Dual-layer self-healing composites with temperature-responsive intelligent broadband microwave absorption

Wireless technology advances exacerbate electromagnetic interference challenges, fueling the demand for microwave absorption (MA) materials with broadband compatibility and adaptive tunability. This work proposes a dual-layer intelligent broadband MA composite. The upper and lower layers exhibit complementary microwave loss characteristics across the frequency spectrum. Synergistically, this ensures high-efficiency MA that seamlessly covers the entire 2-18 GHz band. Specifically, the dual-layer structure utilizes carbonyl iron powder (CIP)/boron nitride (BN) and FeSiAl/BN/vanadium dioxide (VO₂) composite powders, prepared via plasma ball milling, for the upper-layer and lower-layer absorbers, respectively. The BN coating modulates the dielectric properties of the composite powders. As a result, the upper layer, featuring a lower characteristic impedance, primarily attenuates X/Ku-band microwaves, while the lower layer, with a higher characteristic impedance, is designed to absorb S/C-band microwaves. Strong magnetic loss from CIP in the X/Ku band and FeSiAl in the S/C band further enhances layer-specific MA within their target frequency ranges. Ultimately, this structure achieved an ultra-wide effective absorption bandwidth (EAB) of up to 13.49 GHz at a thickness of 3.70 mm. Compared with the application of a single magnetic absorber, it demonstrated a 48% enhancement in EAB. Additionally, the VO₂ enables dynamic Ku-band MA modulation through insulator-to-metal transition, yielding a maximum tunable EAB range (ΔEAB) of 8.35 GHz. A dynamic poly(urethane urea) matrix enables the composite to achieve adhesive-free layer assembly through self-healing. Thus, this composite is promising for applications in 5G/6G telecommunications, multi-band radar and health-monitoring flexible devices.