On the fundamental flaws of cloaking by metamaterials

Invisibility cloaking, using metamaterials, excites the scientific community, the general public, amateurs of sci-fi and most importantly the funding agencies. If you think about it, it is indeed mind-boggling to be able to realize a Harry Potter type cloak!

The metamaterials community, in particular John Pendry and Ulf Leonhardt have thought and pioneered the first invisibility schemes by using metamaterials. The first demonstration of the invisibility cloak was demonstrated by David Smith's group. And subsequently, several researchers have been actively working (both theoretically and experimentally) on cloaking.

Funding agencies and the general public assume that we're close to cloaking military tanks, fighter airplanes, etc... And accordingly, with this type of technology, we could effortlessly win the war in Afghanistan or any war for that matter!

Well the reality is far from our wild imagination! Cloaking by using metamaterials suffer from two fundamental flaws:

1. We can only cloak objects which are of the same size as the wavelength of light.

For instance a typical human eye will respond to wavelengths from 400nm to 600 nm or so (+/- a few nm of course). It means that if you want to cloak an actual object from humans, it cannot be larger than 600 nm!!! This implies that using metamaterials, we can only cloak nanometer size objects, and if you think about it, these objects are so tiny that they are already cloaked!

2. Metamaterials cloaks are extremely sensitive to loss.

In theory, we can design lossless materials where the cloak works out of the box. But in the real world, we have to use materials which are lossy (suffer from energy dissipation). Thus, realistic materials will kill the cloak! However, in the future, we will be in a position to develop robust gain compensation schemes to compensate for losses.