Better sound images
Camouflaged kitten2
Invisibility cloaks still belong to the realm of science fiction, but it is a legitimate field of research which frequently catches the eye of mainstream media, who then spin the usual clichés about Harry Potter technology. If it became a reality and objects could be hidden from view, you would have to resort to more primitive methods of detection, such as prodding the object with a stick. You might even consider looking for it with sound, in the same way that sonar searches for submarines or images wrecks on the sea bed. Well guess what? Harry Potter magic may put an end to that too.
To achieve optical invisibility, light is made to flow around an object like water around a rock in a stream. None is reflected from the object and light from behind it passes to the front, giving the appearance that the object is not there. Scientists have made the necessary metamaterials that can produce this effect and have made small objects invisible to electromagnetic radiation within a narrow range of wavelengths. It would be like hiding a miniature version of Harry Potter, but only when he is illuminated by blue light, but not green or red. Most importantly, the concept works and these materials promise more than just better camouflage for the battle field. Metamaterials could provide us with super lenses, giving microscopes the capability of imaging well beyond the limits of conventional optics.
Sound waves are physical and are not part of the electromagnetic spectrum, but acoustic metamaterials could do with sound what their optical counterparts do with light. Nicholas Fang and his research team working at the University of Illinois, have recently produced a flat metamaterial lens which was capable of focusing ultrasound to an exceptionally small spot size1. It’s not yet achieving anything that cannot be done with conventional acoustics, but it lifts acoustic metamaterials from the books on theory and on to the lab bench. This science could one day provide improved imaging resolution for acoustic technology. In engineering it might detect otherwise hard to see cracks in buildings and other structures. In medicine, these metamaterials could provide major improvements for in vitro ultrasound imaging, seeing details inside the human body that are invisible to our technology today.
1) “Focusing Ultrasound with an Acoustic Metamaterial Network”, Shu Zhang, Leilei Yin, and Nicholas Fang, Phys. Rev. Lett. 102, 194301 (2009), DOI:10.1103/PhysRevLett.102.194301
2) Photo by Malingering (Creative Commons Attribution).
See also:
http://physics.aps.org/synopsis-for/10.1103/PhysRevLett.102.194301
http://news.illinois.edu/news/09/0624superlens.html
