三维超材料的电磁双激发协同作用机制与宽带吸波性能

Broadband and strong absorption are the basic requirements of microwave absorbing materials. Since the bandwidths of conventional materials are intrinsically restricted by absorbing mechanism as well as physical limit, the emerging metamaterials have been the most important future direction. Up to now, most existing metamaterials are two-dimensional (2D), which reaches the bottleneck of bandwidth because of the narrow resonance nature originated from the only electric excitation by 2D structures. In this proposal, we expand the concept of metamaterial to three-dimensional (3D), thus both electric and magnetic excitations are possible to be integrated into one metamaterial unit cell, and they can be separately controlled to excite corresponding resonances. This will increase the number of resonances in a certain waveband, broaden absorbing peaks or even cause broadband absorption. We will study the relationships between the 3D structures and absorbing properties, and discuss how to simultaneously enable resonances by both electric and magnetic excitations. On the basis of these theoretical results, broadband absorbing metamaterials with 3D structures will be designed accordingly, then optimized, fabricated and characterized. This proposed project should not only greatly broaden the absorption bandwidth of metamaterials and pave the way of their applications, but also benefit the understanding of absorbing mechanisms of metamaterials. Our researches will provide theoretical and practical directions on how to better control the reflection and absorption of electromagnetic waves by metamaterials.

现有的吸波超材料的结构单元大多数为二维结构，导致只能由入射电磁波的电场产生电激发带来稀疏、窄带的共振吸收。为拓展超材料的吸收带宽，本项目提出采用三维立体结构的超材料单元及其三维空间排布，带来现有二维超材料所不具备的磁激发机制，并且可同时兼具电激发特性，从而增加吸收峰的密度、拓宽吸收峰甚至实现宽带非共振的吸收。通过研究超材料三维结构、排布与电磁波吸收性能之间的关系，分析超材料单元与入射电磁波的相互作用，探讨基于电磁双激发的多重吸收机制的引入和吸收增强，在此基础上设计并优化超材料的三维结构单元和排布。再结合多单元、与传统材料复合等手段，获得具有宽带强吸收和高带宽厚度比的三维超材料，通过三维雕刻与3D打印技术进行制备。本项目不但能极大地拓展吸波超材料的带宽，推动其应用；同时也将加深对超材料本身及其吸波机制的认识，为更好地利用超材料控制电磁波的反射、吸收行为提供理论和实验依据。

近年来新型吸波超材料受到广泛关注，然而单一的吸收机制及平面内有限的超材料结构设计空间导致了窄带的共振吸收局限。为拓展超材料的吸收带宽，本项目围绕三维立体结构的超材料及其电磁双激发的多吸波机制及基于该机制的宽带吸波材料设计开展研究。项目探寻超材料三维结构、排布与电磁波吸收性能之间的关系，通过分析超材料单元与入射电磁波的相互作用，引入基于电磁双激发的多重吸收机制；结合多单元、与传统材料复合等手段，获得具有宽带强吸收的三维超材料，并制备及测试验证，最终形成基于多机理复合的宽带吸波三维超材料设计方法。项目研究取得的主要成果有：1）通过对立式超材料进行场分析，发现对于立体放置的超材料单元能够在电磁波的激发下同时产生电共振和磁共振，同时反射背板带来的多重反射进一步拓展了吸收带宽，增加了吸收强度。基于此，采用立体放置的闭口谐振环（CRRs），在5.6 - 19和22 - 26.6 GHz的频段内实现了85%的吸收。2）建立了将超材料单元进行层间复合，以及将超材料三维结构与传统磁性材料相复合的方法，可以得到介电、电阻、磁共振、电共振、电磁散射等多个机制协同作用的复合吸波超材料。3）基于三维结构超材料及多吸波机理复合机制，设计并制备了具有λ/20以下的小尺度共振单元及低频吸波性能的多层吸波超材料、在室温-1000℃具有稳定吸波性能的耐温吸波超材料、具有跨越工频-6 GHz可调谐吸收峰位的吸波超材料、以及在5~34 GHz之间具有超宽带隐身性能的复合吸波超材料。本项目不但能极大地拓展吸波超材料的带宽，推动其应用；同时也将加深对超材料本身及其吸波机制的认识，为更好地利用超材料控制电磁波的反射、吸收行为提供理论和实验依据。