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。 ) m: X, s! X$ m" K
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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; { j+ {: L) g7 s' \ The film contains tiny structures that together form a "metamaterial", which can, among other tricks, manipulate light to render objects invisible.1 ?1 H- F( ~ D' X
2 o. Q6 ?/ q+ I3 c$ ] Flexible metamaterials have been made before, but only work for light of a colour far beyond that which we see.
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9 M2 P, ~7 l3 _9 Y; P1 F Physicists have hailed the approach a "huge step forward".
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+ q( o5 U( U' x5 D The bendy approach for visible light is reported in the New Journal of Physics.
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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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; ~8 z, Q Y2 c8 q% {& E5 A 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.% ~& K5 [# ^' ^! R1 h
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Even flexible metamaterial films have been shown off for this high-wavelength range.
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For the far shorter waves we can see, a metamaterial requires structures so tiny - nanostructures - that they push the boundaries of manufacturing.
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2 y' d2 u; u* C, f' \8 r6 c "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.
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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."4 i3 F& l2 [6 H& ~
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So instead of building the typical stacks of the "fishnet" structures on hard, brittle silicon, Dr Di Falco used a thin polymer film. v j: @/ K7 @ l6 o6 k) `) ?
/ E# R# P& }" `& M "Typically what you do is stack several layers of fishnet structures and this all together will give you a metamaterial," Dr Di Falco explained.. j7 J% t9 W B3 n8 l" B) ^) W
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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."
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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".1 b1 e4 b9 W, S( Z$ H
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"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.: j$ s" |4 B; k; M* U: g& q
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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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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.
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"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." |