Topological fractal multifunctional metamaterial with broadband microwave absorption and hydrophobic characteristics

Developing microwave absorbing metamaterials with broadband absorption and subwavelength thickness holds significant engineering value. To achieve broadband absorption without increasing thickness, we developed a topological fractal-nested honeycomb metamaterial, validated using an arch measurement system over 2–18 GHz. Further simulations based on the finite element method and transmission line theory demonstrate that the topological fractal structure enhances microwave absorption through the dual effects of electric field superposition and directional magnetic coupling. Notably, this directional coupling effect is a novel discovery in cellular metamaterials. The structure simultaneously induces edge diffractions, optimizes impedance, and changes microwave phases, thereby enhancing microwave absorption performance. At 2 mm thickness, the topological fractal-nested honeycomb metamaterial achieves absorption bandwidth of 9.8 GHz for reflection loss (RL) lower than −10 dB, covering almost the whole X and Ku bands. It simultaneously achieves peak radar cross section (RCS) reduction of 16 dBm² at incidence of 0°, while maintaining RCS below −10 dBm² across wide angular angles of ±90°. In addition, a hydrophobic surface with a 143° contact angle is prepared by SiO₂ nanoparticle spraying. This surface enables self-cleaning while maintaining microwave absorption performance. This work proposes a multifunctional metamaterial design and reveals the intrinsic correlation between structural topology and electromagnetic response.