电磁波在三维石墨烯立体结构中的传输特性与衰减机制研究

The demand of military stealth technology and the increasingly serious electromagnetic pollution have provided an opportunity for the research and development of electromagnetic wave absorbing materials. Designing and regulating the transmission path of electromagnetic wave and probing into the energy attenuation mechanism are the emphasis and difficulty of the research of stealth materials. The propagation rule and attenuation mechanism of electromagnetic wave in the three-dimensional(3D) structure of graphene will be studied because the 3D graphene composites exhibit significantly enhanced microwave absorption properties compared with 2D graphene. The self-assembly mechanism of 3D graphene will be explored to realize the controllable fabrication of 3D graphene and its composites. The molecular structure and pore model of 3D graphene are constructed to illustrate the reflection, refraction and scattering rules of electromagnetic wave entering into 3D structure. The conductive mechanism of 3D graphene is revealed, and the formation of conductive network in composites and the influence of relaxation interface on electromagnetic wave response behavior are studied. Based on the above discussion, the equation among molecular structure, pore structure and equivalent electromagnetic parameters of composites is established. A reasonable microwave absorbing model is expected to explain the controllable preparation and microwave loss mechanism of 3D graphene and its composites, which contains the microwave absorption properties, the intrinsic dielectric properties and the geometric features of 3D graphene. The research will provide reliable theoretical foundation and technical support to the existing research on the theory of design and the preparation of microwave absorbing materials, which has considerable significance to the research on the microwave absorbing materials with wider frequency range and higher efficiency of microwave absorption.

军事隐身技术的需求和电磁污染的日益严重为吸波材料的研究和发展提供了机遇。设计和调控电磁波传输路径并深入探究其衰减机制是隐身材料研究的重点和难点。本项目基于石墨烯从二维转变为三维立体结构后能有效提高吸波特性的现象，开展电磁波在特殊三维立体结构中的传播规律与衰减机制研究。探明二维石墨烯转变成复杂三维立体结构过程中的自组装机制，可控制备三维石墨烯及其复合材料。构建三维石墨烯分子结构与孔隙模型，阐明电磁波在三维立体结构中反射、折射与散射的传播规律，揭示三维石墨烯的导电机制，研究复合材料中导电网络的形成以及弛豫界面的数量对电磁波响应行为的影响规律，建立分子结构、孔隙结构与复合材料等效电磁参数的关系式。从三维石墨烯微观结构的本征介电性质及其结构特征两个层面阐明电磁波的多重衰减机理，建立三维石墨烯吸波复合材料的材料特性-结构特征-微波吸收之间的关联，为实现材料对电磁波的宽频带、高效率吸收奠定理论基础。

军事隐身技术的迫切需求和电磁污染的日益严重对吸波材料的研究和发展提出了新要求。石墨烯气凝胶具有连续三维网络立体结构，拥有超大的比表面积、优异的导电导热性能，在电磁屏蔽与吸波材料领域有着广泛的应用前景。为了探明电磁波在三维多孔结构中的传输特性与衰减机制，本项目执行期间开展了以下工作：1、采用还原自组装法制备了超轻可压缩石墨烯气凝胶，考察了工艺参数对石墨烯气凝胶形貌、结构、组成及性能的影响。以氧化石墨烯溶液为前驱体，L-抗坏血酸为还原剂，经优化还原及冷冻干燥工艺，得到密度为5.26mg/cm3、200g负载下体积压缩为80.43%的超轻可压缩石墨烯气凝胶。石墨烯气凝胶独特的结构形成主要在于氨水提供的含氮化学键增大了石墨烯片层间的斥力所致。2、研究了不同工艺条件下石墨烯气凝胶的电磁性能，当反应温度为180℃，质量分数为5%，厚度为4mm的石墨烯气凝胶/石蜡复合材料具备较优吸波性能，小于-5dB和-10dB的有效带宽分别达7.2GHz和1.76GHz，且存在有双吸收峰，反射系数最大可达-11.17dB。石墨烯气凝胶复合材料的电磁波吸收机制来源于石墨烯多孔结构对电磁波的多重反射、内部缺陷和杂质形成的偶极子所引起的散射作用。3、根据石墨烯气凝胶的孔隙结构，设计了周期空心圆台、瓦楞、方孔、多孔渐变等宽频吸波结构，采用仿真方法研究了结构参数、方阻等结构特性与材料特性对微波吸收性能的影响。结果表明：25mm时空心圆台结构小于-10dB的带宽达到16.31GHz。瓦楞厚度为18mm时，小于-10dB的有效吸收带宽在1-18GHz的频段下达到15.69GHz，并且在3.75GHz达到最大吸收峰值-25.93dB。多孔渐变吸波结构表面电阻为800Ω/sq时，低于-10dB的带宽达到15.89GHz。4、吸波材料结构设计与材料特性的协同作用是实现吸波材料宽频隐身的一种有效途径。多孔结构吸波材料的吸波性能主要来源其三维结构几何尺寸和表面方阻的调控，可改善材料与空气的阻抗匹配，并通过形成表面电流将电磁能转化为热能，大量衰减进入材料内部的电磁波。项目研究结果将为阐明电磁波与物质的相互作用及研制宽频吸波材料提供一定参考价值。