# Visualising invisibility

##### Jul 31, 2006

Invisibility has been an ingredient of myths, novels and films for millennia – from Perseus versus Medusa in Greek legend to James Bond’s latest car and Harry Potter’s cloak. A new study published today by the Institute of Physics reveals that invisibility is closer than we think.

The paper, Notes on conformal invisibility devices, published in the New Journal of Physics describes the physics of several theoretical devices that could create the ultimate illusion – invisibility.

“Objects are visible because they reflect light rays” says author Dr Ulf Leonhardt at St Andrews University, Scotland. “To be invisible, an object would have to let light pass through it, like H. G. Well’s Invisible Man. Alternatively light would have to bend around an object for it to be invisible. The ideas in this paper are based around devices that will bend light or radio waves around a hole inside the device. Any object placed inside the hole will become invisible. The light would flow round the hole like water around an obstacle.”

The bending of light is the cause of many optical illusions, such as mirages in the desert. Light bends in the hotter air near the ground in the desert and this causes a reflection of the sky on the ground – a mirage.

Dr Leonhardt went on to say “The devices work by bending light, as in a mirage. However, a mirage involves the reflection of light which produces the shiny image that can be seen: an invisibility device bends light without producing an image. To do this, the devices must have carefully designed refractive index profiles. The paper explains the physics and mathematics behind the devices using images rather than complex equations: it visualizes invisibility.”

The refractive index is a measure of the optical length that light has to travel in a medium: the higher the refractive index, the longer the optical path is to the light ray. Light rays bend when the refractive index of the medium they are travelling through varies. According to Fermat’s Principle of optical paths, light will follow the shortest optical path length. In the case of the mirage, air closer to the desert ground is hotter and has a lower refractive index than the cooler air higher up. Therefore light bends close to the desert floor in order to stay in the lower refractive index region.

Dr Leonhardt added “The next step is actually making one of these theoretical devices. There are advances being made in metamaterials that mean the first devices will probably be used for bending radar waves or the electromagnetic waves used by mobile phones. Such devices may be useful in wireless technology, for instance in protecting sensitive electronics from mobile-phone radiation in airplanes. After these have been developed, it is possible that devices that work for visible light are not too far behind.”

Source: Institute of Physics

Explore further: Heat makes electrons spin in magnetic superconductors

## Related Stories

#### New 3-D imaging technology for living cells

Mar 09, 2015

The major limitation of microscopy is light itself: if we want to see an object smaller than the wavelength of visible light, we cannot use conventional optics. When it comes to imaging cells, the problems ...

#### New flexible films for touch screen applications achieve longer lasting display

Mar 05, 2015

Today, touch screens are everywhere, from smart phones and tablets, to computer monitors, to interactive digital signage and displays. Many touch screens are made of layered thin (billionths of a meter thick) ...

#### Flexible nanosensors for wearable devices

Feb 25, 2015

A new method developed at the Institute of Optoelectronics Systems and Microtechnology (ISOM) from the Universidad Politécnica de Madrid (UPM) will enable the fabrication of optical nanosensors capable of sticking on uneven ...

#### Igniting the air for atmospheric research

Feb 18, 2015

Scientists from Vienna and Moscow have created a high-energy mid-infrared laser powerful enough to create shining filaments in the air. Such devices could be used to detect chemical substances in the atmosphere.

#### Engineering discovery brings invisibility closer to reality

Jan 26, 2015

Since the beginning of recorded time, humans have used materials found in nature to improve their lot. Since the turn of this century, scientists have studied metamaterials, artificial materials engineered ...

#### First-of-its-kind tube laser created for on-chip optical communications

Jan 23, 2015

(Phys.org)—Nanophotonics, which takes advantage of the much faster speed of light compared with electrons, could potentially lead to future optical computers that transmit large amounts of data at very ...

## Recommended for you

#### Heat makes electrons spin in magnetic superconductors

Apr 24, 2015

Physicists have shown how heat can be exploited for controlling magnetic properties of matter. The finding helps in the development of more efficient mass memories. The result was published yesterday in Physical Review Le ...

#### Portable MRI could aid wounded soldiers and children in the third world

Apr 23, 2015

Scientists at Los Alamos National Laboratory are developing an ultra-low-field Magnetic Resonance Imaging (MRI) system that could be low-power and lightweight enough for forward deployment on the battlefield ...

#### Examining Einstein—precise experiments using lasers in space

Apr 23, 2015

Tests carried out in zero-gravity on board the FOKUS research rocket. Successful demonstration of technology for the QUANTUS mission.

#### ICARUS neutrino experiment to move to Fermilab

Apr 23, 2015

A group of scientists led by Nobel laureate Carlo Rubbia will transport the world's largest liquid-argon neutrino detector across the Atlantic Ocean from CERN to its new home at the US Department of Energy's ...

#### National security on the move with high energy physics

Apr 23, 2015

Scientists are developing a portable technology that will safely and quickly detect nuclear material hidden within large objects such as shipping cargo containers or sealed waste drums. The researchers, led ...

#### Mechanical cloaks of invisibility—without complicated mathematics

Apr 23, 2015

A honeycomb is a very stable structure. If it has a larger hole, however, stability is largely lost. What might a honeycomb look like, which survives external forces in spite of a hole? Such stable types ...