基于科赫分形的新型超材料双频吸收器

摘要

本文提出了一种基于科赫(Koch)分形结构的新型超材料双频吸收器，其由二阶科赫分形阵列、介质层和金属背板三部分组成.通过利用分形结构的空间填充性，其单元尺寸在相同吸收频率下相对于具有正方形谐振结构的传统吸收器有近17.5%的尺寸缩减.与传统实现多频工作的组合法、层叠法不同，该型吸收器的双频特性来源于科赫分形曲线在电磁波激励下呈现出的两种不同的谐振模式.而且由于结构上具有旋转对称性，该型吸收器对入射波的极化方向不敏感，在横电波、横磁波大角度入射时仍能保持较高的吸收率.文中采用等效介质理论对该型吸收器进行了分析，测量结果与仿真结果取得了较好的一致性.%In this paper we present a novel dual-band metamaterial absorber (MA), which is composed of a periodically arranged 2nd order Koch curve array and a metal ground separated by a dielectric spacer. By employing the fractal characteristic of space-filling, more compact unit cell with a size reduction of 17.5%has been achieved as compared with the conventional square-shaped MA. The dual-band operation is not originated from the hybrid or stacked methods as reported before, but from the two distinct resonance modes of the 2nd order Koch curves induced by the incident electromagnetic wave, and can be realized within a single unit cell. Due to its rotationally symmetric pattern, the absorptivity of the above presented MA is insensitive to the polarization of the incident waves and can perform well in a wide range of incident angles. The effective medium theory has been employed to investigate the underlying physical mechanism of the fractal MA, and good agreements between simulation and experimental results have been achieved.