From clay to metamaterials
Since the dawn of civilization man has transformed the materials found in nature in materials that best suit your needs.With not everything can be baked or broiled over an open fire, he created clay pots and other ceramic artifacts to make your life easier. And if leaves and branches are not very durable, and cut stones is very laborious, he created tiles and bricks to build their homes.
They are all artificial materials, metamorphosed by the hand of man, but the prefix meta has only been added very recently, when the springs metamaterials began to translate not only into mechanical changes, but changes in the electromagnetic properties compared to natural materials.In this search for new features, soon appeared that the chemical elements of the Periodic Table were no longer sufficient.
The man began to build meta-atoms and assemble them in metamoléculas to make metamaterials that perform functions that no natural material can.Initially with invisibility cloaks , metamaterials soon proved capable of altering not only the electromagnetic waves – light and magnetism – but any type of wave -sound waves , sea waves and even seismic waves .
These materials are so artificial that already represent a promising field of research truly seething, something that can be illustrated by a sampling of the achievements in the area occurred only in recent weeks.
Metamaterial controlled by light
Despite the wonders achieved with metamaterials, unthinkable a few years ago, the manipulation of the waves that these materials are capable of doing is an intrinsic characteristic of each of them according to your design.
Thus, they work continuously, lacking a kind of on / off switch.
No more missing.
Ilya Shadrivov, Australian National University, created a metamaterial whose effect on electromagnetic waves is controlled by another external electromagnetic wave – a single beam of light emitted by anLED .
To demonstrate its new concept, the Australian team created a metamaterial that manipulates light like a normal plane mirror.
But controlled by an external beam of light, he starts to act like a concave mirror and a convex mirror or with no change in its format.
The meta-metamaterial atom of controlled light is a ring resonator (SRR: split-ring resonator ), a small ring that does not close completely, together with a varactor, an electronic component with variable capacitance, also known as varicap.
Changes in the varactors induce a shift in the resonance of SRR, changing the way it interacts with light or electromagnetic radiation in general – it could be a beam of microwave, for example.
The staff varactor each connected to a photodiode, so that each artificial atom can be controlled by an LED installed at his side.
Thus, the control that the metamaterial is about electromagnetic waves can in turn be controlled by varying the brightness of the LEDs.
Of the meta-atoms for metamolecules
Xiang Zhang, Laboratory Berkeley, United States, took a step forward in the “chemistry” of metamaterials.
Moreover, their metamaterial is also controlled by light.
A multi-institutional team has created not meta-atoms, but metamoléculas, whose behavior is a similarity in the chirality of molecules called natural – the direction to the right or to the left of each molecule.
The breakthrough is that metamoléculas can have their chirality changed rapidly from one version “right hand” conformation to a “left-handed” using only one light shooting.
Right-handed and left-handed versions of molecules – called enantiomers – may have radically different properties.
“Natural materials can be induced to change their chirality, but the process, which involves structural changes in the material, is weak and slow. With our artificial molecules, we demonstrated a switching of chirality strong, dynamic and high speed,” said Zhang .
The metamoléculas emit terahertz radiation beams. When they are powered by a light beam, they reverse their chirality changing the polarization of the waves emitting a process that can be done and reversed at will.
The metamoléculas are formed by a pair of meta-atoms 3D tapes made of gold, both with opposite chirality, which preserves the chirality mirror.
The “chemical bonds” this meta-molecule are made using silicon wafers, introduced at different points of each meta-atom, breaking the mirror.
The silicon wafers function as optoelectronic switches which invert the chirality of metamolécula when they receive a light beam.
The researchers say that the principle can be applied dynamically to reverse other electromagnetic properties of metamaterials.
Reactions between meta-atoms
Boris Lukyanchuk and colleagues from the Institute AStar, Singapore also worked with metamoléculas.But they went further, and formed their metamoléculas not just one type, but of two different types of meta-atoms.The first “meta-element” is a sphere of silicon, placed alongside one other type of meta-atom, most well known resonant ring made of copper.
The researchers studied the mutual influence of these two meta-atoms on the magnetic component of electromagnetic waves that should be handled by the metamaterial – a property known as magnetization.“When the two structures are separated by more than a micrometer, both act to strengthen the local magnetic field,” explained Lukyanchuk.
When they are approximated, however, begin to interact, resulting in the decrease of magnetization of the ring resonator, the point of becoming negative separations less than 0.5 micrometer.This is an artificial reproduction of something similar to what happens in natural materials, when a material becomes a ferromagnet with all the atoms contributing to their magnetizing “in the same direction” on the contrary, when the material regions have opposite magnetization, it becomes an antiferromagnet.
“We demonstrate that our hybrid networks metamoléculas present a distance-dependent magnetic interaction, opening new avenues for the artificial manipulation of antiferromagnetism in materials with low loss,” he said.
Metamaterials can also be quantum, as demonstrated Didier Felbacq and Mauro Antezza, University of Montpellier, France.Not satisfied with negative index of refraction , invisibility cloaks, superlens and even with plasmonics , they demonstrated that metamaterials can give a degree of freedom quantum.Unlike an artificial material with quantum properties , demonstrated for about a year, the two researchers have proposed two techniques to create a metamaterial with quantum properties.
The first uses meta-atoms as artificial crystals of ordinary atoms, ultracold organized periodically by optical traps, essentially creating a Mott insulator .Although there are no obstacles to its construction, the apparatus is somewhat complex, requiring precise conditions of the laboratory, which opens a few possibilities for practical use.
The second technique is much more promising, meta-atoms nanowire containing quantum dots.
“This structure is interesting for several reasons: it is simple, has many interesting properties (negative index, magnetism effective camouflage fully dielectric) and can be performed experimentally very easily,” say the researchers.
This area of research is still very new, which makes it difficult to predict its practical implications on the field of metamaterials.
However, as the quantum phenomena of matter allowed all the natural development of electronics, you can have the quantum metamaterials a glimpse of the vast possibilities of using the “artificial material” that scientists are creating.