Metamaterial cloaking
Metamaterials direct and control the propagation and transmission of specified parts of the light spectrum and demonstrate the potential to render an object seemingly invisible.
Metamaterial cloaking, based on transformation optics, describes the process of shielding something from view by controlling electromagnetic radiation.
Furthermore, permittivity and permeability are in a sense responses to the electric and magnetic fields of a radiated light source respectively, among other descriptions.
[5][13] Cloaking objects, or making them appear invisible with metamaterials, is roughly analogous to a magician's sleight of hand, or his tricks with mirrors.
Furthermore, the expanded optical powers presented in the science of cloaking objects appear to be technologically beneficial across a wide spectrum of devices already in use.
[14][15][25][26][27][28] One challenge up to the present date has been the inability of metamaterials, and cloaking devices, to interact at frequencies, or wavelengths, within the visible light spectrum.
The invisibility cloak deflected microwave beams so they flowed around the cylinder inside with only minor distortion, making it appear almost as if nothing were there at all.
The following is one of two studies accepted simultaneously by a scientific journal, as well being distinguished as one of the first published theoretical works for an invisibility cloak.
For example, a glass lens in a camera is used to produce an image, a metal cage may be used to screen sensitive equipment, and radio antennas are designed to transmit and receive daily FM broadcasts.
[2] Metamaterials were introduced about a decade ago, and these expand control of parts of the electromagnetic spectrum; from microwave, to terahertz, to infrared.
Theoretically, metamaterials, as a transmission medium, will eventually expand control and direction of electromagnetic fields into the visible spectrum.
Hence, a design strategy was introduced in 2006, to show that a metamaterial can be engineered with arbitrarily assigned positive or negative values of permittivity and permeability, which can also be independently varied at will.
Since these components are smaller than the radiated wavelength it is understood that a macroscopic view includes an effective value for both permittivity and permeability.
These materials usually gain their properties from structure rather than composition, using the inclusion of small inhomogeneities to enact effective macroscopic behavior.
As the elastic medium is distorted in one, or combination, of the described possibilities, the same pulling and stretching process is recorded by the Cartesian mesh.
The same set of contortions can now be recorded, occurring as coordinate transformation: Hence, the permittivity, ε, and permeability, μ, is proportionally calibrated by a common factor.
The second issue is that, while it has been discovered that the selected metamaterials are capable of working within the parameters of the anisotropic effects and the continual shifting of ε′ and μ′, the values for ε′ and μ′ cannot be very large or very small.
The scattering data of electromagnetic waves, after bouncing off an object or hole, is unique compared to light propagating through empty space, and is therefore easily perceived.
[9] Although mathematical reasoning shows that perfect concealment is not probable because of the wave nature of light, this problem does not apply to electromagnetic rays, i.e., the domain of geometrical optics.
The range of the refractive index of the dielectric (optical material) needs to be across a wide spectrum to achieve concealment, with the illusion created by wave propagation across empty space.
In stealth technology, impedance matching could result in absorption of beamed electromagnetic waves rather than reflection, hence, evasion of detection by radar.
[3][35][36] This demonstration, for the first time, of actually concealing an object with electromagnetic fields, uses the method of purposely designed spatial variation.
[3] A month prior to this demonstration, the results of an experiment to spatially map the internal and external electromagnetic fields of negative refractive metamaterial was published in September 2006.
[37] Employing this technique for this experiment, spatial mapping of phases and amplitudes of the microwave radiations interacting with metamaterial samples was conducted.
This is due to the random scattering of light, such as that which occurs in clouds, fog, milk, frosted glass, etc., combined with the properties of the metatmaterial coating.
As noted above, the original cloak demonstrated utilized resonant metamaterial elements to meet the effective material constraints.
Many scientific institutions are involved including:[citation needed] Funding for research into this technology is provided by the following American agencies:[48] Through this research, it has been realized that developing a method for controlling electromagnetic fields can be applied to escape detection by radiated probing, or sonar technology, and to improve communications in the microwave range; that this method is relevant to superlens design and to the cloaking of objects within and from electromagnetic fields.
[9] On October 20, 2006, the day after Duke University achieved enveloping and "disappearing" an object in the microwave range, the story was reported by Associated Press.
[49] Media outlets covering the story included USA Today, MSNBC's Countdown With Keith Olbermann: Sight Unseen, The New York Times with Cloaking Copper, Scientists Take Step Toward Invisibility, (London) The Times with Don't Look Now—Visible Gains in the Quest for Invisibility, Christian Science Monitor with Disappear Into Thin Air?
"[51] In November 2010, scientists at the University of St Andrews in Scotland reported the creation of a flexible cloaking material they call "Metaflex", which may bring industrial applications significantly closer.
