Professor Snape beware — invisibility cloaks aren’t just for the microscopic anymore.
Using natural crystals, two independent research teams have designed “carpet cloaks” that can abracadabra 3-D objects as big as an ant or a grain of sand seemingly into nothing. Up to now, making things invisible has relied on tiny structures called metamaterials. These fabrications are often a mix of stacks and crisscrosses of nano-sized metals and other materials that can guide electromagnetic rays, such as microwaves or infrared and visible light, around objects. If researchers tweak metamaterials just right, they can make tiny things disappear — at certain light wavelengths and from certain angles, at least.
But now two teams, including an MIT group that published its results online in Physical Review Letters January 18 and another from England and Denmark that published online February 1 in Nature Communications, didn’t bother with metamaterials. They adopted calcite prisms, a type of naturally occurring crystal, to build carpet cloaks. Carpet cloaks aren’t true now-you-see-them-now-you-don’t apparatuses. The bottom of the cloaking device is notched with a small triangle that looks like a bent mirror. Thanks to the optical properties of metamaterials or, in this case, calcite, the bent mirror can look like a flat plane when viewed from some angles. Anything hiding in the notch vanishes.