Bionic Interface Engineering Enables Ultrathin, Strong, and Broadband Microwave Absorbers

To address the challenges of dielectric constant surge and impedance mismatch caused by particle agglomeration in highly filled carbonyl iron/polyurethane (CIP/PU) composite films, we developed a surface modification strategy for CIP using a KH550 silane coupling agent (0-2 wt %). Inspired by the adhesive pads and climbing mechanisms of climbing plants, this bioinspired interface design establishes a CIP-PU ″molecular bridge″, enhancing interfacial compatibility. At 1 wt % KH550, CIP dispersion is markedly improved, disrupting the three-dimensional conductive network. This yields a 44% increase in tensile strength (10.104 MPa) and a 36.8% reduction in dielectric constant. Furthermore, the film achieves a minimum reflection loss of -17.09 dB and an effective absorption bandwidth (RL ≤ -10 dB) of 6.7 GHz (10.3-17 GHz) at a thickness of only 1 mm. This bionic interface engineering strategy overcomes the longstanding bottleneck in synchronizing impedance matching and mechanical performance in high-filler-content (85 wt %) composite absorbers.