The theory of space-time varying metamaterials (Ref. 4659)

时空变化超材料理论 (参考文献 4659)

• 批准号: 2859646
• 金额: --
• 依托单位: UNIVERSITY OF EXETER
• 依托单位国家: 英国
• 项目类别: Studentship
• 财政年份: 2023
• 资助国家: 英国
• 起止时间: 2023 至 无数据
• 项目状态: 未结题
• 来源: https://gtr.ukri.org/projects?ref=studentship-2859646
• 关键词: theory; space; time; varying; metamaterials

When we first learn about wave propagation we are taught about the refractive index, n. This is first simply a number; about 1.5 for glass, and a large complex number for metals. Next we learn the refractive index can depend on position. The spatial dependence of the refractive index leads to reflection, where the wave vector changes sign, one of the most everyday of wave phenomena. Metamaterial research is commonly concerned with designing sub-wavelength scale structures with an effective refractive index that can be varied across space in a controlled way.But what about a refractive index that varies in time? An example could be where n is the same throughout space, but at some moment in time its value changes. Again there is reflection, but unlike reflection from a spatial interface, the reflected wave occurs after it encounters the temporal 'interface', as required by causality [1]. In this case the frequency changes sign rather than the wave vector. Varying the refractive index in time we thus alter the frequency (e.g. colour, in the case of visible light) of the wave. If we change the refractive index in both space and time we then have the ability to change the wave in a way that would be otherwise impossible, modifying both its frequency and direction of propagation. Space-time varying material parameters have been shown to lead to extreme wave amplification without requiring gain [2], and laboratory analogues of astrophysical phenomena such as Hawking radiation [3].However, until recently it has been challenging to make materials where the parameters vary in time. Recent experiment in optics [4] and acoustics [5] have made time varying material parameters a reality. Yet these materials typically have a complicated effect on an incident wave, that is a far cry from the simplified picture described above. Not only is the refractive index not changed instantaneously, but it also depends on frequency. At present there is no agreed theoretical approach to the calculation of fields within these materials. This project will develop the theory of space time varying metamaterials, building on the theoretical approach derived in [6] where the material parameters are replaced with operators.In this project we will:(1) Investigate the physics of space time varying metamaterials, considering a variety of experimental platforms, from acoustics, to optics, and radio frequency materials.(2) Further develop the theory in [6], treating non-planar materials, non-electromagnetic waves, and more exotic material parameters, e.g. anisotropy or bianisotropy. Attempt to develop analytical solutions to these operator equations that have so far been treated only numerically.(3) Apply the theory to understand how the effects reported in e.g. [1,2] change when moving from theoretical idealizations to more realistic experimental platforms.(4) Use the theory to explore new and unforeseen wave phenomena in space-time varying metamaterials.References:[1] E. Galiffi, R. Tirole, S. Yin, H. Li, S. Vezzoli, P. A. Huidobro, M. G. Silveirinha, R. Sapienza, A. Alu, and J. B. Pendry "Photonics of Time-Varying Media" Adv. Phot. 4, 014002 (2022).[2] J. B. Pendry, E. Galiffi, and P. A. Huidobro, "Gain mechanism in time-dependent media", Optica 8, 636-637 (2021).[3] R. Anguero-Santacruz and D. Bermudez, "Hawking radiation in optics and beyond", Phil. Trans. Roy. Soc. A 378, https://doi.org/10.1098/rsta.2019.0223 (2020).[4] J. Bohn, T. S. Luk, C. Tollerton, S. W. Hutchings, I. Brener, S. A. R. Horsley, W. L. Barnes, and E. Hendry, "All-optical switching of an epsilon-near-zero plasmon resonance in indium tin oxide", Nat Commun. 15 1017 (2021).[5] C. Cho, X. Wen, N. Park, et al. "Digitally virtualized atoms for acoustic metamaterials" Nat. Commun. 11, 251 (2020).[6] S. A. R. Horsley, E. Galiffi, and Y. T. Wang, "Eigenpulses of dispersive time-varying media" arXiv:2208.11778 (2022).

当我们第一次学习波传播时，我们学到了折射率 n。首先，这只是一个数字；对于玻璃来说大约是 1.5，对于金属来说是一个很大的复数。接下来我们了解到折射率可能取决于位置。折射率的空间依赖性导致反射，其中波矢量改变符号，这是最常见的波动现象之一。超材料研究通常关注设计亚波长尺度结构，其有效折射率可以以受控方式在空间上变化。但是随时间变化的折射率又如何呢？一个例子是 n 在整个空间中是相同的，但在某个时刻它的值会发生变化。再次存在反射，但与空间界面的反射不同，反射波在遇到时间“界面”后发生，根据因果关系 [1]。在这种情况下，频率改变符号而不是波矢量。随着时间的推移改变折射率，我们就改变了波的频率（例如，在可见光的情况下的颜色）。如果我们改变空间和时间上的折射率，那么我们就有能力以一种原本不可能的方式改变波，改变它的频率和传播方向。时空变化的材料参数已被证明可以在不需要增益的情况下导致极端的波放大[2]，以及霍金辐射等天体物理现象的实验室模拟[3]。然而，直到最近，制造参数满足以下条件的材料仍然具有挑战性随时间变化。最近的光学 [4] 和声学 [5] 实验已经使随时间变化的材料参数成为现实。然而，这些材料通常会对入射波产生复杂的影响，这与上述的简化图像相去甚远。折射率不仅不会瞬时改变，而且还取决于频率。目前，还没有一致同意的理论方法来计算这些材料中的场。该项目将发展时空变超材料理论，建立在[6]中导出的理论方法的基础上，其中材料参数被运算符替换。在该项目中，我们将：（1）研究时空变超材料的物理特性，考虑各种实验平台，从声学、光学到射频材料。(2) 进一步发展[6]中的理论，处理非平面材料、非电磁波和更奇特的材料参数，例如各向异性或双各向异性。尝试为这些迄今为止仅以数值方式处理的算子方程开发解析解。(3) 应用该理论来理解如何报告影响，例如： [1,2]从理论理想化转向更现实的实验平台时发生的变化。(4)利用理论探索时空变化超材料中新的和不可预见的波动现象。参考文献：[1] E. Galiffi，R. Tirole， S. Yin、H. Li、S. Vezzoli、P. A. Huidobro、M. G. Silveirinha、R. Sapienza、A. Alu 和 J. B. Pendry “时变介质的光子学”Adv。照片。 4、014002(2022).[2] J. B. Pendry、E. Galiffi 和 P. A. Huidobro，“时间依赖性介质中的增益机制”，Optica 8, 636-637 (2021)。[3] R. Anguero-Santacruz 和 D. Bermudez，“光学及其他领域的霍金辐射”，Phil。跨。罗伊.苏克。 A 378，https://doi.org/10.1098/rsta.2019.0223（2020）。[4] J. Bohn、T. S. Luk、C. Tollerton、S. W. Hutchings、I. Brener、S. A. R. Horsley、W. L. Barnes 和 E. Hendry，“氧化铟锡中ε-近零等离子体共振的全光开关”，Nat交流。 15 1017 (2021).[5] C. Cho、X. Wen、N. Park 等。 “用于声学超材料的数字虚拟化原子”Nat。交流。 11, 251 (2020).[6] S. A. R. Horsley、E. Galiffi 和 Y. T. Wang，“色散时变介质的特征脉冲”arXiv:2208.11778 (2022)。