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The Harry Potter invisibility cloak just took another small step forwards

SNC121112_cloak_640.jpg.CROP.rectangle3-large.jpgMany of us dreamed as children of being able to make ourselves invisible.  We saw the movie about “The Invisible Man” and we looked at the jar of ‘vanishing cream’ on the dressing table.  Later children read Harry Potter or saw the movie.  Then in 2006 scientists demonstrated a small working model that hid a copper cylinder from microwaves.  The trick was a thin coating of metamaterials engineered for the purpose.  The problem was that it only worked for narrow bandwidths, and actually made objects more prominent at other wavelengths.  This applies to all so-called ‘passive’ cloaks.  They end up scattering more waves than are emitted by the object they are trying to hide.  You are adding matter, and that matter responds to electromagnetic signals.

The new approach, described in Physical Review Letters, pioneers an ‘active’ invisibility cloak using an ultrathin system that uses amplifiers to coat the surface of the object in an electric current.  The result is a cloak that can hide objects over a ‘broadband’ range of frequencies.  It uses energy (hence ‘active’), but achieves an invisibility over a spectrum range “an order of magnitude broader” than passive cloaks achieve.  We’re not there yet, but it’s a promising new approach.  The day will come when we’ll be able to switch it on and slip unseen out of tedious meetings….

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