Antennas may one day come in the form of flat materials that can be bent to custom shapes, in order to focus electromagnetic waves. 

Tie Jun Cui from Southeast University in Nanjing, China led the research leading to the new technology. 

The material was created by depositing tiny U-shaped structures onto a dielectric material. This allowed the surface to act like a Luneberg Lens, which has an unusual effect on light passing over its surface. 

Electromagnetic waves passing through materials can be bent or refracted, by the material. The degree to which the radiation is bent is referred to as the index of refraction. Most materials have a single index of refraction, providing a simple path for light to take while passing through the substance. 

Luneberg lenses have several different indexes of refraction, depending on where the light hits the material. Objects with this property are known as gradient-index lenses. This allows light to focus at unusual angles not possible with traditional designs. These unusual lenses can be created to refract a wide range of electromagnetic wavelengths, from visible light to radio waves. Traditional Luneberg lenses are curved, which is not ideal for all applications. 

"A conventional Luneburg lens can focus plane waves to a point at the edge of the lens, or radiate waves of the point source with high directivities. However, the curved focusing plane of the Luneburg lens is inconvenience in some applications. The quasi-conformal mapping provides a way to flatten the focusing plane," researchers wrote in the journal article.

Luneberg lenses are in use in a variety of applications, including microwave ovens and radar installations. Unlike traditional lenses, they can focus waves striking them from any angle. They are in a class of materials called metasurfaces or metamaterials, meaning they exhibit qualities not seen in any known natural substance. These materials are needed to create invisibility cloaks and perfect lenses, free from any distortion. 

Luneberg lenses were traditionally designed using geometric optics, which treats light in terms of rays. A newer method uses holographic optics. 

"We now have three systematical designing methods to manipulate the surface waves with inhomogeneous metasurfaces, the geometric optics, holographic optics, and transformation optics. These technologies can be combined to exploit more complicated applications," Cui said.

This development could lead to new antennas which are flat or could be bent into custom shapes to conform to nearly any shape desired. Using the new technology, a single antenna could track several incoming signals. This would allow listening on several satellites at once, greatly improving the efficiency of space communication systems.  

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