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Artificial materials
15 or metamaterials
All things are artificial, for nature is the art of God
Sir Thomas Browne Religio Medici
15.1 Introduction
All the materials discussed so far were produced by nature. Well, not by nature
alone. We certainly helped nature here and there. We combined the elements
in a manner which led to a variety of new properties. We managed to persuade
some crystals to grow under circumstances where they were most reluctant to
do so. We produced structures with the thickness of a single atom, but we were
always restricted by the ways atoms were willing to arrange themselves. An
artificial material, on the other hand, may come about by taking an entirely
innocuous dielectric and immersing into it some small elements, and lo and
behold, its electrical behaviour radically changes. Alternatively, an artificial
material may just have a periodic structure made of dielectrics or metals.
The idea of producing artificial materials is not new. The first person who
Lippmann received the Nobel managed to do so was probably Gabriel Lippmann, who in 1894 produced
Prize in 1908. an artificial material by projecting an image upon a not too thin film of pho-
tographic emulsion. In contrast with the traditional methods of photography,
registering contrast, he developed the film in the form of a dielectric-constant
variation caused by standing waves due to reflection from the rear boundary of
the film. Since different colours have different wavelengths and since the stand-
ing waves due to those colours could be superimposed, Lippmann was able
to produce remarkably good colour photographs. The mechanism is clearly
Bragg reflection (although it was not called so at the time) due to the periodic
dielectric-constant variation.
A mere four years later, in 1898, Jagadis Chunder Bose proposed twisted
jute (see Fig. 15.1) as an artificial material. He showed that such a material
could rotate the polarization of an electromagnetic wave. We would call it
nowadays an artificial chiral material. After such a promising start, the next
half-century, as far as we know anyway, was a rather bleak one. Nothing
happened until the radomes of radars needed somewhat higher dielectric con-
stants than those easily available in natural materials. The solution was to create
artificial materials by inserting metallic pieces (rods, discs, or spheres) into a
very light dielectric. It was done quietly, without causing much excitement.
∗
∗ D. Walsh, ‘Artificial semiconductors’, As it happens, one of us also had some ideas concerning artificial ma-
Nature 243, 33–35 (1973). terials. The material here is a multilayered structure of alternate thin films
of metal and dielectric. The resulting potential diagram is then similar to the
