In this work, we propose a novel broadband terahertz (THz) metamaterial absorber (MMA) based on double-spiral structures, including discrete and continuous ones. The gradient ring resonators are in a discrete spiral topological distribution to expand the absorption band. By stacking two layers with a certain proportion, the proposed THz MMA can further enhance the energy loss to achieve absorption over 0.9 for TE mode at 2.57–5.19 THz and TM mode at 2.43–5.6 THz, with relative absorption bandwidths (RABWs) of 67.5% and 81.7%, respectively. Meanwhile, the polarization-insensitive bandwidth is 2.57–5.19 THz, with RABW of 67.5%. In addition, the normalized impedance for both modes is investigated. Furthermore, according to the analysis of the distributions of the surface current and electric field, it is clear that the electromagnetic energy loss mainly originates from the electric and magnetic resonances induced by the interaction between the metal resonators. To a certain extent, the Fabry–Perot resonance existing between the dielectric layers also contributes to the improvement of the absorption. This THz MMA, based on a unique double-spiral arrangement, can be used in many fields owing to its ultra-broad absorption band and polarization-insensitive characteristic in a broad band.

中文翻译：

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基于离散螺旋拓扑分布的带梯度环谐振器的宽带太赫兹吸收器

在这项工作中，我们提出了一种基于双螺旋结构的新型宽带太赫兹（THz）超材料吸收器（MMA），包括离散和连续的结构。梯度环谐振器呈离散的螺旋拓扑分布，以扩展吸收带。通过以一定比例堆叠两层，拟议的THz MMA可以进一步提高能量损耗，以实现TE模式在2.57–5.19 THz和TM模式在2.43–5.6 THz处的吸收超过0.9，相对吸收带宽（RABW）为67.5 ％和81.7％。同时，对极化不敏感的带宽为2.57–5.19 THz，RABW为67.5％。此外，还研究了两种模式的归一化阻抗。此外，根据对表面电流和电场分布的分析，显然，电磁能的损失主要源于金属谐振器之间相互作用引起的电和磁共振。在一定程度上，电介质层之间存在的Fabry-Perot共振也有助于吸收的改善。该THz MMA基于独特的双螺旋排列，由于其超宽的吸收带和宽带的对极化不敏感的特性，可在许多领域中使用。