Thursday, May 12, 2005

Plasmonic Cover - Invisibility Sheild Mark I

` Is it possible to bend light waves in such a way as to make an object appear so tiny it's invisible?
` According to an old Nature article (which I said I'd bring up!) that's what they're working on!

` What is light? Aside from being made of particles called photons, it is also a wave that can resonate in all manner of frequencies - but that's quantum physics for ya.

` The idea is; if light didn't interact with objects by being scattered or absorbed, we wouldn't see them! If a true invisibility shield was built, it would have to reduce this interaction, if not eliminate it. Now, Drs. Alu and Engheta's plasmonic screen suppresses scattering by resonating in tune with the illuminating light.

` Why's it called a plasmonic screen? Well, plasmons are waves of electron density, caused when the electrons on the surface of a metallic material move in rhythm. A shell of this material will only just barely scatter light if the light's frequency is close to the resonant frequency of the plasmons. In other words, when you have plasmons vibrating at the same frequency as the light shining on it, then the scattering of the shell cancels out the scattering from the object.

` Silver and gold are pretty good for visible light sheilding (i.e. all colors we can see). For scattering longer-wavelength light, such as microwaves, what you need then is a large-scale structure with unusual electromagnetic properties, typically constructed from arrays of wire loops and coils.
` Spherical or cylindrical objects coated with plasmonic shells actually do produce little light scattering. It is as though, when lit by light of only one certain wavelength, the objects become too small to see!

` Really, the shield would have to be delicately tuned to suit the different objects it hides. Also, a particular shield only works for one specific wavelength. An object might be made invisible in red light, but not daylight. The effect only works when the wavelength of the light being scattered is about the same size as the object. This means that shielding from invisible light, would be possible for only microscopic objects. Other, larger ones could be hidden to long-wave raditation like microwaves. In other words, you can't hide things even as big as people from human vision.

` So what exciting inventions are they going to use it for? Antiglare materials! Of course! You see, microscopes could be higher-resolution by using tiny probes to measure the light field next to the object while at the same time being invisible!
` However, a spaceship could be made invisible to long-wavelength sensors and telescopes, so at least it has at least one really cool application.

` Anyway, I have actual recent science stuff to read soon, and if I don't, it'll disappear forever unless I pay lots of money. Tra-la!

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