AAWSAP DIRD, Invisibility Cloaking Theory and Experiments, March 2010

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Figure 10. Light Waves at Cloaking Device. Wave propagation in (a) virtual space and (b) real space.
This idea of cloaking by coordinate transformations was put forward by two
independent groups. Their theories appeared in Science Express on 25 May 2006 and
were published back to back in Science magazine later on. The first paper9 only
considered isotropic materials, optical materials where the speed of light at each point
is the same in each direction but may vary from point to point. Most natural optical
materials, except for some crystals and all liquid crystals, are isotropic. In isotropic
materials, invisibility is perfect only for light rays, but the cloaking device may cause
dislocations of light waves. In addition to the optical implementation of coordinate
transformations, some other tricks are required. The second paper10 considered
anisotropic materials for cloaking or other manipulations of electromagnetic waves.
Here, perfect invisibility is possible in principle (but not in practice, as is discussed
later). In October 2006, the first cloaking device was demonstrated, 11 for microwaves.
Science magazine regarded cloaking as one of the top 10 science breakthroughs of the
year (it was top in physics and engineering) . Scientific American listed the inventors of
cloaking devices-Sir John Pendry, David Smith, David Schurig, and Ulf Leonhardt­
among the top 50 policy, business, and research leaders of the year. The first paper12
on cloaking had initially been rejected by most major science and physics journals
before it finally appeared in Science, but since 2006, cloaking has become a
mainstream subject on which about a thousand papers have been published so far.
Metamaterials
The first prototype13 of a cloaking device was designed to operate in the microwave
region of the electromagnetic spectrum, for a wavelength of about 3 cm. The device
consists of 10 rings of flexible circuit board. The copper of the circuit board has been
etched away, apart from characteristic structures of about 3-mm size, so-called split­
ring resonators.
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