New Invisibility Cloaking Device Thinner, Less Lossy

A new design for a cloaking device surmounting some of the limitations of existing “invisibility cloaks” has been developed by electrical engineers at the University of California, San Diego.

In the new study, the researchers designed a cloaking device that is both thin and doesn’t change the brightness of light around a hidden object. More applications than invisibility are in the future for the technology behind this cloak, for example concentrating solar energy and raising signal speed in optical communications.

Senior author Boubacar Kanté, professor in the Department of Electrical and Computer Engineering at the UC San Diego Jacobs School of Engineering, says:

“Invisibility may seem like magic at first, but its underlying concepts are familiar to everyone. All it requires is a clever manipulation of our perception. Full invisibility still seems beyond reach today, but it might become a reality in the near future thanks to recent progress in cloaking devices.”

The concept behind cloaking is to alter the scattering of electromagnetic waves, such as light and radar, off an object to make it less detectable to these wave frequencies.

But one of the drawbacks of cloaking devices is that they are typically bulky. First author Li-Yi Hsu, electrical engineering Ph.D. student at UC San Diego and the of the study, adds:

“Previous cloaking studies needed many layers of materials to hide an object, the cloak ended up being much thicker than the size of the object being covered. In this study, we show that we can use a thin single-layer sheet for cloaking.”

Their cloak, the researchers say, also overcomes another basic drawback of existing cloaking devices, being “lossy.” Cloaks that are lossy reflect light at a lower intensity than light hitting their surface.

“Imagine if you saw a sharp drop in brightness around the hidden object, it would be an obvious telltale. This is what happens when you use a lossy cloaking device,” said Kanté. “What we have achieved in this study is a ‘lossless’ cloak. It won’t lose any intensity of the light that it reflects.”

The researchers say that one of the keys to their cloak’s design is the use of non-conductive materials called dielectrics, which unlike metals do not absorb light. This cloak includes two dielectrics, a proprietary ceramic and Teflon, which are structurally tailored on a very fine scale to change the way light waves reflect off of the cloak.

“This cloaking device basically fools the observer into thinking that there’s a flat surface,” said Kanté.

L. Y. Hsu, T. Lepetit, and B. Kante,
Extremely thin dielectric metasurface for carpet cloaking
Progress In Electromagnetics Research, Vol. 152, 33-40, 2015

Illustration: The reflection pattern from an uncloaked object on a flat surface (top) compared to the reflection pattern of the same object covered with the cloaking device (bottom), which effectively mimics the reflection from a completely flat surface. Credit: Li-Yi Hsu/Jacobs School of Engineering/UC San Diego