Invisibility Ring
25 October 2006

Scientists cannot yet make an invisibility cloak like the one that Harry Potter uses. However, for the first time, they have constructed a simple cloaking device that makes itself and something placed inside it invisible to microwaves.



This new, ring-shaped invisibility device is 1 centimeter tall and about the size of a drink coaster.
David Schurig et al./Science


When a person "sees" an object, his or her eye senses many different waves of visible light as they bounce off the object. The eye and brain then work together to organize these sensations and reconstruct the object's original shape.
In order to make an object invisible, scientists have to keep waves from bouncing off . They have to ensure that the object casts no shadow. Otherwise, the absence of reflected light on one side would give the object away.
Invisibility is not possible yet with waves of light that the human eye can see. However, it is now possible with microwaves.
Like visible light, microwaves are a form of radiant energy. They are part of the electromagnetic spectrum, which also includes radio waves, infrared light, ultraviolet rays, X- rays, and gamma rays. The wavelengths of microwaves are shorter than those of radio waves but longer than those of visible light.



Microwaves bent by the walls of this 1-centimeter-tall invisibility device skip the center area and come out the other side on their original paths as if nothing had been in the way.
David Schurig et al./Science

The scientists' new "invisibility device" is the size of a coaster and shaped like a ring. The ring is made of a special material with unusual abilities. When microwaves strike the ring, very few bounce off it. Instead, they pass through the ring, which bends the waves all the way around until they reach the opposite side. The waves then return to their original paths.
To a detector set up to receive microwaves on the other side of the ring, it looks as if the waves never changed their paths—as if there were no objects in the way! So, the ring is effectively invisible.
When the researchers put a small copper loop inside the ring, it, too, is nearly invisible.
However, the cloaking device and anything inside it do cast a pale shadow. This device works only for microwaves, not for visible light or any other kind of electromagnetic radiation.


Mohamed Gaber

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