MOTION MOUNTAIN

images – transporting light 161
F I G U R E 110 An example of an isotropic metamaterial
(M. Zedler et al., © 2007 IEEE).
Ref. 123
Ref. 122
Ref. 124
Ref. 125
effect. However, these predictions have not been verified yet.
Most intriguing, negative index materials are predicted to allow constructing lenses
that are completely flat. In addition, in the year 2000, John Pendry gained the attention
of the whole physics community world-wide by predicting that lenses made with such
materials, in particular for a refractive indexn=−1, would be perfect, thus beating the
usual diffraction limit.This would happen because such a perfect lens would also image
theevanescent parts of the waves – i.e., the exponentially decaying ones – by amplifying
them accordingly. First experiments claim to confirm the prediction. Exploration of the
topic is still in full swing.
So far,left-handedmaterialshave been realized only for microwave and terahertz frequencies.
First claims in the visible domain have been published, but have to be taken
with care. It should be mentioned that one type of negative refraction systems have been
known since a long time: diffraction gratings. We could argue thatleft-handedmaterials
are gratings that attempt to work in all spatial directions. And indeed, all left-handed
materialsrealizedsofarareperiodicarrangementsofelectromagneticcircuits.
Metamaterials
Thesimplestrealizationofleft-handedsystemsaremetamaterials.Metamaterialsareengineered
metal-insulator structures with a periodicity below the wavelength of the radiation
for which they are designed, so that the structure behaves like a homogeneous
material. Metamaterials have negative or otherwise unusual permittivity or permeability
properties in a certain wavelength range, usually in the microwave domain; some
metamaterials areleft-handed.
Currently,therearetwobasicapproachestorealizemetamaterials.Thefirstistobuild
a metamaterial fromalarge array ofcompactresonantsubstructures,suchas inductorcapacitor(LC-)circuitsordielectricspheres.Thesecondapproachistobuildametamaterial
fromtransmissionlines. Thelatter approachhaslowerlossesandawiderspectral
range;anexampleforthistypeisshowninFigure110.Comparingandexploringdifferent
realizationsissubjectofintenseresearch.
Most metamaterials are conceived for microwaves or terahertz waves. Industrial applications
of metamaterials are expected for antenna design; for example, an antenna
dipole could be located just above a metamaterial and thus allowing to build flat direc-
Motion Mountain – The Adventure of Physics copyright © Christoph Schiller June 1990–November 2015 free pdf file available at www.motionmountain.net