A Real Invisibility Cloak

[frank462]

Check this out: A Real Invisibility Cloak

Harry Potter fans take note: scientists have finally come up with a workable design for an invisibility cloak

Physicists figured out the complex mathematical equations for making objects invisible by bending light around them last year.

A group of engineers at Purdue University in Indiana have now used those calculations to design a relatively simple device that ought to be able to - one day soon - make objects as big as an airplane simply disappear.

 

[jimbob]

A group of engineers at Purdue University in Indiana have now used those calculations to design a relatively simple device that ought to be able to - one day soon - make objects as big as an airplane simply disappear.

For a restricted range of wavelengths...

It could be *quite* confusing I imagine:

Say you are invisible to red light, then HeNe laser ranging mightn't work on you, and people could see the red part of any image behind you, but also see you in yellow and green...

IRRC, these are called metamaterials, and are arrays of inductors, capacitors, and resistors, to make a material that seems homogenous at the wavelength of interest, and that has a negative permittivity and permiability at this wavelength.

These metamaterials are actually better at longer wavelengths, which might have significant applications, as it should be possible for microwave or milimetric radar.

I imagine that it would be difficult for visible wavengths.

 

[yairhol]

A small correction to Jimbob, invisibility in which this article refers to does not incorporate negative permittivity and permeability but rather positive permittivity and positive permeability. The permeability is controlled with metamaterials (SRRs or split ring resonators) and varies along the "cloak" in order to guide the electromagnetic radiation around the object. The SRRs vary in dimension. They do not affect the permittivity much only the permeability.
And as Jimbob has stated it is only for a narrow band of frequencies.

Regards,
Yair

 

[yairhol]

I imagine that it would be difficult for visible wavengths

You betcha as the SRRs would need to be very very small (tens of nanometers) in order to work at visible wavelengths. This is still technologically difficult to do as the SRRs would need to vary in dimensions in the order of parts of a nanometer.

Regards,
Yair

 

[rjh01]

Here is something from Scientific American Visible Light Bent the 'Wrong' Way

Everyone has seen a prism bend light. Now researchers have constructed a material that bends visible light in the opposite way. The odd effect, known as negative refraction, is similar to what is needed in far-out proposals for creating a cloak of invisibility. For now, however, the device only works in two dimensions, so construction of invisible spaceships will have to wait.

 

[yairhol]

The invisibility cloak was thought of after the negative refraction phenomenon had been established or even before that just after negative permeability had been demonstrated. In the negative refraction experiments, scientists had to set up negative permittivity and permeability which would be very close in values so that minimum reflection would take place because of unmatching between air and the material. After they convinced themselves that they could control the permeability as they like, they set up to design the cloaking device as this device relies on changes in permeability values. But as far as I know, the permeability values are positive (the permittivity is positive as well).

Regards,
Yair

 

[Mobyseven]

Currently only works for EM waves on the scale of microwaves, and only in two dimensions.

Ed knows what problems might arise trying to make anything invisible to visible wavelengths of light...

 

[Ex-drone]

This is not news. I have an invisibility cloak. I just can't remember where I put it down.