Not seeing is believing

Scientists predict that metamaterials will make ‘invisibility’ possible for any object within the next decade, writes Prakash Chandra.

The idea of turning invisible with the swish of a cloak has always fascinated sci-fi writers and scientists alike. Researchers at the University of Maryland have now made this a reality by using plasmon technology. We usually see an object when light strikes it and is reflected into our eyes. Under precise circumstances, light hits a metallic surface to create tiny, rapid electron waves called plasmons that can be made to carry much more information than is possible with conventional electronics. The Maryland team’s cloak uses a transparent acrylic plastic layer of two-dimensional patterns of concentric rings on gold film.

HT Image

The different refractive (bending) properties of plastic and gold let the cloak ‘negatively’ refract plasmons striking it, making light move around it — like water in a stream flowing around a rock. To an observer, it reflects nothing, making the cloak (and its contents) ‘invisible’.

You’ll still need to be a Harry Potter though, to walk around ‘unseen’ in this cape. For plasmon technology taps a limited range of the visible spectrum, and only in two dimensions. To steer light in 3D, you have to control it electromagnetically. Physicists from the University of Liverpool recently achieved this with metamaterials — composite materials that bend electromagnetic (EM) radiation like visible light around a spherical space. Objects within this space do not refract light and remain ‘invisible’. But the catch is that it works only for solid objects with fixed structures. Even slight deviations from its specifications cause the ‘invisibility’ to break down. So humans and animals would be spotted when they make sudden moves.