Portable Acoustic Tractor Beam: build it at your home



Soft-drink cans beat the diffraction limit

To focus sound to a point, all you need is a thirst for fizzy drinks.
Jon Cartwright

An acoustic lens made of soda cans can focus sound waves to a spot as small as 1/25th of a wavelength.

Sound, like light, can be tricky to manipulate on small scales. Try to focus it to a point much smaller than one wavelength and the waves bend uncontrollably — a phenomenon known as the diffraction limit. But now, a group of physicists in France has shown how to beat the acoustic diffraction limit — and all it needs is a bunch of soft-drink cans.

Scientists have attempted to overcome the acoustic diffraction limit before, but not using such everyday apparatus. The key to controlling and focusing sound is to look beyond normal waves to ‘evanescent’ waves, which exist very close to an object’s surface. Evanescent waves can reveal details smaller than a wavelength, but they are hard to capture because they peter out so quickly. To amplify them so that they become detectable, scientists have resorted to using advanced man-made ‘metamaterials’ that bend sound and light in exotic ways….. Continue reading Soft-drink cans beat the diffraction limit