theoretical device to render objects invisible
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A cloaking device or invisibility cloak has long been featured in science fiction. Attempts have been made to devise a way to do it with objects, but results were disappointing until now. A paper in Nature Communications for September 2013 announces a new approach.
- "Invisibility cloaking was almost inconceivable until the ingenious theory of macroscopic invisibility cloaking was proposed based on transformation optics principles. ... We successfully demonstrate the cloaking of living creatures, a cat and a fish, from the eye.
From reference 1, the two "supplementary movies" show the successful cloaking of a goldfish and a cat so far as they are within the experimental space.
A recent review said these methods were possible: 
- Optical camouflage: A modified background image is projected onto a cloak of reflective material (the kind used to make projector screens). The wearer becomes invisible to anyone standing at the projection source.
- The "mirage effect": Electric current is passed through submerged carbon nanotubes to create very high local temperatures. This causes light to bounce off them, hiding objects behind.
- Adaptive heat cloaking: A camera records background temperatures, these are displayed by sheets of hexagonal pixels which change temperature very quickly, camouflaging even moving vehicles from heat-sensitive cameras.
- Calcite crystal prism: Calcite crystals send the two polarizations of light in different directions. By fixing prism-shaped crystals together in a particular way, polarised light can be directed around small objects. This effectively cloaks them.
- ↑ 1.0 1.1 Hongsheng Chen 2013. Ray-optics cloaking devices for large objects in incoherent natural light. Nature Communications. 4, 2652. 
- ↑ Leonhardt U. 2006. Optical conformal mapping. Science 312, 1777–1780.
- ↑ Pendry J.B; Schurig D. & Smith D.R. 2006. Controlling electromagnetic fields. Science 312, 1780–1782.
- ↑ Summary is from Morgan, James 2013. New 'invisibility cloak' type designed. BBC Science & Technology. 
- ↑ Monticone, Francesco & Alù Andrea 2013. Do cloaked objects really scatter less? Physical Review X, 3, #4.