Plasmonic Cover, May Render Object Invisible
Andrea Alù and Nader Engheta of the University of Pennsylvania in Philadelphia have conceived a technology that may exceed the capabilities of the current sophisticated camouflage systems used today. Their concept involves using Plasmon waves, which will reduce the scattering of light when it strikes an object. That scattering of light is what makes object visible to the eye.
The key to the concept is to reduce light scattering. We see objects because light bounces off them; if this scattering of light could be prevented (and if the objects didn’t absorb any light) they would become invisible. Alù and Engheta’s plasmonic screen suppresses scattering by resonating in tune with the illuminating light.
Plasmons are waves of electron density, caused when the electrons on the surface of a metallic material move in rhythm. The researchers say that a shell of plasmonic material will scatter light negligibly if the light’s frequency is close to the resonant frequency of the plasmons. The scattering from the shell effectively cancels out the scattering from the object.
For visible-light shielding, says Engheta, nature has already provided suitable plasmonic materials: silver and gold. To reduce the scattering of longer-wavelength radiation such as microwaves, one could make the shield from a ‘metamaterial’: a large-scale structure with unusual electromagnetic properties, typically constructed from arrays of wire loops and coils.
Alù and Engheta’s calculations show that spherical or cylindrical objects coated with such plasmonic shields do indeed produce very little light scattering. It is as though, when lit by light of the right wavelength, the objects become extremely small, so small that they cannot be seen.
The idea is still in the theoretical stage but it appears to be sound from a physics standpoint. Also according to theory, the technology will work better on small objects, optimally, it will work best when the wavelength of the light is the same size as the object being shielded, which basically means ‘microscopic’ items. At this point the object can’t be shielded from daylight because it is made up of various light wavelengths, and the Plasmonic cover will work when it is tuned to one specific light frequency. The theory is new and is sure to change when it is understood better. So don’t rule out the possibility of having a cloaking device just yet.