Invisibility Cloak - Myth or Reality?

     From Perseus’s helmet to Harry Potter’s cloak, the idea of an object that can render a person invisible has been a staple of fiction and mythology for eons. But for about the past year, physicists and materials scientists have been publishing papers that reveal real progress in turning science fiction into fact. And given the extraordinary work of these scientists, your children or their children might one day be able to pull off that trick as well. Let us now witness how the invisibility cloak comes within our sight.

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Invisibility Cloak "Bends Light Around Itself"

A cloaking device that makes objects invisible is being developed by researchers, bringing the magic of Harry Potter into the world of science fact.  While Harry uses his cloak of invisibility to move about Hogwarts School unseen, electronic engineers at the University of Pennsylvania are working on a real invisibility shield called a "plasmonic cover."  The development, which works by preventing objects from reflecting and scattering light, could have widespread use in the military as it would be more effective than current stealth technology.  Although no final product has been made, the engineers claim their proposal "does not obviously violate any of the laws of physics."

Other types of invisibility cloaks have been developed before, but these mostly use the "chameleon principle" - colouring objects to match their background, enabling them to blend in and become camouflaged.  One such system involved using light detectors and emitters that project a replica of the image appearing behind an object on to its front surface.  Similarly, researchers in Tokyo are developing a camouflage fabric that uses a comparable principle where the background is projected on to light-reflecting beads in the material.  Such systems are, however, dependent on the viewer from which the object is being concealed being in the right position.

A report in the journal Nature reveals that the new system is far more ambitious, being both self-contained and reducing visibility from all angles.  In this sense it would be more like the shields used by the Romulans in the Star Trek episode "Balance of Terror" which hid their spaceship at the touch of a button.  Dr John Pendry, a physicist at Imperial College London, said: "The concept is an interesting one.  It could find uses in stealth technology and camouflage."

According to Dr Andrea Alu and Dr Nader Engheta, the engineers behind the project, the key is to reduce light scattering.  Objects are visible because light bounces off them; if this can be prevented and if the objects did not reflect any light, they would become invisible.  The "plasmonic screen" achieves this by resonating in tune with the illuminating light.  Plasmons are created when the electrons on the surface of a metallic material move in rhythm.  The developers claim a shell of this material will reduce light-scatter to the extent that an object will become invisible, if the light’s frequency is close to the resonant frequency of these plasmons.  In this way, the scattering from the shell effectively cancels out the scattering from the object.

Article Source: Flatrock.org.nz