July 9, 2009 feature
Transform a ball into a rock -- or make it invisible -- using transformation optics
(麻豆淫院Org.com) -- Science fiction and fantasy tales are full of the ability to "cloak" characters with invisibility. Whether it is a spaceship with a cloaking device, or a young wizard with an invisibility cloak, the interest in rendering someone or something invisible captures our fancy. Scientists have succeeded in creating the illusion of invisibility by bending light around a region for concealment. These types of devices have limitations, however; one of these limitation that the device normally has to be touching the object to be rendered invisible - or in very close proximity.
Instead of bending light, though, what if transformation optics was used to create invisibility - or even give an object the appearance of a completely different object? A team of theorists at the Hong Kong University of Science and Technology propose a technique that might be able to accomplish just that, with a remote device. The group鈥檚 proposal appears in 麻豆淫院ical Review Letters: 鈥�Illusion Optics: The Optical Transformation of an Object into Another Object.鈥�
鈥淩ight now, invisibility devices bend light, steering it around an object to make it appear transparent, as if it weren鈥檛 there,鈥� Che Ting Chan tells 麻豆淫院Org.com. Chan is one of the scientists who proposed the idea of a device that would use illusion optics to transform objects within a confined space. 鈥淥ur proposed device would have special properties. It would employ a type of illusion that makes an object look exactly like another object.鈥�
Metamaterials, which are manmade with special properties, would be used. A 鈥渃omplementary medium鈥� would be employed to optically cancel a specified area. Then, a 鈥渞estoring medium鈥� would be used to make the cancelled space 鈥渞eappear鈥� as something else. For invisibility, the restored area would look like air. 鈥淚f it looks like air,鈥� Chan explains, 鈥渢hen it is transparent. You can see through it. It is like making something invisible.鈥� This method could also, theoretically, be used to 鈥渢ransform鈥� objects. 鈥淵ou could make a ball look like a rock,鈥� Chan says. 鈥淵ou could hide something in plain sight, as something else.鈥�
In addition to transforming the way an object looks to others, this device would have another advantage over current invisibility devices. 鈥淵ou wouldn鈥檛 have to need the device to touch the object being hidden,鈥� Chan insists. 鈥淵ou could remotely control a particular area to entirely exclude a specific wave without having to be as close.鈥�
While the device sounds promising, Chan admits that there are difficulties involved in building such a cloak. 鈥淚n addition to positive refractive material, which is not a big problem, we would require a negative refractive index.鈥� Positive refractive materials are easily made, but something with a negative refractive index would require special design. 鈥淪ome sort of structure to create a phase delay would be needed,鈥� Chan says.
Chan and the Hong Kong team are working on interesting experimentalists in the concept. 鈥淲e are dealing with electromagnetic waves,鈥� Chan explains, 鈥渂ut there are those who are doing similar experiments with acoustic waves. Maybe if our idea was applied to acoustic waves first, it would be easier to see how to extend it to include light.鈥�
More Information: Yun Lai, Jack Ng, HuanYang Chen, DeZhuan Han, JunJun Xiao, Zhao-Qing Zhang, and C.T. Chan, 鈥淚llusion Optics: The Optical Transformation of an Object into Another Object,鈥� 麻豆淫院ical Review Letters (2009). Available online: .
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