The Invisibility Cloak

One of the many fantasies of humans is to become invisible. We’ve seen it being portrayed in movies, books, sci-fi series on TV and even some technical papers.
While I was surfing recently, I found out about Nader Engheta and Andrea Alu of the University of Pennsylvania who have submitted a scientific paper on how to make an object invisible.

More info about this story can be viewed at Live Science.
The technical paper can be downloaded in pdf format from Arxiv.

The proposal involves using plasmons — tiny electronic excitations on the surfaces of some metals — to cancel out the visible light or other radiation coming from an object. In short, plasmonic coatings can be used to make an object invisible.

But I thought of an easier way to achieve the same. We can make an object invisible by just using some electronics. Let us see how.

We know that what we see is nothing but wavelengths of light falling in the visible spectrum. UV and IR cannot be comprehended by our human eyes. So, UV and IR rays are invisible to us. So, can we make a body invisible by making it absorb or reflect all wavelengths? No, in that case it will become either a black body or a white one. So, for making it completely invisible we need to make its refractive index nearer to 1. Refractive Index of glass is about 1.5. Thus, it is transparent. A clean glass cannot be ‘seen’ by our eyes. This same principle is used for this freaky theory (or rather invention).

Let us examine this setup. We have a rectangular parallelepiped (or prism) as shown in figure inv01.jpg. Light rays strike the plane PQRS. These light rays constitute a combination of different wavelengths of light with different direction as well as intensities. Let plane PQRS be filled with minute photoreceptors which can calculate the above details. Thus we’ll get a photographic image in electronic format. This info can be stored in a microprocessor placed inside the prism. Now the plane ABCD consists of light emitters, which can emit light of all wavelengths, intensities and directions. These emitters too are connected to the microprocessor. The receptors as well as emitters are connected to the microprocessor using fiber optic cables. This will ensure that the extra distance covered by light will be as less as possible.

The working can be better explained in the second figure inv02.jpg. Light rays from the object are absorbed by the screen at PQRS and emitted from ABCD. Thus in the figure, observers 1 and 2 will see the object placed behind the prism. The people and objects placed in between PQRS and ABCD will thus become invisible! Our target is thus achieved.

Now let’s see the other criteria that should be taken into account to make sure that detection of this prism and its contents will not be possible.

1> Observers should not collide with the prism!
2> The light emitted by the emitters may produce a different interference pattern.
3> No matter how efficient, there will always be a time lag (i.e. RI can never be 1). This can be detected by using some machine. But for a normal human, the screen will still be invisible.
4> Man has stereoscopic vision. So, one may detect a small difference between the real image and the emitted image.
5> The prism should have a clean surface. Dust may get collected.
6> Rain drops and snow may accumulate on this screen and seriously damage its functionality. Thus the screen should be made unaffected from atmospheric elements.
7> Efficiency can never be 100%
8> If there is relative velocity between the screen and observer, he may be able to guess that something is amiss.
9> Light hitting the emitters should not get reflected. It should be absorbed by the emitters.
10> The screen will be seen on a thermo or Infrared cameras. Of course, this can be neutralized.

This method will have a variety of application starting from the entertainment industry to technological advancements in defense.

This is my original idea. If I get the opportunity, I’ll surely develop this idea and construct one invisibility screen (or cloak). If someone wants to develop or use it, please mail me or comment on this post.

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