人工电磁表面对微波波段电磁波的高效人工调控：机理与应用

In this research, the metasurface based on phase discontinuity will be proposed to realize the wavefront control and manipulation with the ultrathin thickness in the propagation direction. Since the the gradual phase changes accumulated along the transmission path in conventional lens are taken placed by the abrupt phase change at the interface, the metasurfaces provide an alternative approach to wave control, thickness reduction, simplify the fabrication. First, we will propose the design method for sub-wavelength unit cells with desird responses of phase and amplitude. Second, in order to enhance the efficieny and the bandwidth of the ultra-thin lenses, the effective medium and equivalent circuit of the unit cells will be put forward, as the means to study the electromagnetic responses of the unit cells. Then, the the impedance mathcing, the coupling efficieny and the magnetic resonance between the unit cells will be discussed to achieve the efficient and broadband performance fo the unit cell. The local periodicity approximation will by proposed to achieve the ultrathin efficient metassurface when the adrupt phase changes are introduced. Third, we will design the untrathin metasurface in microwave region to realize the high efficiency wavefront manipulation, ultrathin cloak and antenna array without the feed network. Our research will make great improvements in efficiency, thickness reduction and fabrication simplification. It will overcome several challenges of earlier metasurface designs, providing a promising route to miniaturize, planarize and integrate multiple microwave components, and will be a promising application in the next generation communication system and the smart skin.

针对微波波段现有电磁波调控器件所存在的尺寸极限及其对电磁波极为有限的调控能力，依据本项目组前期已获得的研究成果凝练出若干科学问题，提出利用分界面上的相位突变机制替代电磁波在传播路径上的相位累积，构造出微波波段人工电磁表面，实现亚波长尺度上电磁波的深度调控。首先，提出具有特定相位突变及幅度响应的单元设计方法；其次，通过单元耦合、阻抗匹配及引入磁响应等途径，提高单元结构的工作效率、拓宽工作频带，并探索近似周期边界条件在高效人工电磁表面设计中的应用；第三，利用人工电磁表面在深度亚波长尺度上对电磁波的调控能力，构造微波波段的超薄透镜，实现电磁波的高效传播调控，并将其用于超薄隐身衣及馈电网络自由化的天线阵列。本研究从物理机制、实验验证和应用基础三大方面全方位展开工作，将极大程度上减小微波波段电磁波调控器件的厚度及重量，促进与其他组件的集成化和实用化，为其在未来通信系统、智能蒙皮中的应用奠定基础。

近年来，随着电磁波在探测定位、能源利用、光学通信等领域的广泛应用，在整个频域范围内对电磁波进行精确的人工调控已逐步成为电磁领域最热门的研究方向之一。调控电磁波的传统方法是利用三维的波束调控器件，通过在传播过程中累积产生的相位差对电磁波的传播状态进行控制。由于这些光学器件均由现有的介质材料产生，普遍体积较大，外形不统一，难以实现平面化，加大了在系统中与其他器件集成的难度。而超表面(metasurface)的出现能够完美的解决这一问题，通过对材料结构和尺寸的有序设计来获得超常于自然界中固有的物理特性，能够有效实现满足人为意愿的电磁波调控，具有十分广阔的应用前景。本研究在四年的时间里，针对微波段超表面对电磁波波前调控的理论研究及应用展开了相关研究。首先从单层超表面出发，推导了单层透射型超表面的交叉极化转化效率的极限值，设计了具有汇聚波前的单层超构透镜。其次，通过建立多层超单元的理论模型，为高效多功能的超透镜设计提供了理论依据和设计基础。通过几何相位原理，设计了能够高效激发微波段透射型涡旋波束的超透镜。进一步地将传输相位与几何相位相结合，提出了一种能够对正交圆极化状态解耦合的普适方案，通过设计双层，以及多层超透镜，分别实现了对正交圆极化波束的独立波前调控。最后，利用超表面实现了微波波段的全息成像。这些研究成果为电磁波调控器件平面化提供了有效的理论依据。