Original URL: http://www.theregister.co.uk/2010/06/03/microwave_blackness_dingus/

Artificial 'black hole' generator fashioned out of circuit boards

Radar-invisible stealth shed on horizon?

By Lewis Page

Posted in Science, 3rd June 2010 11:18 GMT

Chinese scientists have stunned the world of boffinry by fashioning an artificial "black hole" generator out of copper-coated circuit boards.

Disappointingly this is not a black hole in the normal sense of a universe-wrackingly dense lump of hypercompressed matter, exerting a gravitational pull so fearsome that not even light itself can escape - hence the blackness - of the sort which, some say, might be created by means of certain exotic experiments and then gobble up the entire Earth (and/or Moon and Sun) in a terrifying yet unambiguously newsworthy apocalypse incident.

No, this is a different kind of black hole altogether: but just like a proper black hole, electromagnetic radiation cannot escape from it. Technically it is referred to as an "omnidirectional electromagnetic absorber".

The device traps microwaves coming from all directions and "spirals" them in to its centre, converting them into heat with 99 per cent efficiency. Thus it is "black" in the microwave band - and its builders, Qiang Cheng and Tie Jun Cui of the State Key Laboratory of Millimeter Waves at Southeast University in Nanjing, believe that similar devices could be made to work in the visible spectrum also.

The absorber works using metamaterials, cunningly structured so as to bend electromagnetic waves in interesting ways. 60 concentric rings of copper metamaterial attached to circuit-board backing guide incoming microwaves into their centre. According to Cheng and Cui:

Since the lossy core can transfer electromagnetic energies into heat energies, we expect that the proposed device could find important applications in thermal emitting and electromagnetic-wave harvesting.

Other classes of theoretical metamaterials feature heavily in so-called "invisibility cloak" research, which would more correctly be described as the quest for an invisible shed. The black-hole omnisponge isn't of this type, however: it doesn't emit waves out again from its far side and so camouflage itself perfectly. Possible visual-spectrum successors would appear as a black blob to the human eye rather than being invisible.

However, Cheng and Cui's brainchild would be invisible viewed on radar - many types of which work in the microwave band. Pulses emitted by a scanner would not reflect from the omnisponge assembly to produce a blip on the screen: they would simply be absorbed and converted to heat, and the radar would be none the wiser as to the device's presence.

If the design can be turned into a practical coating that could be applied to aircraft, ships etc, far more stealthy stealth might soon be on offer. And in the field of undetectable sheds, it would at least be possible to build ones which didn't show up on radar - if not ones invisible to the naked eye.

It also seems worth noting that a device able to convert visible light into heat with high efficiency might seriously improve the performance of solar power apparatus.

The scientists' paper is published in the New Journal of Physics, and can be read for free here. ®