| dc.description.abstract | The ability to manipulate electromagnetic radiation is key to a huge range of current technologies, from communications and sensing to cooking and energy generation. It is expected that improving our ability to manipulate radiation in new ways will lead to many new technologies, such as invisibility cloaks and optical computing. One way to advance our ability to shape the electromagnetic field is using materials structured at the sub wave-length scale: metamaterials. With exotic properties not found in nature, metamaterials have revolutionised our ability to control fields, including light, sound, vibration, and heat. However, despite intensive research interest for almost two decades, the problem of designing metamaterials for specific applications remains challenging. Typical methods either make limiting assumptions, such as only allowing phase to be controlled, or rely on a large number of full-wave simulations. These are particularly expensive for metamaterials as there is a large length scale separation between the sub-wavelength elements of the metamaterial and the tens to hundreds of wavelength size of the metamaterial. Additionally, there has been much interest in using genetic algorithms or machine learning techniques to design materials, although these can be hard to interpret
In this thesis, we attempt to address some of these issues. Employing the coupled dipole approximation to model metamaterials as collections of dipolar scatterers, we derive a perturbative method for designing metamaterials for a wide range of applications. After formulating the basic method, we proceed to extend it to design multi-functional metamaterials, allowing functionality to be multiplexed. Simple proof-of-concept experiments outline some of the key challenges to realising the structures we design, indicating where future development efforts could be focused. Switching focus to the elements that make up the metamaterials, we then consider how the resonances of individual meta-atoms can be manipulated. In this context, we derive both analytic and numerical approaches to control the scattering for dielectric slabs, cylinders and spheres. | en_GB |
