We shall explore how one can attain control of the propagation of microwave surface waves via variation of the geometry of elements that make up a metamaterial surface. For example, one can induce a change in the phase of reflection from a surface to provide a virtual tilt to a reflector, or replicate the response of a parabolic dish. In addition, one can create ‘virtual’ waveguides on the surface of the array by either laterally grading the geometry deformation and hence the surface impedance. We envisage the development of surface wave devices such as beam splitters or combiners, and tapers and focussing or collimating systems for surface power, and will seek to employ either finite element (FEM) or finite difference time domain (FDTD) methods The project is funded through an EPSRC doctoral training grant, undertaken by Lizzy Brock, and supervised by Dr Alastair Hibbins.

Microwave characteristics of tessellated surfaces

This project investigates new topology and material combinations for use as microwave absorbers. This includes the study of tessellated surfaces as impedance matched layers, comprised of subwavelength-sized permittivity- and permeability- dominated patches .These novel designs will offer improvements in performance, and reduction in thickness over existing technologies. The studentship is funded by Dstl and the EPSRC for 3.5 years from September 2008, undertaken by Matthew Biginton, and supervised by Prof Roy Sambles and Dr Alastair Hibbins (University of Exeter) and Dr Ian Youngs (Dstl).

Extended Bandwidth Metamaterials

This project is concerned with understanding and developing novel multilayer structures with broadband transmission and absorption characteristics in the microwave regime. This includes tuning multiple resonant systems, manipulating surface waves using patterned metallic surfaces, and increasing electromagnetic bandwidths. The project is funded by QinetiQ and the EPSRC for 3.5 years from October 2008, undertaken by Celia Butler, and supervised by Dr Alastair Hibbins and Prof Roy Sambles (University of Exeter) and Dr Peter Hobson (QinetiQ).

An exploration of patterned thin layers of metal-dielectric composite materials for microwave absorption

The aim is to develop an analytical model to characterize the EM properties of 3D random composite materials for areas such as the aerospace, defence and medical industries. The relationship between the material parameters of the individual constituents, particle geometry, spatial arrangement and the concentration of particulates and how they determine the effective properties of the composite material is investigated. The project is funded by the University of Exeter and BAE Systems for 3 years from September 2008, undertaken by Melita Taylor, and supervised by Prof Roy Sambles and Dr Alastair Hibbins (University of Exeter) and Dr Sajad Haq (BAE Systems).

Microwave studies on thin structured films

The aim of this work is to look at the microwave transmission and reflection response of thin metal/dielectric composite films in order to look at useful and interesting electromagnetic phenomena. This includes behaviour such as selective transmission/absorption, enhanced transmission, frequency selection and negative refraction The project is funded by Dstl and EPSRC for 3.5 years from August 2007, undertaken by James Edmunds, and supervised by Prof Roy Sambles and Dr Alastair Hibbins (University of Exeter) and Dr Ian Youngs (Dstl).

Detailed study of zigzag metal gratings

There have been many recent and exciting advances in photonics demonstrating that metallic structures can be patterned on the subwavelength scale to exhibit novel electromagnetic properties not found naturally. While the term "metamaterial" has only recently been coined to describe these structures, perhaps the most famous example of a metamaterial is the simple diffraction grating. It was first studied in the late 18th century, finding use in spectroscopy in the early part of the nineteenth century, with mass production of reflection gratings following due to the development of ruling engines. Since then, this fundamental device has been employed extensively across the whole electromagnetic spectrum. In recent years considerable attention has been focused upon the study of metal transmission gratings structured on the subwavelength scale, this renewed interest largely being due to the observation of enhanced transmission phenomena associated with the excitation of waveguide and surface plasmon resonances.

Zigzag structures present an entirely new, and as yet completely overlooked type of metamaterial, the study of which will draw together a number of highly topical and active research areas. We are undertaking a programme of computer modelling, fabrication and experimental characterisation at both visible and millimeter wavelengths. The first subproject will use zigzag gratings to provide a mechanism for visible radiation to couple to the surface modes (surface plasmons) that exist on silver and gold films. However, at microwave frequencies, where metals are almost perfect conductors, no bound surface waves exist. Therefore we must rely on the perturbation of the surface itself to induce the necessary boundary conditions so that localised surface modes can be supported at all. Coupling to both traditional surface plasmons, and the microwave equivalent, will allow for an exploration of the modes' propagation and dispersion on surfaces with novel symmetries not previously considered, including those with chiral properties. We therefore expect to observe an interesting polarisation response, with the surface able to couple both transverse magnetic and transverse electric radiation into surface modes, and potentially strong polarisation conversion from blazed gratings. We have already produced a theoretical treatment for the interaction of electromagnetic radiation with such a structure, and a vital part of the project will therefore be to develop this theory into a computer code. This will not only allow for a comparison to the experimental data, but also an opportunity to discover the most interesting phenomena by quickly modelling the whole of parameter space associated with these exciting structures. We will also utilise commercial numerical modelling software, which while much slower, will enable the researchers to optimise and study the structures from the outset.

This EPSRC project (EP/G022550/1) is led by Prof Roy Sambles and Dr Alastair Hibbins, and supports two PhD students (Helen Rance and Tom Constant).

We wish to acknowledge the financial support of

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