Posts Tagged ‘sound

Portable Acoustic Tractor Beam: build it at your home

leave a comment »


Written by physicsgg

January 14, 2017 at 10:19 am

Posted in mechanics

Tagged with

Soft-drink cans beat the diffraction limit

leave a comment »

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….. Read the rest of this entry »

Written by physicsgg

July 11, 2011 at 7:44 am

Posted in waves

Tagged with