Any Harry Potter fan knows that it would have been difficult for Harry to sneak around Hogwarts without the use of his silvery invisibility cloak. Also, Star Trek fans will remember the cloaking devices that appeared on that show. Of course this is only possible in the realm of fantasy, is it not? Perhaps not, as scientists have now invented “metamaterials” that may make a real-life invisibility cloak possible
Normally, materials behave as we think materials should in regards to reflecting light. For example, we can see a chair because electromagnetic waves of light interact with the material that makes up the chair. In 2000, however, John Pendry, a physicist at Imperial College London, proposed a superlens with a negative refractive index, meaning that whenever light hit it, it would reverse and go in the opposite direction, thus canceling out light.
Scientists have now taken the next step with the development of “metamaterials,” artificial materials in which the sum of the parts, not the parts themselves, determine how they will interact with light. These materials have a negative refractive index. This means that the incoming light waves are refracted “through” the materials rather than back to the source of the light, thus allowing them to act as “invisibility” cloaks. In essence, the metamaterials could make an object invisible by bending light waves so that they curve around the object and then reconnect. A group from the University of California, Berkeley, were the first to demonstrate the use of these materials.
One of the new metamaterials, described in Science, is composed of silver wires, each about 20 times thinner than a human hair, embedded in aluminum oxide. Another metamaterial, described in Nature, is a layer cake of alternating nanoscale strips of silver and magnesium fluoride that are cut into a fishnet pattern. Both materials cause visible light to bend in a different direction than expected. The light is bent around to the other side as though nothing was there. If the light can be guided around the object and back to its original course, there will not even be a shadow.
Now researchers from Imperial College London have developed the first non-resonate metamaterial that operates with light waves of zero frequency. This is different than the studies that focused on microwaves and visible light. With zero frequency, the wave length is very large and magnetism and electricity are separated, allowing physicists to work with the magnetic properties without worrying about the electrical properties when designing something like a cloak. This new metamaterial is made of layers of stacked lattices composed of thin lead plates.
There are many other possible uses for this technology. For example, an antenna could be cloaked if it was interfering with another antenna close by. An obstruction to cell phones could also be cloaked. Also, if you can hide something from microwaves, you can hide it from radar a fact that will no doubt interest law enforcement and the military.
Harry Potter and Captain Kirk would be proud.
