As wireless communication, radar imaging, and electronic systems advance toward millimeter-wave and terahertz frequencies, electromagnetic compatibility (EMC) increasingly requires absorbers that combine broadband attenuation, strong absorption, thin profiles, and complex device-compatible architectures. Researchers from the University of Electronic Science and Technology of China, led by Professors Xiao Sun, Feng Lan, Yaxin Zhang, and Qiye Wen, developed a rheologically engineered direct ink writing (DIW) 3D-printing strategy for highly loaded graphene/carbonyl iron (Gr/CIP) composites. By quantitatively connecting ink rheology with printing fidelity and electromagnetic performance, the team fabricated gradient honeycomb absorbers capable of ultra-broadband attenuation and direct device integration.
Why This Absorber Matters
Conventional electromagnetic absorbers often provide effective attenuation over limited frequency ranges, while increasing magnetic filler loading can dramatically increase viscosity, aggregation, and structural instability, compromising printability. The researchers therefore targeted the combined challenge of high filler loading, printable rheology, and precise three-dimensional fabrication, rather than optimizing electromagnetic composition alone.
Innovative Design and Mechanism
Graphene serves a dual role as an electromagnetic-loss component and rheological network regulator in the Gr/CIP-PDMS ink. Graphene sheets form a supporting network around carbonyl iron particles, enabling shear-thinning behavior, sufficient yield stress, and rapid structural recovery while introducing conductive and interfacial polarization losses. The optimized formulation reaches approximately 84.06 wt% CIP loading, with viscosity recovery exceeding 95% within 180 s, allowing printed filaments to retain their designed geometry. A gradient honeycomb structure, with apertures gradually varying from ~2.6 to 4.6 mm, further improves impedance matching and extends electromagnetic propagation through repeated scattering and refraction. Meanwhile, graphene, carbonyl iron, and Gr/CIP/PDMS interfaces provide synergistic dielectric, magnetic, and Maxwell–Wagner polarization losses.
Outstanding Performance
The resulting gradient honeycomb absorber achieves broadband absorption from 18 GHz to 4 THz with reflection loss (RL) ≤ −10 dB. The optimized H2 structure reaches an RLmin of −84.30 dB in the terahertz range, with an average RL below −35.2 dB at only 2.6 mm thickness. A printed matching layer extends low-frequency absorption, enabling continuous coverage across 18 GHz–4 THz with a maximum thickness of 4.25 mm and average RL of −31.4 dB. The structure also withstands six months of air exposure, 168 h at 85 °C/85% RH, and 200 bending cycles while maintaining stable absorption performance.
Applications and Future Outlook
The absorber demonstrates direct device-level integration with terahertz reconfigurable intelligent surfaces (RIS). Conformal 3D printing suppresses parasitic reflections and edge scattering, increasing average main-lobe gain by approximately 3.3 dBi to ~16 dBi, while reducing specular-reflection beamwidth by ~58% to 3°. In 120 GHz radar imaging, it suppresses scattering around aircraft-model edges, while simulations show radar cross-section reductions of up to 21.4 dBsm at 30 GHz. Overall, the rheology–printing–structure–electromagnetic design framework provides a scalable route toward advanced EMC solutions for 6G/THz communications, radar imaging, electromagnetic scattering suppression, and stealth technologies.
Nano-Micro Letters
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