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Speaker: Professor Sir John Pendry, Imperial College London
Cloaks are already being designed and built that hide objects within them, but remain completely invisible to external observers. A new class of materials has created some extraordinary possibilities such as a negative refractive index, and lenses whose resolution is limited only by the precision with which we can manufacture them. The new materials, named metamaterials, have properties determined as much by their internal physical structure as by their chemical composition and the radical new properties to which they give access promise to transform our ability to control much of the electromagnetic spectrum. Electromagnetism encompasses much of modern technology. Its influence rests on our ability to deploy materials that can control the component electric and magnetic fields.
Professor Sir John Pendry is a condensed matter theorist. He has worked at the Blackett Laboratory, Imperial College London, since 1981. He began his career in the Cavendish Laboratory, Cambridge, followed by six years at the Daresbury Laboratory where he headed the theoretical group. He has worked extensively on electronic and structural properties of surfaces developing the theory of low energy diffraction and of electronic surface states. Another interest is transport in disordered systems where he produced a complete theory of the statistics of transport in one dimensional systems.
In 1992 he turned his attention to photonic materials and developed some of the first computer codes capable of handling these novel materials. This interest led to his present research, the subject of his lecture, which concerns the remarkable electromagnetic properties of materials where the normal response to electromagnetic fields is reversed leading to negative values for the refractive index. This innocent description hides a wealth of fascinating complications. In collaboration with scientists at The Marconi Company he designed a series of 'metamaterials' whose properties owed more to their micro-structure than to the constituent materials. These made accessible completely novel materials with properties not found in nature. Successively metamaterials with negative electrical permittivity, then with negative magnetic permeability were designed and constructed. These designs were subsequently the basis for the first material with a negative refractive index, a property predicted 40 years ago by a Russian scientist, but unrealised because of the absence of suitable materials. He went on to explore the surface excitations of the new negative materials and showed that these were part of the surface plasmon excitations familiar in metals. This project culminated in the proposal for a 'perfect lens' whose resolution is unlimited by wavelength. These concepts have stimulated further theoretical investigations and experiments by the Zhang group have confirmed the predicted properties. More recently, in collaboration with a team of scientists at Duke University, he has proposed a recipe for a cloak that can hide an arbitrary object from electromagnetic fields. A version of this design working at radar frequencies and exploiting the properties of metamaterials has now been implemented experimentally by the Duke team.
The simplicity of the new concepts together with their radical consequences have caught the imagination of the world's media generating much positive publicity for science in general.
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When & where
6.30pm - 8.30pmWednesday 29th October 2014