1成果简介

 

        对轻质电磁波（EMW）吸收单体的需求日益增长，尤其是那些能够同时吸收低频和宽带电磁波的材料，这带来了重大挑战。尽管介电纳米结构气凝胶展现出巨大潜力并取得进展，但在开发基于气凝胶的电磁波吸收体以实现有效低频和宽带吸收方面仍存在差距。本文，山东大学刘久荣 教授、吴娜 研究员、曾志辉 教授、东北大学王莅辰 副教授等在《ADVANCED FUNCTIONAL MATERIALS》期刊发表名为“Ultrabroadband Low-Frequency Microwave Absorption in Multiscale Aerogel-Metamaterial Hybrids”的论文，研提出一种多尺度工程策略，用于制造气凝胶-超材料混合体，从而解决宽带宽、低频吸收和高承载能力等关键难题。该吸收体由模拟辅助增材制造的薄壁外壳构成，其内部嵌入石墨烯/纳米纤维素气凝胶，形成高效导电网络并具备丰富异质界面。
        该多尺度设计使吸收体在2-18 GHz全频段展现卓越的电磁波吸收性能，实现100%带宽覆盖，并在宽斜入射角（达60°）及双极化（横电波与横磁波）条件下保持稳定性能。此外，该吸收体展现出2.714 kg m?2的低面积密度，并能承受至少95 kg的平面外载荷。这些突破性进展凸显了开发轻质新型电磁波吸收气凝胶超材料的潜力，可应用于低频超宽带电磁兼容性及航空航天领域。
        2图文导读 

 

       图1、Multiscale engineering of graphene/CNF aerogel-metamaterial hybrids for ultrabroadband low-frequency EMW absorption. (a) Digitally-driven geometric optimization of macroscopic metastructure. (b) Photograph of graphene/CNF aerogel-metamaterial hybrids. (c) Microstructural engineering of graphene/CNF aerogels. (d) Photograph of the graphene/CNF aerogel-metamaterial hybrids sustaining a person weighing 95 kg. (e) Comparison of EAB of our aerogel-metamaterial hybrids with previously reported EMW absorbing aerogels.

 

        图2、Structure and properties of graphene/CNF aerogel and aerogel-metamaterial hybrids. (a) Photograph of graphene/CNF aerogel standing on foxtail grass (inset show a photograph of the aerogel sustaining an item weighing >1000 times heavier). (b) SEM image and pore size distribution of graphene/CNF aerogel. (c) SEM images of the fracture surface of graphene/CNF aerogel pore walls. (d) Schematic diagram of “graphene-CNF” interface polarization. (e) Differential charge density of “graphene-CNF” interface. (f) Profile of charge density of “graphene-CNF” interface. (g) Out-of-plane compression force-displacement curve of graphene/CNF aerogel-metamaterial hybrids. (h) Photograph of out-of-plane compression failure region. (i) Contours of von Mises stress distribution in the shell and graphene/CNF aerogel under out-of-plane compression.

 

        图3、Electromagnetic properties and EMW absorption performance of graphene/CNF aerogel. (a) Permittivity of graphene/CNF aerogel with different CNF contents at the density of 40 mg/cm3. (b) Permittivity of graphene/CNF aerogel with 20 wt.% CNF at different densities. (c) The polarization (εp″) and conductive (εc″) losses of graphene/CNF aerogel. (d–f) EMW absorption performance of graphene/CNF aerogel with 20 wt.% CNF at different densities. (g–i) EAB of graphene/CNF aerogel with 20 wt.% CNF at different densities.

 

 　　图4、EMW absorption performance of graphene/CNF aerogel-metamaterial hybrids. (a) Test systems of graphene/CNF aerogel-metamaterial hybrids. (b) Photograph of the experimental testing scenarios. (c–g) RL of graphene/CNF aerogel-metamaterial hybrids at different polarization modes and various oblique incidence angles. (h) Comparison of EMW absorption performances regarding the minimal reflection loss (RLmin) and EAB of typical EMW absorbing materials.

 

        图5、Power loss distribution, complex electric field, and magnetic field intensity time-averaged amplitude distribution (2D and 3D) at typical frequencies. (a) 3.87 GHz. (b) 6.16 GHz. (c) 9.47 GHz. (d) 13.39 GHz. 1′-1′ and 2′-2′ indicate the corresponding cross sections.

 

        图6、The EMW absorption mechanisms of graphene/CNF aerogel-metamaterial hybrids. (a) EMW absorption mechanisms at macroscopic scale. (b) EMW absorption mechanisms at mesoscopic scale. (c) EMW absorption mechanisms at microscopic scale.
        3小结
        本文提出一种电磁波吸收体设计方案，该方案利用二维石墨烯与一维碳纳米纤维强烈的导电/极化耦合损耗机制，并结合具有梯度阻抗匹配特性的三维气凝胶超材料。受限于固有阻抗匹配问题，现有电磁波吸收体主要在中高频段展现出优异吸收性能，导致S波段吸收成为难题。本方案通过新型气凝胶-超材料复合体的多尺度工程策略突破该局限，显著拓宽吸收带宽。所得纳米结构气凝胶-超材料复合体在2至18 GHz频段实现近乎完美吸收，实现兼具低频兼容性的超宽带电磁波吸收。此外，该复合材料的面积密度仅为2.714千克每平方米，低于现有超材料。该开发在无人机外壳领域具有巨大潜力，该领域既需重量敏感性，也需具备结构承载能力。
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