Original URL: http://www.theregister.co.uk/2006/05/04/cloaking_device/
Scientists moot Romulan-style cloaking device
Cunning 'anomalous localised resonance' plan
Two mathematicians have boldly gone where no boffin has gone before and described the theoretical possibility of a cloaking device, the BBC reports.
However, before the Trekkies among you don your Romulan cozzies and rush for a copy of the Royal Society publication in which Nicolae Nicorovici and Graeme Milton expound their cloak of invisibility, be aware it's very much a paper concept, currently applicable only to small objects of a particular range of shapes.
The theory is based on "anomalous localised resonance" - analogous to the effect by which a vibrating tuning fork placed close to a wine glass will cause the latter to vibrate, as the Beeb notes. Nicorovici and Milton say an illuminated speck of dust (yup, that's the scale we're talking about), in close proximity to a "superlens*" cloaking material, would "scatter light at frequencies that induce a strong, finely tuned resonance in a cloaking material placed very close by". Said resonance cancels out the light coming from the speck, and voila! - invisibility.
At least, that's the plan. Superlens pioneer Sir John Pendry, of Imperial College London, said of the mathematicians' admission that "the cloaking effect works only at certain frequencies of light, so that some objects placed near the cloak might only partially disappear": "I believe their claims about the speck of dust and a certain class of objects. In the paper, they do give an instance about a particular shape of material they can't cloak. So they can't cloak everything."
He further explained: "Providing the specks of dust are within the cloaked area, the effect will happen. A cloak that only fits one particular set of circumstances is very restrictive - you can't redesign the furniture without redesigning the cloak."
Accordingly, we don't think Starfleet Command will be losing any sleep over this one just yet.
Nicorovici and Milton's research is published in the Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences. ®
*The superlens's basic purpose is to break the "diffraction limit" which "restricts the resolution of microscopes and other optical devices to the wavelength of light used", as physicsweb puts it in its illuminating and comprehensive technical description. Here's more:
Diffraction restricts the resolution of microscopes and other optical devices to the wavelength of light used. To see why, imagine two widely spaced apertures that are illuminated by the same beam of light so that each aperture produces its own diffraction pattern. If the apertures are moved closer together, their diffraction patterns overlap until they eventually merge to form a single peak. The individual apertures can then no longer be resolved by observing the transmitted light. This unwanted effect is known as the diffraction limit.
As is often the case in physics, this simple picture is a little more complicated in practice because light that squeezes through a sub-wavelength aperture emerges in two portions. First there is a "far-field" portion that propagates away from the aperture and can be refocused by conventional lenses. Then there is a "near-field" portion that stays put, remaining localsed around the aperture over a region less than a wavelength in size.
The near-field portion contains all of the sub-wavelength spatial details about an object, but it decays quickly as a function of distance from the object. Conventional optical devices are therefore unable to convey these finer details to an image. Instead, such instruments are constrained to recover as much of the far-field light as possible, limiting their resolution to roughly the wavelength of light.
The idea, then, is to produce a lens capable of recovering the near-field and far-field components, in which case "an exact image of the object could be formed with perfect resolution".
That's exactly what two teams did with a thin layer of silver which, working with visible light, "can be used to image structures with a resolution as high as one-quarter the wavelength of the incident light".