Manmade metamaterials are often seen as supernatural. They are ordinary substances but with their precisely designed structures they could produce effects, such as bending electromagnetic waves in ways that are impossible for materials found in nature.
Isaac Ehrenberg, an MIT graduate student in mechanical engineering, has now fabricated a three-dimensional, lightweight metamaterial lens that focuses radio waves with extreme precision. The concave lens exhibits a property called negative refraction: it bends radio waves in exactly the opposite manner from which a normal concave lens would work.
(The orientation of 4,000 S-shaped units forms a metamaterial lens that focuses radio waves with extreme precision, and very little energy lost. Photo: Dylan Erb)
Concave lenses typically radiate radio waves like spokes from a wheel. In this new metamaterial lens, however, radio waves converge, focusing on a single, precise point — a property impossible to replicate in natural materials.
A metamaterial can refract light differently depending on its structure - the shape and the arrangement of those units. Ehrenberg designed the unit shape based on a blocky, S-shaped "unit cell" previously developped by other team, and created the "rough shape from more than 4,000 unit cells, each only a few millimeters wide."
Using 3D printing Ehrenberg built a lens with polymer and then washed away any residue with a high-pressure water jet and coated each layer with a fine mist of copper to give the lens a conductive surface.
Compared to the previous negative-refraction designs the new lens made of 3D printing technology has a significant improvement in energy efficiency. Most of the energy was able to travel through the lens, with very little lost within the metamaterial.
(a) Solid model of the S-ring unit cell, the response of which is polarization dependent, and (b) a photograph of the assembled planoconcave lens which consists of 7 metamaterial layers in the propagating direction. Source: aip.org
The device, which weighs less than a pound, may be used to focus radio waves precisely on molecules to create high-resolution images. Furthermore this lightweight devices can be mounted on satellites to image stars and other celestial bodies in space, said Ehrenberg.
"The low-loss design can be considered a significant step forward toward practical applications at microwave or radio-frequencies ranges," says Cheng Sun, an assistant professor of mechanical engineering at Northwestern University.
This simple and easily replicated fabrication method can be used by other scientists to explore the space of metamaterials, says Ehrenberg. "There's a whole other dimension that now people will be able to look into."
Ehrenberg published the results of his research in the Journal of Applied Physics. His co-authors on the paper are Sanjay Sarma, the Fred Fort Flowers and Daniel Fort Flowers Professor of Mechanical Engineering at MIT, and Bae-Ian Wu, a researcher at the Air Force Research Laboratory.
Posted in 3D Printing Applications
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