Invisibility Cloak By Harsha

Origins  In folklore, mythology and fairytales, a cloak of invisibility appears as a magical item used by characters. Also, it was used very frequently in the Harry Potter series.

Concept The device obscures a defined two dimensional region and only at a particular microwave frequency. Work on achieving similar results with visible light is in progress. Other types of invisibility cloak are also possible, including ones that cloak events rather than objects. However, cloaking a human-sized object at visible wavelengths appears to have low probability. Indeed, there appears to be a fundamental problem with these devices as "invisibility cloaks" It's not yet clear that you're going to get the invisibility that everyone thinks about with Star Trek cloaking device or the Harry Potter's cloak. To make an object literally vanish before a person's eyes, a cloak would have to simultaneously interact with all of the wavelengths, or colors, that make up light.

Illustration

Recent Experiments A new cloaking system was announced in the beginning of 2011 that is effective in visible light and hides macroscopic objects, i.e. objects that can be seen with the human eye. The cloak is constructed from ordinary, and easily obtainable calcite. The crystal consists of two pieces configured according to specific parameters. The calcite is able to refract the light around a solid object positioned between the crystals. The system employs the natural birefringence of the calcite. From outside the system the object is not visible "for at least 3 orders of magnitude larger than the wavelength of light in all three dimensions." The calcite solves for the limitations of attempting to cloak with metallic inclusions - this method does not require a nanofabrication process as has become necessary with the other methods of cloaking. The nanofabrication process is time consuming and limits the size of the cloaked region to a microscopic area. The system works best under green light. In addition the researchers appear to be optimistic about a practical cloaking device in the future.