Multiscale Magnetic–Dielectric Coupling in Bidirectionally Aligned Multilayer Graphene/FeSiAl Aerogels for Broadband Electromagnetic Wave Absorption

Lightweight electromagnetic wave (EMW) absorbers with broad attenuation bandwidths are highly desirable for electromagnetic protection and stealth applications, yet their development is limited by the persistent trade-off between impedance matching and attenuation capability. Although aligned porous architectures have been widely explored to enhance electromagnetic dissipation, most existing strategies rely on unidirectional or single-component alignment and rarely enable the coordinated orientation of magnetic and dielectric phases together with macroscopic impedance grading. Herein, bidirectionally aligned graphene/FeSiAl/polyimide aerogels with coupled micro- and macroscale architectures are fabricated through magnetic-field-assisted directional freezing. At the microscale, a horizontal magnetic field orients ferromagnetic FeSiAl flakes, whereas a vertical temperature gradient directs the alignment of graphene/polyimide cell walls, forming an orthogonally ordered magnetic-dielectric network that promotes conductive loss, interfacial/dipolar polarization, and magnetic dissipation while regulating impedance matching. The optimized single-layer aerogel achieves a maximum effective absorption bandwidth (EAB) of 6.13 GHz at only 1.32 mm, representing a 52.49% improvement over its temperature-gradient-only counterpart, together with a minimum reflection loss (RLmin) of -57.35 dB at 1.74 mm. At the macroscale, layer-by-layer freezing constructs multilayer aerogels, enabling broadband EMW entry and progressive energy dissipation. The optimized multilayer aerogel delivers an ultrabroad EAB of 12.49 GHz and an RLmin of -54.23 dB, yielding a pronounced radar cross-section reduction of 34.08 dB under normal incidence. This multiscale coupling strategy provides an effective route toward lightweight, thin, and broadband EMW absorbers.