META MATERIALS

ABSTRACT

Meta materials are artificial materials engineered to have properties that may not be found in nature. They are assemblies of multiple individual elements fashioned from conventional microscopic materials such as metals or plastics, but the materials are usually arranged in periodic patterns. Meta materials gain their properties not from their composition, but from their exactingly-designed structures. Their precise shape, geometry, size, orientation and arrangement can affect the waves of light or sound in an unconventional manner, creating material properties which are unachievable with conventional materials. These meta materials achieve desired effects by incorporating structural elements of sub-wavelength sizes, i.e. features that are actually smaller than the wavelength of the waves they affect

The primary research in meta materials investigates materials with negative refractive index Negative refractive index materials appear to permit the creation of super lenses which can have a spatial resolution below that of the wavelength. In other work, a form of 'invisibility' has been demonstrated at least over a narrow wave band with gradient-index materials. Although the first meta materials were electromagnetic acoustic and seismic meta materials are also areas of active research.

Potential applications of meta materials are diverse and include remote aerospace applications, sensor detection and infrastructure monitoring, smart solar

power management, public safety, radomes, high-frequency battlefield communication and lenses for high-gain antennas, improving ultrasonic sensors, and even shielding structures from earthquakes.

The research in meta materials is interdisciplinary and involves such fields as electrical engineering, electromagnetics, solid state physics, microwave and antennae engineering, optoelectronics, classic optics, material sciences, semiconductor engineering, Nano science and others

1. INTRODUCTION

The things which our eyes are not able to see are considered as “Invisible”. Light is neither absorbed nor reflected by the objects, passing like water flowing around a rock. As a result, only the light from behind the objects can be seen. The devices which are going to make us hide are invisibility devices. Researchers at the University of California at Berkeley, whose work is funded by the American military, have engineered materials that can control

light’s direction of travel. The world’s two leading scientific journals, Science and Nature, are expected to report the results in near future. . The concept of invisibility would involve surrounding the object by a

"meta material”. Meta-material is a type of composite material that has unusual electromagnetic properties. According to the researchers, light rays incident on the material would be bent around the object, only to emerge on the other side in exactly the same direction as they began. Although the work is only theoretical, the researchers reckon that materials invisible to radio waves could be produced within five years.

2. META-MATERIAL

The new "meta-materials," whose physical structure bends visible light in a way that ordinary materials don't, may help efforts to make an invisibility cloak that could guide light around an object so that neither a reflection nor a shadow would be created. Researchers have developed meta-materials that show these unusual light-bending abilities for other parts of the electromagnetic spectrum, notably for microwaves, but efforts to do this with visible light have been limited to flat, two-dimensional systems because the shorter the wavelength, as in visible light, the smaller the features of the man made metamaterial.

Figure 1. Bending of light in meta-material

There are some scientific catches that the tale-tellers never had to worry about:

For a total invisibility effect, the waves passing closest to the cloaked object would have to be bent in such a way that they would appear to exceed relativity's light speed limit. Fortunately, there's a loophole in Albert Einstein's rules of the road that allows smooth pulses of light to undergo just such a phase shift.

The invisibility effect would work only for a specific range of wavelengths. "There is a price to be paid if you want a thin cloak, in that

it operates only over a narrow range of frequencies," Pendry said.

The cloak could be made to cover a volume of any shape, but "you can't flap your cloak," Pendry said. Moving the material around would spoil the effect.

The tiny structures embedded in the metamaterial would have to be smaller than the wavelength of the electromagnetic rays you wanted to bend. That's a tall order for optical invisibility, because the structures would have to be on the scale of nanometers, or billionths of a meter. It's far easier to create radar invisibility, Pendry said: "You're talking millimeters" — that is, thousandths of a meter.

3. RESEARCH WORKS IN FIELD OF INVISIBILITY

3.1 Xiang Zhang

Xiang Zhang the leader of the researchers, said: “In the case of invisibility cloaks or shields, the material would need to curve light waves

completely around the object like a river flowing around a rock.”

Figure 2. Meta-material

An observer looking at the cloaked object would then see light from behind it – making it seem to disappear. Substances capable of achieving such feats are known as “meta-materials” and have the power to “grab” electromagnetic radiation and deflect it smoothly. No such material occurs naturally and it is only in the past few years that Nano-scale engineering, manipulating matter at the level of atoms and molecules, has advanced sufficiently to give scientists the chance to create them. The tiny scale at which such researchers must operate is astonishing in itself. Zhang’s researchers had to construct a material whose elements were engineered to within about 0.00000066 of a meter. The military funding that Zhang has won for his research shows what kind of applications it might be used for, ushering in a new age of stealth technology.

3.2 Researchers at the University of California

Researchers at the University of California at Berkeley, whose work is funded by the American military, have engineered materials that can control light’s direction of travel. The world’s two leading scientific journals, Science and Nature, are expected to report the results in near future.

3.3 Imperial College London

It follows earlier work at Imperial College London that achieved similar results with microwaves. Like light, these are a form of electromagnetic radiation but their longer wave-length makes them far easier to manipulate. Achieving the same effect with visible light is a big advance.

4. Cloak and shadow

This is a huge step forward, a tremendous achievement. It's a careful choice of the right materials and the right structuring to get this effect for the first time at these wavelengths. There could be more immediate applications for the devices in telecommunications. What's more, they could be used to make better microscopes, allowing images of far smaller objects than conventional

microscopes can see. And a genuine cloaking effect isn't far around the corner. "In order to have the 'Harry Potter' effect, you just need to find the right materials for the visible wavelengths," says Prof Hess, "and it's absolutely thrilling to see we're on the right track."

5. APPLICATIONS AND FUTURE PROSPECTS:

There'd be plenty of applications in the civilian world as well, even for rudimentary cloaking devices. For example, you could create receptacles to shield sensitive medical devices from disruption by MRI scanners, or build cloaks to route cellphone signals around obstacles.

Pendry's team proposed constructing all-over cloaking devices, the other research paper describes a simpler method that would involve shaping the meta-materials into cylindrical cloaking devices. The method could also work to block sound waves — like the cone of silence on the "Get Smart" TV show, but not as impractical.

6. Barrier in development of Invisibility devices:

Although we have thorough knowledge of theoretical concept

of invisibility but we have not enough practical implementation of these concepts.

Meta-material still needs more consideration and a lot has remained undiscovered and needs thorough study.

Security concern is another serious issue.

8. REFERENCES

Electronics for You, April, 2007Business week, August 5, 1996.

The New York times magazine, June, 2000.

Researchers from Duke University, USA

Researchers from imperial College London Findings of Xiang Zhang

Researchers at the University of California Imperial College London

www.Physicsworld.com www.Sciencedaily.com Science Reporter,april,2005