Metamaterials: Hiding Tanks, Not Boy Wizards

invisibility on a very small scale
Image courtesy the University of Maryland Department of Electrical and Computer Engineering
This optical image shows the University of Maryland metamaterials in action, steering light waves away from the central circle. The arrows indicate the direction of the light waves.

Take a good look at an object on your desk -- say the unwashed coffee cup or that canister of Red Bull you're nursing. Seriously, why all the caffeine? As you stare at this object, ponder this: You've never actually seen this object before and you're not really seeing it now. You're actually seeing light -- that's all our eyes can sense.

Your eyes are processing the light leaving that shiny silver canister, light originating from a lamp or the world outside a nearby window. If we could somehow keep the light from intercepting the object in question, you wouldn't be able to see it.

In 2007, the University of Maryland's Igor Smolyaninov led his team even farther down the road to invisibility. Incorporating earlier theories proposed by Purdue University's Vladimir Shaleav, Smolyaninov constructed a metamaterial capable of bending visible light around an object.

A mere 10 micrometers wide, the Purdue cloak uses concentric gold rings injected with polarized cyan light. These rings steer incoming light waves away from the hidden object, effectively making it invisible. Chinese physicists at Wuhan University have taken this concept into the audible range, proposing the creation of an acoustic invisibility cloak capable of diverting sound waves around an object.

For the time being, metamaterial invisibility cloaks are somewhat limited. They're not only small; they're limited to two dimensions -- hardly what you'd need to vanish into the scenery of a 3-D war zone. Plus, the resulting cloak would weigh more than even a full-grown wizard could hope to lug around. As a result, the technology might be better suited to applications such as hiding stationary buildings or vehicles, such as a tank.

Explore the links on the next page to learn more about invisible tanks and other cutting-edge technologies.