Invisibility cloaks are making a splash. Or rather, preventing splashes, perhaps.
Although the science fiction idea of an invisibility cloak is a Harry Potter–style device that makes objects invisible to the eye, physicists have branched out. In addition to hiding objects from light waves under certain conditions (SN: 7/15/06, p. 42), researchers have made cloaking devices that can mask objects’ effects on other types of waves, including sound waves and water waves (SN: 5/18/13, p. 8).
Now, two teams of researchers have come up with ways of directing waves and currents around an object in a fluid, effectively hiding the object’s presence by cloaking its effect on the surrounding water. The techniques can also reduce drag or the rocking effect of waves on the object within the cloak, the scientists report in two studies in the Aug. 16 Physical Review Letters.
Whether for light, sound or water, such cloaks work by steering waves so they travel around an object rather than scattering off it, which would disrupt the waves’ paths and reveal the object’s presence. Instead, the cloak forces the waves to take a small detour around the object and return to the same configuration that they’d be if the object weren’t there. But “actually making these things is tricky,” says physicist John Pendry of Imperial College London, who was not involved with the studies.