拥有《哈利波特》里的隐形斗篷是很多朋友的梦想,日前英国科学家的一项研究为这一切提供了可能。
* M2 J) R, f; s4 b8 \# ? Scientists in the UK have demonstrated a flexible film that represents a big step toward the "invisibility cloak" made famous by Harry Potter.
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The film contains tiny structures that together form a "metamaterial", which can, among other tricks, manipulate light to render objects invisible.
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Flexible metamaterials have been made before, but only work for light of a colour far beyond that which we see.; q! J9 w% w% r& S- R1 y' x
5 u* n/ c2 A( k; G$ w Physicists have hailed the approach a "huge step forward".7 `( x$ p' G3 }
# t5 {% f$ f6 J" K1 _8 ^6 f The bendy approach for visible light is reported in the New Journal of Physics.
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* _- ~2 n+ l% z5 T% }$ y4 r Metamaterials work by interrupting and channelling the flow of light at a fundamental level; in a sense they can be seen as bouncing light waves around in a prescribed fashion to achieve a particular result.
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But light waves can only be herded around by structures about the size of their wavelength - a property which is connected to their colour.
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Until now, the most striking demonstrations of invisibility have occurred for light waves with a much longer wavelength than we can see. This is because it is simply easier to construct metamaterials with relatively large structures.) Z( l2 {3 |2 i. ~4 D& s
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Even flexible metamaterial films have been shown off for this high-wavelength range.) F- Z7 Q3 F, z2 \7 g+ |
* f( y# [" w7 h; M! _* ^/ l For the far shorter waves we can see, a metamaterial requires structures so tiny - nanostructures - that they push the boundaries of manufacturing.; P: G8 c/ b- Y6 r5 \8 ~
) b4 W2 \* |3 {$ M "The first step is imagining first of all that this could be done," said Andrea Di Falco of St Andrews University, the author of the paper.: l( X4 T. ?' L6 P
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"All the typical results have been reached in flat and rigid surfaces because this is the legacy of the procedures used to create nanostructures."
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4 c5 @6 h3 u" T; N L* j So instead of building the typical stacks of the "fishnet" structures on hard, brittle silicon, Dr Di Falco used a thin polymer film.
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( L- W) \' H1 r6 H' n3 K1 o "Typically what you do is stack several layers of fishnet structures and this all together will give you a metamaterial," Dr Di Falco explained.
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"What I've done here is fabricate a single layer - I lift it off so that at the end I am left with a self-standing membrane - and show that it has the properties required to create a 3D flexible metamaterial."& o. m* g7 ^. l b
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Tents moment
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+ w: s: D* d% G Ortwin Hess, a physicist who recently took up the Leverhulme Chair in Metamaterials at Imperial College London, called the work "a huge step forward in very many ways".
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6 T% R! z4 N- H: t9 f9 E "It clearly isn't an invisibility cloak yet - but it's the right step toward that," he told BBC News.
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He added that the next step would be to characterise the way that the material's optical properties change as it is bent and folded.
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/ z$ ?; ~9 b5 E1 C o& k If the properties were sensitive to the movement, it may be useful for next-generation optics and lenses in, for example, handheld cameras.
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+ |3 B K( s! ^& w7 e v# u" W2 U& Z4 E If instead they were impervious to bending and motion, the invisibility cloak could be that much closer - but Professor Hess added that is still some way off.
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"Harry Potter has to wait still - that's the huge goal," he said.# o8 M; L+ v/ ]6 X9 e: [
+ v) R% u2 a0 ~2 I' V) [ "So far he's had to live in a house and now he can live in something like a tent; it's not the cloak that adjusts to his shape, but it's a bit more flexible. Now we have to take the next step forward." |