Posted on behalf of Zeeya Merali

Invisibility cloaks make the headlines on a pretty regular basis (usually accompanied by a reference to Harry Potter). But the working cloaks built so far haven’t quite lived up to the image that their name conjures because they cannot hide objects large enough to be seen with the naked eye, in visible light. Now, however, a UK group has published details in Nature Communications of a cloaking device made from calcite crystals that does just that -rendering objects up to a few centimetres tall invisible.

I wrote about this research, led by Shuang Zhang at the University of Birmingham and John Pendry at Imperial College London, UK, last December, when they posted a preprint describing the calcite cloak on the physics preprint database arXiv. (See Invisibility Rug Hides ‘Large’ Objects.)

That article describes the nuts and bolts of how the cloak, when placed over an object on the ground, bends light to give the illusion that there is nothing lying under it (An independent group based in Singapore also produced a similar cloak that works under water).

One of the most striking features of the new cloak is that it’s made from a cheap, readily-available natural substance and doesn’t take too much time or effort to build. By contrast, previous invisibility cloaks have been intricately-engineered from silicon microstructures, in an expensive and time-consuming process. Those “metamaterial cloaks” follow blueprints first laid out in 2006 by Pendry and colleagues, and independently by Ulf Leonhardt at St. Andrew’s University, UK.

Leonhardt, who has not worked on the new calcite cloak, praised it for its “beautiful” and “simple” design. “Cloaking has been inspired by research on metamaterials, but, ironically, these cloaking devices are almost home-made,” Leonhardt told me last December. “Even more ironically, John Pendry––the pope of metamaterials––is one of the authors.”

The calcite device should be relatively easy to scale-up — for bigger objects, you just need a bigger lump of calcite. However, it still cannot do everything you might ask of an invisibility cloak; it can only shield an object from light rays coming in from certain directions, so you won’t be able to use this design to build a wraparound cloak that you can wear and move around in. But even given this limitation, it’s impressive to think of the speed with which the invisibility cloak has bounded from blueprint to reality. And it’s a nice twist that, for once, building the thing is turning out to be far more straightforward than originally imagined.

Image: photo by Ariaski via Flickr under Creative Commons.