Next Generation metasurfaces: tensorial surfaces for novel antenna functionality

本项目的重点是设计、建模、制造和表征表现出张量表面阻抗的2D超表面，或表面3D超材料或复合材料。结合适当的天线设计，这些发现将支持未来的民用应用，如物联网、用于筛查的高频成像系统、用于医疗诊断和无线测量的扫描仪和层析系统以及智能仪表系统。为了引导和辐射电磁波，沿标量阻抗表面的能量传播已经研究了一段时间。已经探索了一维和二维人工阻抗表面来控制导波和漏波辐射。事实上，‘Sivenpiper-蘑菇’阵列[1]可能是最著名的超表面，埃克塞特的研究人员已经成功地使用了基于此的非均匀设计来制造和实验测试表面波伦堡透镜装置[2]。类似的结构表面也可以用来降低天线系统的高度。这是因为，在它们的共振频率下，表面阻止了表面波的传播，并呈现出磁导体边界条件。与理想的电导体不同，具有这种磁边界条件的材料在自然界中是不存在的：它迫使磁通量的切向分量和电场的法向分量为零。通过这种方式，辐射元件可以被放置在离地面非常近的地方，而不会受到由简单的金属接地平面引起的图像源所产生的干扰的有害影响。本项目使我们的理解超越了当前的技术水平[3-6]，并且以探索将天线特征模耦合到非均匀和张量阻抗表面为中心。这些超表面可以是印刷电路板类型的超表面，也可以是“大块”超材料或磁性复合材料的表面。首先，我们将努力了解可以探索的参数空间的范围(根据边界条件)。下一步是在这些表面附近放置一个简单的偶极子源，以了解它们如何影响源的辐射特性。反过来，我们将考虑如何提高更复杂的天线的效率、功能或方向性，以及如何缩小尺寸或厚度，以及辐射波束的极化。由此产生的结构轻巧、潜在的共形和紧凑的体积，对航空航天和空间应用特别有价值。挑战众多且困难，但我们期待有能力的研究人员在基础理解和设备设计方面取得巨大进步。在科学文献中有大量的研究，研究人员将被要求进行实质性的审查，以向赞助商提供关于超表面和复合材料的最新研究成果的摘要。他或她将需要熟悉各向异性、层状和磁性材料的物理学，以及波动光学的基本原理和复杂性。该项目将包括分析、建模、制造和实验元素，学生将被期望与其他在相关领域工作的研究人员密切互动。

It is the focus of this project to design, model, fabricate and characterise 2D metasurfaces, or the surface 3D metamaterials or composites, that demonstrate a tensorial surface impedance. When combined with appropriate antenna designs, the findings will support future civil applications like the internet of things, high frequency imaging systems for screening, scanners and tomography systems for medical diagnostics and wireless measurement and smart meter systems.Propagation of energy along scalar impedance surfaces for the purpose of guiding and radiating electromagnetic waves has been studied for some time. Both 1-D and 2-D artificial impedance surfaces have been explored to control guided waves and leaky-wave radiation. Indeed the 'Sievenpiper-mushroom' array [1] is perhaps the best known metasurface, and Exeter researchers have successfully used an inhomogeneous design based on this to fabricate and experimentally test a surface-wave Luneburg lens device [2]. Similar structured surfaces can also be employed to reduce the height of antenna systems. This is because, at their resonant frequency, the surface forbids the propagation of surface waves, and presents a magnetic-conductor boundary condition. Unlike perfect electric conductors, materials with this magnetic boundary condition do not exist in nature: it forces the tangential components of magnetic fluxes and the normal components of electric fields to be zero. In this way radiating elements can be placed very close to the surface without the detrimental effects associated with the interference created by images sources induced by a simple metal ground plane.This project takes our understanding beyond the current state-of-the art [3-6], and is centred around an exploration of coupling antenna eignenmodes to inhomogeneous and tensorial impedance surfaces. These metasurfaces can be those of the printed-circuit-board-type, or the surface of 'bulk' metamaterials or magnetic composites. Initially we will work to understand the extent of the parameter space (in terms of the boundary conditions) that can be explored. The next step is then to place a simple dipole source close to these surfaces to understand how they can influence the source's radiation characteristics. In turn, we will consider how the efficiency, functionality or directivity of more complex antenna can be improved, as well as reduction of size or thickness, and the polarisation of the radiated beam. A resulting structure that is lightweight, potentially conformal, and with compact volume, is particularly valuable to aerospace and space applications.The challenges are numerous and difficult, but we expect great advances in fundamental understanding and device design from a competent researcher. There are a wealth of studies in the scientific literature, and the researcher will be required to undertake a substantial review to provide the sponsors with a summary of the state-of-the-art on metasurfaces, and composite materials. He or she will need to become familiar with the physics of anisotropic, layered and magnetic materials, and the fundamentals and complexities of wave optics. The project will include analytical, modelling, fabrication and experimental elements, and the student will be expected to interact closely with other researchers working in related areas.