By Cat Wood | December 04, 2012 2:56 pm

Nathan Landry, a graduate student in the Pratt School of Engineering, displays the cloaking device that he developed while working in professor David Smith’s lab
Photo credit: Duke University Photography

Most things in Harry Potter are made with magic, but it turns out that even us non-magic folk can create something seemingly magical: a type of invisibility cloak. Not with magic, but with science.

In 2006, researchers at Duke University created a prototype cloaking device, able to hide a small object from microwave radiation.

This simplified diagram shows how microwave beams flow around the cloak and emerge on the other side as if it was not there. Source: MSNBC

The cloak was made out of things called metamaterials, man-made structures that change the way electromagnetic waves act. Using these metamaterials, microwave beams can be bent around the cloak.

The effect is similar to how water flows around a rock in the middle of the stream. When something is placed in the middle of the cloak, the microwave beams are bent around that too. The end result: invisibility.

The prototype cloak was not perfect, however. Reflections of the microwave beams along the edges of the cloaking device prevented perfect invisibility. These reflections are similar to looking through clear glass in that while you can see through the glass, you still know it is there. In other words, there’s a slight reflection.

The scientists’ goal for the prototype, however, was to show that the basic concept worked, and it did.

Encouraged by this, two of the scientists on the original Duke team went back to work. This past year, Nathan Landy, a graduate student, and David R. Smith, a professor in the Engineering Department, revealed an updated version of the 2006 cloak. They were finally able to get rid of the reflections and create a device that completely hides an object from microwave radiation.

The key to the improvement lies in the shape. The new cloak is shaped like a diamond, which allows it to minimize reflections better than the previous cylindrical cloak did.

A snapshot of the microwave field for free space, with an object, and with the cloak. As you can see, there is almost no disturbance when the cloak is placed in the field, unlike when the object is used.
Source: Landy and Smith’s paper ‘The Perfect Invisibility Cloak’ in Nature Materials

There are still several things that need to be addressed before we can have invisibility cloaks like Harry Potter’s though.

For starters, the cloak’s size means it is only able to hide small objects. It is also a 2D cloak, meaning it works only when viewed from one side. It also doesn’t work with visible light. So while it is invisible to a microwave beam detector, the human eye will still able to observe it.

The reason why cloaks are created to work with microwave radiation and not visible light is due to the metamaterials used. Those needed to create a cloak for microwaves are much less complicated than those needed for visible light. In fact, the metamaterials that allow an object to be invisible to visible light have not yet been invented.

In other words, there is still a long way to go before we’ll be getting up to mischief using our invisibility cloaks. Landy and Smith’s new cloaking device is just one step closer to making that dream a reality. And guess what? They didn’t even have to use magic.

Related Articles:
Invisibility cloaking in ‘perfect’ demonstration
Will we ever really have invisibility cloaks?
The first ‘perfect’ invisibility cloak 

References: Landy, Nathan, and David R. Smith. “A full-parameter unidirectional metamaterial cloak for microwaves.”Nature Materials (2012). <http://www.nature.com/nmat/journal/vaop/ncurrent/full/nmat3476.html>

Categorized under: Materials Science, Metamaterials, Invisibility, Cloaking Devices
 
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