'Cloaking' device uses ordinary lenses to hide objects across range of angles

September 27, 2014
A multidirectional `perfect paraxial’ cloak using four lenses. From a continuous range of viewing angles, the hand remains cloaked, and the grids seen through the device match the background on the wall (about 2 m away), in color, spacing, shifts, and magnification. Credit: J. Adam Fenster / University of Rochester

Inspired perhaps by Harry Potter's invisibility cloak, scientists have recently developed several ways—some simple and some involving new technologies—to hide objects from view. The latest effort, developed at the University of Rochester, not only overcomes some of the limitations of previous devices, but it uses inexpensive, readily available materials in a novel configuration.

"There've been many high tech approaches to cloaking and the basic idea behind these is to take light and have it pass around something as if it isn't there, often using high-tech or exotic materials," said John Howell, a professor of physics at the University of Rochester. Forgoing the specialized components, Howell and graduate student Joseph Choi developed a combination of four standard lenses that keeps the object hidden as the viewer moves up to several degrees away from the optimal viewing position.

"This is the first device that we know of that can do three-dimensional, continuously multidirectional cloaking, which works for transmitting rays in the ," said Choi, a PhD student at Rochester's Institute of Optics.

Many cloaking designs work fine when you look at an object straight on, but if you move your viewpoint even a little, the object becomes visible, explains Howell. Choi added that previous can also cause the background to shift drastically, making it obvious that the cloaking device is present.

In order to both an object and leave the background undisturbed, the researchers determined the lens type and power needed, as well as the precise distance to separate the four lenses. To test their device, they placed the cloaked object in front of a grid background. As they looked through the lenses and changed their viewing angle by moving from side to side, the grid shifted accordingly as if the cloaking device was not there.  There was no discontinuity in the grid lines behind the cloaked object, compared to the background, and the grid sizes (magnification) matched.

The Rochester Cloak can be scaled up as large as the size of the lenses, allowing fairly large objects to be cloaked. And, unlike some other devices, it's broadband so it works for the whole visible spectrum of light, rather than only for specific frequencies.

Their simple configuration improves on other cloaking devices, but it's not perfect. "This cloak bends light and sends it through the center of the device, so the on-axis region cannot be blocked or cloaked," said Choi. This means that the cloaked region is shaped like a doughnut. He added that they have slightly more complicated designs that solve the problem.  Also, the cloak has edge effects, but these can be reduced when sufficiently large lenses are used.

In a new paper submitted to the journal Optics Express and available on arXiv.org, Howell and Choi provide a mathematical formalism for this type of cloaking that can work for angles up to 15 degrees, or more.  They use a technique called ABCD matrices that describes how light bends when going through lenses, mirrors, or other optical elements.

While their device is not quite like Harry Potter's , Howell had some thoughts about potential applications, including using cloaking to effectively let a surgeon "look through his hands to what he is actually operating on," he said. The same principles could be applied to a truck to allow drivers to see through blind spots on their vehicles.

Howell became interested in creating simple cloaking devices with off-the-shelf materials while working on a holiday project with his children. Together with his 14 year-old son and Choi, he recently published a paper about some of the possibilities, and also demonstrated simple cloaking with mirrors, like magicians would use, in a brief video.

The video will load shortly

To build your own Rochester Cloak, follow these simple steps:

  1. Purchase 2 sets of 2 lenses with different focal lengths f1 and f2 (4 lenses total, 2 with f1 focal length, and 2 with f2 focal length)
  2. Separate the first 2 lenses by the sum of their focal lengths (So f1 lens is the first lens, f2 is the 2nd lens, and they are separated by t1= f1+ f2).
  3. Do the same in Step 2 for the other two lenses.
  4. Separate the two sets by t2=2 f2 (f1+ f2) / (f1— f2) apart, so that the two f2 are t2 apart.
For their demonstration cloak, the researchers used 50mm achromatic doublets with focal lengths f1 = 200mm and f2 = 75mm. Credit: University of Rochester

Explore further: New invisibility cloak hides objects from human view

More information: arxiv.org/abs/1409.4705

Related Stories

New invisibility cloak hides objects from human view

July 27, 2011

For the first time, scientists have devised an invisibility cloak material that hides objects from detection using light that is visible to humans. The new device is a leap forward in cloaking materials, according to a report ...

'Metascreen' forms ultra-thin invisibility cloak

March 25, 2013

(Phys.org) —Up until now, the invisibility cloaks put forward by scientists have been fairly bulky contraptions – an obvious flaw for those interested in Harry Potter-style applications.

Two independent teams build heat cloaking device

February 10, 2014

(Phys.org) —Two teams, both in Singapore have created two different types of thermal cloaking devices. In their papers, both published in Physical Review Letters, the teams describe how they went about creating their devices ...

Recommended for you

Quest to find the 'missing physics' at play in landslides

August 30, 2016

During the 1990s, Charles S. Campbell, now a professor in the Department of Aerospace and Mechanical Engineering at the University of Southern California, began exploring why large landslides flow great distances with apparently ...

Invisibility cloak with photonic crystals

August 30, 2016

Almost as elusive as unicorns, finding practical materials for invisibility cloaking is challenging. Michigan Technological University researchers have new ideas how to solve that.

3 comments

Adjust slider to filter visible comments by rank

Display comments: newest first

gwrede
5 / 5 (3) Sep 27, 2014
Calling this setup a Cloaking Device is downright childish.

Sometimes I wish the whole concept didn't exist in fairy tales and fiction. Then we could see scientists do real work instead.
wal_reis
5 / 5 (2) Sep 27, 2014
It seems that this is a device for those who don't want to see something, and not for those who want not be seen. A good start. it's perhaps useful to hide things like pollution, waste and whatever is allegedly a cause of global warming. :)
kochevnik
not rated yet Sep 27, 2014
Hyperbolic geometry? Seriously? Maybe for a Disneyland exhibit

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.