Engineers have found ways to endow ordinary materials with intricate microstructures, creating “metamaterials” that can curve light around very small objects and make them invisible. But metamaterials have bent light too weakly to conceal larger objects. Even an item as small as a penny was impossible to cloak—until two big advances last year.
In January independent teams at MIT and the University of Birmingham showed how to use calcite (a common crystal) to make paperclip-size objects disappear. Later in the year, optical physicist Bumki Min of the Korea Advanced Institute of Science and Technology got a different light-bending idea after reading about a Duke University cloaking device composed of 2-millimeter-wide plastic cells. As the gap between copper components within the cells narrowed, their light-bending power increased. By reducing the gap to less than 3 microns—the width of a strand of spider silk—Min could bend light to nearly a right angle, allowing it to wrap more snugly around objects.