# Visualising invisibility

##### July 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: Drones being honed to help farmers grow better crops

## Related Stories

#### Drones being honed to help farmers grow better crops

July 30, 2015

Farmers will be using drones in the near future to monitor and improve their crops to help feed a hungry world, say Texas A&M AgriLife Research scientists who are now developing the technology.

#### 'Plasmonic' material could bring ultrafast all-optical communications

July 30, 2015

Researchers have created a new "plasmonic oxide material" that could make possible devices for optical communications that are at least 10 times faster than conventional technologies.

#### Transforming living cells into tiny lasers

July 28, 2015

In the last few decades, lasers have become an important part of our lives, with applications ranging from laser pointers and CD players to medical and research uses. Lasers typically have a very well-defined direction of ...

#### Smaller, faster, cheaper: A new type of modulator for the future of data transmission

July 27, 2015

Transmitting large amounts of data, such as those needed to keep the internet running, requires high-performance modulators that turn electric signals into light signals. Researchers at ETH Zurich have now developed a modulator ...

#### Artificial moth eyes enhance the performance of silicon solar cells

July 23, 2015

Mimicking the texture found on the highly antireflective surfaces of the compound eyes of moths, we use block copolymer self assembly to produce precise and tunable nanotextured designs in the range of ~20 nm across macroscopic ...

#### Could your smartphone one day tell you you're pregnant?

July 1, 2015

Researchers at the Hanover Centre for Optical Technologies (HOT), University of Hanover, Germany, have developed a self-contained fiber optic sensor for smartphones with the potential for use in a wide variety of biomolecular ...

## Recommended for you

#### Tri Alpha Energy reportedly makes important breakthrough in developing fusion reactor

August 26, 2015

(Phys.org)—Science Magazine is reporting that physicists working at Tri Alpha Energy in Los Angeles have succeeded in building a device that held a ball of superheated hydrogen plasma for five milliseconds, longer than ...

#### Neural qubits: Quantum cognition based on synaptic nuclear spins

August 27, 2015

(Phys.org)—The pursuit of an understanding of the base machinery of the mind led early researchers to anatomical exhaustion. With neuroscience now in the throes of molecular mayhem and a waning biochemical bliss, physics ...

#### Evidence suggests subatomic particles could defy the standard model

August 27, 2015

The Standard Model of particle physics, which explains most of the known behaviors and interactions of fundamental subatomic particles, has held up remarkably well over several decades. This far-reaching theory does have ...

August 27, 2015

Physicists have found a radical new way confine electromagnetic energy without it leaking away, akin to throwing a pebble into a pond with no splash.

#### Seeing quantum motion

August 28, 2015

Consider the pendulum of a grandfather clock. If you forget to wind it, you will eventually find the pendulum at rest, unmoving. However, this simple observation is only valid at the level of classical physics—the laws ...

#### Antimatter catches a wave: Accelerating positrons with plasma is a step toward smaller, cheaper particle colliders

August 26, 2015

A study led by researchers from the U.S. Department of Energy's (DOE) SLAC National Accelerator Laboratory and the University of California, Los Angeles has demonstrated a new, efficient way to accelerate positrons, the antimatter ...