Page 112 - Maxwell House

92 Chapter 2

Meanwhile, the most stunning application of metamaterials is their ability to remake Harry
21
Potter’s legendary invisibility cloak. Figure 2.8.5 illustrates this cloaking effect. The metallic
sphere in this figure is surrounded by DNG metamaterial. The metamaterial bends EM, light,
heat or sound waves (shown as the black rays) around the sphere that emerge on the other side
in the same shape and direction as they began. Thereby, the reflection from the body is
minimized or eliminated. As such, the
sphere does not emit back EM waves,
light or sound and thus becomes
invisible or inaudible for an observer.
We recommend the reader to visit the
22
website and watch the awesome video
clip demonstrating the effect of
invisibility. Evidently, the role of the
sphere in Figure 2.8.5 may play, for
example, a military aircraft or tank
covered by the metamaterial layer, a
soldier in special “stealth” uniform that
makes him invisible on the battlefield, a
speeding car invisible and unheard for
the police inspector, etc. There are some
ideas how to bend in the same manner
the seismic vibrations around buildings Figure 2.8.5 Metallic sphere buried in
thereby protecting them against the metamaterial
earthquakes. A group of scientists in
Germany has successfully created a thermal cloak/barrier, preventing some area from heating
by bending the infrared wave flow around the protected area.

It is worthwhile to point out that the possibility of making metallic objects invisible for radar
signals was discovered and proved experimentally by Russian scientist O. N. Tereshin and the
th
group of its follows in 1970 [2]. Their approach was based on unique impedance structure
placed on the bodies’ surface that can be considered as a metamaterial prototype. Engineers are
now creating metamaterials with what is called a dynamic response, meaning their properties
vary depending on how much electricity is passing through them, or what light is aimed at them.
For example, a dynamic metamaterial filter might allow passage of light in the near infrared,
until electricity is applied. At which point, it lets through the only mid-infrared light. This ability
to "tune" the responsiveness of metamaterials has great potential for future applications.

For many years, the opinion prevails that no such metamaterials can be obtained with naturally
occurring materials. However, in 2007 Andrei Pimenov of the Universität Würzburg along with
his colleagues claimed that they have found the first naturally occurring metamaterial, the
metallic ferromagnet La2/3Ca1/3MnO3, that demonstrates the negativity of dielectric and
magnetic constant simultaneously. The reader may turn to the original publication [1] for the
details.

21 Public Domain Image, source: http://topsy.one/hashtag.php?q=%23metaMaterials
22 We recommend the reader to visit the website https://www.youtube.com/watch?v=Alrn1YUGuv4 to
watch the impressive video clip demonstrating the effect of invisibility.