Invisibility

//Has Harry Potter Met His Match?// **Invisibility** is no longer a mythical power possessed by super heroes and wizards. Modern day physics illuminates a whole new realm of possibilities regarding invisibility. Research done in the past decade at institutions such as Duke University and University of California, Berkley, has merely scratched the surface. Many associate invisibility with Harry Potter's Cloak, Frodo's Ring, or science fiction comic book heroes donning some article of clothing or object and instantaneously becoming invisible to the human eye. However, Invisibility is possible on many different levels of the spectrum. To make an object in other words "invisible" the waves must pass around it seamlessly essentially rendering it unseen. Researchers have gone about this using many different ways, attempting to create the most effective method. If scientists were truly able to make objects invisible from all angles, it would mean great breakthroughs for not just the military, but also the underlying science of metamaterial engineering.

1. Background 2. Metamaterials 3. Plasmonics 4. Holography and Optical Camouflage 5. The Fourth Dimension 6. Recent Innovations and Discoveries 6.1 Duke University 6.2 Japanese Invisibility Experiments 7. Future of Invisibility 7.1 Military 7.2 Earthquakes
 * Contents**


 * Background**

In everything from ancient mythology to modern science fiction, the ability to become invisible is associated with great power. So much power in fact, that the scenario of becoming invisible is used in literature to set the stage for honest people losing their sense morality and becoming criminals.

The modern understanding of light and electric fields began in the 19th century with numerous empirical experiments. No man excelled further in such hands-on investigations and description of physical phenomena than the great Michael Faraday. Faraday devised simple yet elegant experiments that allowed him to discover new characteristics about electricity, including that “electric fields could turn into magnetic fields and vice versa”(Kaku p.18). However, Faraday had almost no formal education, and while he could envision how the lines of magnetic force flowed, he could not begin to describe it mathematically.

James Clerk Maxwell, however, expertise was the opposite of Faraday’s. Maxwell was one of the great mathematicians of his age but had no background in experimentation. However, Maxwell realized that in Faraday’s meticulous observational descriptions was everything he needed to know to mathematically describe how electromagnetic magnetic fields behaved. He further hypothesized that constantly fluctuating fields would create waves of magnetic force. He was able describe this phenomena using only eight differential equations. When he calculated the speed of these waves, they came out to be almost exactly the same speed as the speed of light. So in 1864, he was able to conclude that light was a form of magnetic wave. Nearly every modern invention in electronics and optics has its roots in Faraday’s experiments and Maxwell’s equations, including all the research being done in the new field of metamaterials for use in invisibility.

Until recently, however, scientists have believed that real invisibility was basically impossible. But scientists have invented new kinds of optical materials that are very good at bending light and now there is a very active area of research in optics that focus on invisibility.

Yes, it’s true that for more than 100 years simple illusions done with mirrors have been able to conceal people. But a stage magician making a person in a big box “disappear” by putting an angled mirror in front of him is a long way from giving soldiers a means to be invisible on the battle field. Technically, the modern idea of real invisibility doesn’t mean just being camouflage or concealed, it means that something is effectively transparent so that what is behind it can still be seen.

To make a person invisible in this way, all the light coming towards you has to somehow be bent around you and then bent back and made to continue on in its original direction. One of the current “proof of concept” designs for such a device is a type of clear plastic cylinder with very thick walls. It looks very similar to a stack of new CD’s or DVD’s stacked on a spindle. No matter which direction light hits the curved sides of the cylinder, once it enters the plastic it curves around the open space in the middle ( where the spindle is - or where on a big cylinder, a person could be standing).


 * Metamaterials**

Scientists at the University of California, Berkeley have created a 3-D material that can reverse the natural direction of visible and near-infrared light. This development could lead to the development of cloaking devises that could conceal objects from the human eye.

Metamaterials are composite materials with the capability to bend electromagnetic waves. Metamaterials do this by altering how light normally behaves. For an invisibility cloak to be effective, the material must curve the light waves completely around the object. To successfully conceal an object, the metamaterials must have a negative refraction. For a metamaterials to have a negative refraction, its structure must be smaller than the electromagnetic wave being used.

Another approach scientists have taken is engineering a metamaterial to bend light backwards. Scientists have done this by growing silver nanowires inside permeable aluminum oxide. This extraordinary advancement is about 10 times thinner than a piece of paper. The vertical nanowires were designed to respond to the electrical field in light waves. This is a very innovative way to bend light backwards without attaining a negative refraction.

However, there are benefits to having a negative refraction that is found in the fishnet metamaterial. They improve performance by reducing interference and reversing the Doppler effect.

Both types of metamaterials will play an important role in optical imaging and cloaking devices. Though scientists believe these are extremely important discoveries, they deem that producing these materials on a large scale will be a challenge.




 * Plasmonics**

Plasmonics is the field of study of plasmons which are quanta of oscillating plasma. The oscillation represents a “quantum-mechanical density wave in the charge carriers in a substance such as a metal or semiconductor.” People routinely experience this phenomena as it is the basis for the color and reflective qualities of shiny metals. When light interacts with such materials, it causes a minute electric field which drives electrons back forth at the frequency of the light and the result is that the light will be reflected. However, there are frequencies that are outside the limits of particular materials and thus those frequencies are absorbed. Gold absorbs blue light but reflects low frequency red and yellow, forming its characteristic appearance.

Researchers in the field of Plasmonics are working to engineer nano-scale structures that create novel characteristics for manipulating light and electric fields. The range of possibilities go from new dyes and cosmetics to better ways to transfer data on a chip at the speed of optical signals while using metallic connections a small fraction of the size that would be required for a fiber optic connection. Another area is research is in the field of “invisibility.” To make an object effectively transparent, plasmonics can be used to develop metamaterials which have a negative refractive index, making it possible to bend light around and object so to conceal its presence.




 * Holography and Optical Camouflage**

[|Holograms] are a photographic or optical technology that can create images that can viewed from more than one perspective. It is relevant to one method of making a person appear invisible known as optical camouflage. Rather than trying to bend light around a person, camouflage attempts to make a person appear the same as the background. The patterns printed on the clothing worn by soldiers and hunters attempts to match typical backgrounds but of course every location will be slightly different. Optical camouflage attempts to solve that problem by using a camera to take a picture of the background and a video projector to shine that image on a person’s clothes or some type of screen. While this sounds somewhat complicated, it can actually work quite well as long as the people looking at the screen are only viewing it from one direction. As soon as they change perspective, the projected image will no longer match the background and the camouflage fails.

Holograms, because they show multiple perspectives, could potentially solve this problem. The challenge is that holographic technology requires far more sophisticated technology, particular for showing a changing image. Conventional holograms are typically made by first shining a laser through a beam splitter. Then one of the two beams shines on the object being recorded and the other is directed toward a special type of film. The reflected light from the first beam hitting the object also shines on the film. The two sources of light combine and an interference pattern is capture on the special film. By slowly rotating the object being photographic, the film can record an image from 360 degrees. To create an active or changing image, a computer is typically used to create and project hundreds of images a second, reflected in different directions. Technically this is quite different from the original hologram but the effect is the same.

Creating your own [|hologram] can help you understand the physics behind it.


 * The Forth Dimension**

The idea of invisibility expands from the world we know and live in to a realm scientists call the [|forth][|dimension]. Some physicists theorize that there are other dimensions beyond the one we live in, and it may be possible to temporarily move an object into another dimensional plane, rendering it invisible. Even if this highly hypothetical concept were true, current calculations indicate that it would require vastly more energy that any source we have available.


 * Recent Discoveries and Innovations**

//Duke University// Researchers at Duke University have made it possible to render on object invisible using "metamaterials" to cloak a small metal cylinder from passing microwaves. media type="youtube" key="Ja_fuZyHDuk" height="364" width="452"

//Japanese Invisibility Experiments// Many of the experiments aimed at developing technology that might be immediately useful are being done in Japan. Professor Susumu Tachi of Tokyo University developed an optical camouflage technique that comes close to simulating invisibility. They have assembled a device that uses a camera to capture a background image and then a project and imagine combiner to shine the background image on a highly reflective coat, similar to a movie screen. When you look at the person what you primarily see is a projected image of the background behind the person.

The Japanese researchers aren’t really interested in creating invisibility, rather they are looking at ways to “augment reality,” perhaps by projecting an CAT-scan image on a patient’s body during surgery so a doctor can see the body as if it were partially transparent. Another application might be for military pilots who could be allowed to “see through” the floor of their aircraft to look at the ground.

//Military// The military is a primary beneficiary from the recent discoveries made in metaphysics and invisibility. It is predicted that within in the next decade scientists will have successfully created an "invisibility suit." Made specifically with national defense in mind, soldiers wearing these suits render the ultimate camouflage. media type="youtube" key="Niz7Sdqu0jw" height="385" width="640"
 * Future of Invisibility**

//Earthquakes// The underlying research into invisibility has lead to focuses on the behavior of waves through various materials. Developing technology that bends light around and object to make it invisible has sparked interest in using the same concept to protect buildings from earthquakes. Earthquakes are felt in the form of seismic waves but such waves take different forms. Typically the most destructive type is the surface wave, which is similar to a wave on the water, and imparts oscillating horizontal displacement. Rather than bend waves of light, researchers are developing a building foundation that can bend the seismic waves around its structural footings. The mechanism would be a series of large concentric and interconnected plastic rings, each about 10cm thick and from about 1m to 10m across. The carefully engineered stiffness and elasticity of the rings would redirect the waves of vibration in an arc around the building’s footings. Obviously, the building doesn’t become invisible, but this research shows how a general idea in one field can inspire innovations in very different fields.

Sources

Harris, W, & Lamb, R. (n.d.). //How Invisibility cloaks work//. Retrieved from [] //Japanese scientist invents 'invisibility cloak'//. (2003, February 18). Retrieved from [] Kaku, M. (2008). //Physics of the impossible//. New York: Random House, Inc.. Yuka, Y. (2009, June 30). //Invisibility cloaks may shield buildings from earthquakes//. Retrieved from [] Zyga, L. (2007, August 22). //Scientists interpret physics behind invisibility cloaks//. Retrieved from []

Image Links

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