Research engineers have reduced the losses and size associated with “invisibility cloaks.” According to the team, the cloaking device could have a number of applications, including concentrating solar energy and boosting optical communication signal speeds.
A significant issue with previous invisibility cloaks is the fact that they have low reflective efficiency. Cloaks that are “lossy” impact the ability of the device to reflect light. "Imagine if you saw a sharp drop in brightness around the hidden object, it would be an obvious telltale,” said Boubacar Kanté, a UC San Diego Electrical and Computer Engineering professor. “This is what happens when you use a lossy cloaking device. What we have achieved in this study is a [near] 'lossless' cloak.” This will ensure the light the device reflects is near the intensity it had when it encounters the cloak.
The reason many invisibility cloaks have low reflective efficiency is because they contain metal particles that are light absorbent. Instead, the team at UC San Diego used non-conductive dielectrics, which absorb a minimal amount of light. The dielectrics featured in the cloak include a proprietary ceramic and Teflon – both of which were manipulated to change the way light reflects off of the team’s technology. This thin matrix of Teflon, with cylindrical ceramic particles of varying sizes, was designed using electromagnetic simulation software.
"By changing the height of each dielectric particle, we were able to control the reflection of light at each point on the cloak," shared electrical engineering Ph.D. student Li-Yi Hsu. "Our computer simulations show how our cloaking device would behave in reality. We were able to demonstrate that a thin cloak designed with cylinder-shaped dielectric particles can help us significantly reduce the object's shadow."
Kanté and his team set out to address another key setback for these cloaks: bulkiness. "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," explained Hsu.
The engineers tested their design by creating a “carpet” cloak, which can mask objects sitting on flat surfaces. “This cloaking device basically fools the observer into thinking that there's a flat surface," said Kanté.
It does this by copying the reflection of light from the flat surface. According to the researchers, “any object reflects light differently from a flat surface, but when the object is covered by the cloak, light from different points is reflected out of sync, effectively cancelling the overall distortion of light caused by the object’s shape.”
"Invisibility may seem like magic at first, but its underlying concepts are familiar to everyone,” said Kanté. “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 group recently published a paper in the journal Progress In Electromagnetics Research. For more information, visit UC San Diego’s website.