Electrochemically tunable Fe3+-incorporated hydrogels as structural microwave absorbers via battery-integrated design

All-dielectric microwave absorbers have made significant progress in the fields of broadband absorption, conformal design, and environmental durability. However, once the existing absorber is prepared, its electromagnetic parameters are often fixed, and it is difficult to achieve real-time performance control, which limits its application in intelligent stealth and tunable electromagnetic shielding. Inspired by redox-controlled ion valence modulation in redox flow batteries, a structural microwave absorber using Fe3+-incorporated hydrogels as the functional medium with tunable properties was designed. By connecting external charge and discharge circuits, the dynamic transitions between Fe2+/Fe3+ states are precisely controlled, inducing real-time modifications in the material's complex permittivity/permeability. This approach enables on-demand tuning of electromagnetic properties within the X-band (8–12 GHz). The structural absorber based on Fe3+-incorporated hydrogels can achieve 90% absorption in the frequency range of 8.3–10.9 GHz. As regulation progresses, the peak frequency changes continuously from 9.79 to 9.09 GHz. The demonstrated absorption adjustment strategy of redox material establishes an alternative approach for further developing tunable microwave absorbers with controlled peak frequency.