One approach to creating a cloaking device is using something called a superlens. A superlens has what's called a negative refraction index. This allows it to bend electromagnetic waves back upon themselves, in effect, using interference to render an object invisible.

Graeme Milton, of the University of Utah, is working on mathematical models for superlenses. Thus far, the technology is not shaping up to be something that would be feasible for hiding something large, like naval destroyers. "We've seen it numerically -- not in practice, but we've got a theoretical proof that collections of particles become invisible," said Milton of their superlens work.

While superlensing may not be the answer for making warships invisible, work with metamaterials looks like it may hold more promise for large objects. A group at Duke University, led by David Smith, has used copper-based metamaterials to create something of a cloaking cylinder.

Similar to the University of Maryland's plasmon-based cloaking device, the Duke team's metamaterial cylinder causes microwaves to be bent around itself rather than reflected. The cylinder has microscopic patterns on its surface and these patterns act to redirect the waves striking it, rather than allowing them to bounce off.

While the Duke cylinder is not perfect -- it still suffers from distortion which can be seen in microwave images -- it does have implications for some real applications. The devices could be used to prevent objects from causing electromagnetic interference. For example, hiding two antennas from each other, or cloaking an object that obstructs cell phone reception.

While the technology is not mature, Smith's group says it also has similar implications for bending sound waves around an object. Creative uses could act to prevent sound from escaping in a certain direction or hide an object from echolocation technology like sonar.