a frequency drift. Standard neutral salt spray tests further demonstrate that composites with the optimized protective layer exhibit neither detectable iron oxide phases nor absorption peak shifts after corrosion exposure. This work establishes a scalable interfacial design strategy for electromagnetic absorbers that must operate efficiently and reliably under harsh service environments.