Gradient-Engineered Liquid-Metal Magnetic Hollow Microspheres for Flexible and Broadband Microwave Absorption.

The development of high-performance flexible microwave absorption materials (MAMs) is crucial for next-generation wearable stealth and electromagnetic protection, yet it remains challenging to integrate ultra-wideband absorption, lightweight, and mechanical robustness in a single material. Here, a novel collision-mediated energy transfer strategy coupled with a pH-regulated deposition process is proposed to fabricate liquid-metal magnetic hollow microspheres with a compositional-gradient structure. This hierarchical architecture enables efficient impedance matching and multi-mode energy dissipation. As a result, the material achieves an effective absorption bandwidth (EAB) of 9.0 GHz at a thickness of 2.39 mm. In addition, a reflection loss below -20 dB is obtained at 1.46 GHz, indicating highly competitive performance among hollow-microsphere-based MAMs. Importantly, the absorption performance remains stable under mechanical deformation. The material maintains an EAB of 8.0 GHz even after 100% tensile strain, demonstrating its potential for flexible applications. Multiscale quantitative analyses reveal synergistic magnetic-dielectric coupling loss mechanisms. Practical radar cross-section simulations corroborate the exceptional stealth capability, with only 0.16% of incident energy reflected. This work provides a viable strategy for designing flexible and broadband microwave absorption materials.