Engineered metamaterials expand views on electromagnetismThursday, February 11th, 2010 by Antonio Manzalini
Metamaterials are artificial materials proving properties which are determined not only by the atomic composition but also by the inner structure, which is properly engineered (e.g. by inclusion of small inhomogeneities, or by integration of electric and magnetic micro resonators, etc.) to tailor certain macroscopic properties (basically the refractive index).
In optics, the refractive index is defined by the ratio between the speed of light in vacuum and the speed of an electromagnetic plane wave in the medium. As we may remember, from Maxwell’s equations the refractive index is given by the square root of the product of dielectric permittivity ε(ω) and the magnetic permeability μ(ω).
Research in metamaterials started by developing materials with negative refractive index (a property not found in any known natural material), that is engineering dielectric permittivity ε(ω) and the magnetic permeability μ(ω) of materials. Cutting-edge applications include invisibility cloaking for military applications, perfect lens for super-resolution imaging (that enables imaging with sub-wavelength image resolution), ultra-small waveguides, solid-state THz phase modulators, etc. Recently, the growing degree of control permittivity and permeability functions has fuelled an explosion of novel device ideas for remote aerospace applications, sensor detection and infrastructure monitoring, smart solar power, public safety, high-gain antennas, advanced memory devices.
As an example, recently NIST, Boeing and the University of Arizona have shown that transmission antennas can use metamaterials to enable their antenna to radiate as if they were as much as 50 times larger—theoretically capable of shrinking a full-size 150-mm cell phone antenna down to just 3 mm. In tests at 300MHz (requiring ordinarily a meter-size antenna) researchers were able to demonstrate almost 95 percent of full-size performance from a Z-shaped antenna just 30 mm square. Next, the researchers plan to field-test real antennas using their metamaterial-powered designs, with funding from the Defense Advanced Research Projects Agency (DARPA).
Let me conclude with something that sounds even more exotic: surprisingly, they say that metamaterials can allow also mimicking celestial mechanics ! Einstein’s general theory of relativity establishes equality between matter–energy density and the curvature of space-time. The metric has exactly the same effect on light as a refractive index. So they argue that it is possible to model the effect of powerful gravitational fields on light by creating the appropriate refractive materials in the laboratory.