We expect the world to be predictable. Water flows downhill, fire burns and lenses bend light in a particular way. That worldview took a jolt as Isaac Ehrenberg, an MIT graduate student in mechanical engineering, developed a three-dimensional, lightweight metamaterial lens that focuses radio waves with extreme precision. That may not seem too disturbing, but the lens is concave and works in exactly the opposite manner of how such a lens should.
Metamaterials have an air of magic about them. The elements they’re made out of should work one way, but they way they’ve been fabricated make them operate in another. They are ordinary substances that have been engineered with precisely designed and fabricated microscopic structures. These structures interact with light or sound in such a way that they produce effects that are not found in nature. In the case of the MIT metamaterial lens, they result in a concave lens that should spread radio waves, but focuses them instead.
The lens is produced by blocky, S-shaped “unit cells” a few millimeters wide that refract radio waves in particular directions. The roughly concave lens is formed from 4,000 of these cells. They were fabricated from a polymer by means of 3D printing into a self-supporting structure, and then coated with a fine mist of copper. The 3D fabrication technique meant that there was little energy lost as the radio energy passed through the lens, which was a problem with previous lenses made of stacked 2D structures.
The lens produces a level of focus that is so precise that it has the potential for imaging individual molecules. It also has the advantage of being lightweight, which Ehrenberg claims would make it practical for sending into orbit for astronomical observations.
The results of the MIT team were published by Ehrenberg and his colleagues Sanjay Sarma, and Bae-Ian Wu in the Journal of Applied Physics.