'Cloak' makes objects invisible to microwaves - <em>News release</em>
Imperial College London News Release
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Thursday 19 October 2006.
Scientists have demonstrated the first ever working 'invisibility cloak', reports Science Express today. The team of researchers from Duke University, USA, worked with Professor Sir John Pendry of Imperial College London to create a prototype 'cloak' based on a new design theory proposed by the same team earlier this year.
The cloak deflects microwave beams as they flow around an object hidden inside it, in the same way that water in a river flows around a stick. The Duke scientists have proven that the object inside the cloak is rendered invisible to microwaves, which could, in the long run, have a variety of applications for radar and communications technologies.
The researchers at Duke University used theoretical designs published in an earlier Science paper  to build a small cloak, less than five inches across, which would provide invisibility in two dimensions. The cloak was built using specially-manufactured 'metamaterials' which 'grab' light heading towards the cloak and make it flow smoothly around the cloak instead of striking it.
To test the prototype cloak, the researchers aimed a microwave beam at it inside a test chamber between two metal plates, and then measured the electromagnetic fields both inside and outside the cloak. Their measurements showed that the electromagnetic waves separated and flowed around the centre of the cloak, as predicted by theory.
Sir John said: "Our first paper developed the concept of a cloak but there remained the huge challenge of making this a reality. We knew that no naturally occurring materials would do the job, but the new class of metamaterials which owe their properties to their internal structure rather than their chemistry, have proved yet again that they can meet some of the most extreme challenges."
Sir John and his collaborators at Duke are concentrating on perfecting their cloaking technology for microwaves, and are hoping to develop a three-dimensional cloak for invisibility to microwaves.
The metamaterials used to build the cloak are fashioned into concentric two-dimensional rings, which interact with magnetic waves in a very specific way. The precise variations in the shape of the copper element used determine the cloak’s electromagnetic properties. The cloak is thought to be one of the most complex metamaterial structures ever made, as it has a unique circular geometry and it’s electromagnetic properties vary across its surface.
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Notes to Editors:
1. "Metamaterial Electromagnetic Cloak at Microwave Frequencies", Science Express, 19 October 2006.
D. Schurig (1), J. J. Mock (1), B. J. Justice (1), S. A. Cummer (1), J. B. Pendry (2), A. F. Starr (3), D. R. Smith (1).
(1) Department of Electrical and Computer Engineering, Duke University, Box 90291, Durham, NC 27708, USA.
(2) Department of Physics, The Blackett Laboratory, Imperial College London, SW7 2AZ, UK.
(3) SensorMetrix, San Diego, CA, USA.
2. "Controlling Electromagnetic Fields" Science 312 1780-2 (2006). JB Pendry, D Schurig, and DR Smith.
3. Consistently rated in the top three UK university institutions, Imperial College London is a world leading science-based university whose reputation for excellence in teaching and research attracts students (11,000) and staff (6,000) of the highest international quality. Innovative research at the College explores the interface between science, medicine, engineering and management and delivers practical solutions that enhance the quality of life and the environment - underpinned by a dynamic enterprise culture. Website: www.imperial.ac.uk.
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