Science has dealt another blow to those who draw their scientific knowledge from Star Wars films. Contrary to the famous line in the Empire Strikes Back,a new engineering approach called metamaterials can potentially cloak any size ship as long as you know what energy wavelength the other guy plans to use. So much for verisimilitude, George Lucas.
In brief, metamaterials assemble a repeated array of precisely-shaped materials to produce electromagnetic properties completely distinct from the raw material. For example a metamaterial lens tuned to the wavelength of visible light can apparently defy laws of physics by presenting a negative refractive index. That makes metamaterials useful for either making a microscope objective with infinite resolution or ‘warping’ light around a physical object, making it completely invisible from any angle. In effect, a cloaking device.
While wavelengths in visible light’s nanometer range remain out of reach for metamaterials engineers, the millimeter-scale wavelengths used in microwave applications like radar are much more accessible. The first metamaterials operated in that wavelength band, and now David Schurig and David Smith at Duke University have used it to build a functional radar cloak.
The cloak embodies the theory laid out by theorist John Pendry of Imperial College London and experimenters David Schurig and David Smith, who work in the electrical and computer engineering department at Duke University in Durham, North Carolina. In May, the team showed that, in principle, it’s possible to ferry electromagnetic waves such as light around an object by surrounding it with a “metamaterial”: an assemblage of tiny rods and C-shaped rings (Science, 26 May, p. 1120). The waves would then pass as if the object weren’t there, rendering it invisible.
The electromagnetic waves cause the electrons in the rings and rods to slosh, and the sloshing, in turn, affects the speed at which the waves travel through the material. If the speed varies in the right way within the cloak, the waves will curve around the object. The theory predicts only how the speed of the waves must vary; it leaves it to experimenters to design the material.
When Schurig, Smith, and colleagues worked out the details, they found that their two-dimensional device required only C-shaped copper rings nestled side by side. The team also simplified the parameters specified by the theory. The changes made the metamaterial easier to build but also left the cloak slightly reflective, as the team reports online this week in Science. “The goal of this paper was to demonstrate that we more or less have the mechanism and that we can design the materials to the parameters,” Schurig says.
Before we dictate surrender terms there remain a few kinks to work out:
The cloak is hardly perfect: Instead of an all-concealing sphere, it’s a ring that works only for microwaves zipping along in a plane. The microwaves must also be polarized perpendicular to the plane. And even then, the cloak reflects some of the waves and casts a slight shadow.
Keep an eye on this technology. Metamaterials only appeared on the scene a short time ago and already they have what essentially amounts to a working cloaking device. That is a staggering rate of technological progress, and suggests a major potential for good minds with decent funding (metamaterials will soon join carbon nanotubes in research grant nirvana) to make major leaps in concept and implementation.
More here, where comments suggest that the tech may be well known in the defense community.