  Optical metamaterials capture the imagination with breathtaking promises of
nanoscale resolution in imaging and invisibility cloaking. We demonstrate an
approach to construct a metamaterial in which metallic nanorods, of dimension
much smaller than the wavelength of light, are suspended in a fluid and placed
in a nonuniform electric field. The field controls the spatial distribution and
orientation of nanorods because of the dielectrophoretic effect. The
field-controlled placement of nanorods causes optical effects such as varying
refractive index, optical anisotropy (birefringence), and reduced visibility of
an object enclosed by the metamaterial.
