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.
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.
Nevertheless, scientists predict that metamaterials will make ‘invisibility’ possible for any object within the next decade. Interestingly, this technology could also create an EM ‘wormhole’: an invisible tunnel between two points in space. Pass an object into one end of it, and watch it disappear — and reappear out the other end. This could help in endoscopic surgeries where surgical instruments affect the intense magnetic fields of an MRI scanner, distorting MRI images. By passing tools through an EM wormhole, surgeons could hide them from the fields, allowing only their tips to be ‘visible’ at work!