Cloaking device

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.

Overview

A recent review said these methods were possible:

1. 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.
2. 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.
3. 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.
4. 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.

Cloaking Device Media

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  A coat using optical camouflage by Susumu *Tachi.* Left: The coat seen without a special device. Right: The same coat seen though the half-mirror projector part of the Retro-Reflective Projection Technology.