  A method is proposed to create materials with a desired refraction
coefficient, possibly negative one. The method consists of embedding into a
given material small particles. Given $n_0(x)$, the refraction coefficient of
the original material in a bounded domain $D \subset \R^3$, and a desired
refraction coefficient $n(x)$, one calculates the number $N(x)$ of small
particles, to be embedded in $D$ around a point $x \in D$ per unit volume of
$D$, in order that the resulting new material has refraction coefficient
$n(x)$.
