Researchers at MIT have now fabricated a three-dimensional, lightweight metamaterial lens that focuses radio waves with extreme precision. The concave lens exhibits a property called negative refraction, bending electromagnetic waves — in this case, radio waves — in exactly the opposite sense from which a normal concave lens would work.Concave lenses typically radiate radio waves like spokes
For Isaac Ehrenberg, an MIT graduate student in mechanical engineering, the device evokes an image from the movie “Star Wars”: the Death Star, a space station that shoots laser beams from a concave dish, the lasers converging to a point to destroy nearby planets. While the researchers’ fabricated lens won’t be blasting any planetary bodies in the near future, Ehrenberg says there are other potential applications for the device, such as molecular and deep-space imaging.
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
To fabricate his design, Ehrenberg utilized 3-D printing, building a lens layer by intricate layer from a polymer solution. He 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.To test the lens, the researchers placed the device between two radio antennae and measured the energy transmitted through it. Ehrenberg found that most of the energy was able to travel through the lens, with very little lost within the metamaterial — a significant improvement in energy efficiency when compared with past negative-refraction designs.
The team also found that radio waves converged in front of the lens at a very specific point, creating a tight, focused beam.Imaging space and beyondSarma says the combination of the device’s “low loss” and tight focus is a promising step toward engineering practical metamaterial lenses.“There are a lot of phenomena in the world that you can demonstrate, but whether you can achieve it at scale is the issue,” Sarma says. “We’ve taken the negative refraction concept from the realm of proof-of-concept to the realm of practicality.”The device, which weighs less than a pound, may be used to focus radio waves precisely on molecules to create high-resolution images — images that are currently produced using bulky, heavy and expensive lenses. Ehrenberg says that such a lightweight device could also be mounted on satellites to image stars and other celestial bodies in space, “where you don’t want to bring up a hefty lens.”Cheng Sun, an assistant professor of mechanical engineering at Northwestern University, says the metamaterial design is a promising demonstration that may lead to stronger, faster telecommunications.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.