东南大学崔铁军团队研究了宽带色散工程中电磁超表面的二阶德拜弛豫。相关论文发表在2025年3月27日出版的《光：科学与应用》杂志上。

在介电物理学中，电介质的电磁（EM）特性源于几个重要的极化机制，这些机制可以用德拜、德鲁德或洛伦兹模型来描述。超材料及其二维对应的超表面可以表现出奇异的电磁参数，如负介电常数，而导致这种现象的极化机制在介电物理学中早已被讨论过。德鲁德和洛伦兹模型通常用于超材料设计，而德拜模型几乎不存在，尽管它在介电物理学中非常重要。

这在介电物理学和超材料之间留下了不可调和的差距。研究组从宽带色散工程的角度探讨了元表面中的德拜弛豫。通过分析典型元原子的两个基本共振模式，他们首先表明，尽管其通常是洛伦兹共振，但反射相位在两个共振下会经历一阶德拜弛弛豫。更重要的是，这两个共振可以被定制以形成二阶德拜弛豫过程，从而在它们之间实现平滑的相位变化，这为宽带色散工程奠定了坚实的基础。

作为概念证明，研究组提出了一种四椭圆弧（QEA）结构作为元原子，其色散可以通过定制二阶德拜弛豫来定制。通过这个元原子，他们展示了两个元表面原型，它们可以在整个X波段（8.0-12.0 GHz）分别实现彩色和非彩色聚焦，展示了宽带色散工程的强大能力。这项工作挖掘了超材料中的弛豫过程，为超材料研究开辟了新的领域，这可能会在宽带设备和系统中得到广泛应用。

附：英文原文

Title: 2nd-Order Debye relaxation in electromagnetic metasurfaces for wideband dispersion engineering

Author: Fu, Xinmin, Han, Yajuan, Wang, Jiafu, Yang, Jie, Sun, Yong, Ding, Chang, Jia, Yuxiang, Wang, Jun, Qu, Shaobo, Cui, Tiejun

Issue&Volume: 2025-03-27

Abstract: In dielectric physics, electromagnetic (EM) properties of dielectrics arise from several important polarization mechanisms that can be described by Debye, Drude or Lorentz models. Metamaterials, as well as their 2D counterparts-metasurfaces, can exhibit bizarre EM parameters such as negative permittivity, whereas polarization mechanisms leading to such have long been discussed in dielectric physics. Drude and Lorentz's models are usually used in metamaterial design, whereas the Debye model is almost absent, though it is so important in dielectric physics. This leaves an unreconciled gap between the dielectric physics and metamaterials. In this paper, we explore Debye relaxations in metasurfaces for the sake of wideband dispersion engineering. By analyzing two fundamental resonance modes of a typical meta-atom, we first show that the reflection phase experiences 1st-order Debye relaxation under the two resonances, although they are typically Lorentzian. More importantly, the two resonances can be tailored to form a 2nd-order Debye relaxation process so as to achieve smooth phase variations in between them, which lays a solid foundation for wideband dispersion engineering. As proof of concept, we propose a quad-elliptical-arc (QEA) structure as the meta-atom, whose dispersion can be customized by tailoring the 2nd-order Debye relaxation. With this meta-atom, we demonstrated two metasurface prototypes that can achieve chromatic and achromatic focusing, respectively, in the entire X band (8.0–12.0GHz), showcasing the powerful capacity of wideband dispersion engineering. This work digs out relaxation processes in metamaterials and opens up new territories for metamaterial research, which may find wide applications in wideband devices and systems.

DOI: 10.1038/s41377-025-01813-1

Source: https://www.nature.com/articles/s41377-025-01813-1