Next Generation metasurfaces: tensorial surfaces for novel antenna functionality

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.