Years from now, this contraption will be on a museum shelf
labeled "Version 1". For now, I'll add it to my growing list of
"within 5 years........." that never seems to amount to anything.
Scientists have created a powerful acoustic weapon called a “sound bullet” that could help kill cancer cells and down hostile submarines in war.
Researchers at the California Institute of Technology created the weapon with inspiration from Newton’s cradle (see image below), that desktop toy comprised of a series of stainless steel balls suspended by fishing wire.
A team led by Caltech professor Chiara Daraio and Alessandro Spadoni designed a system of ball bearings that are controlled by weights. By varying the pressure on the bearings, researchers were able to amplify and focus sound waves until they were destructive.
Here’s how the system is constructed: researchers lined up 21 rows of stainless steel ball bearings in an area the size and shape of a laptop computer. They attached weights at each end to vary the pressure on each row.
Then the scientists dropped a small ball from a distance of eight inches into the ball bearings. Using a high-speed camera and a pressure sensitive metamaterial, the scientists observed pressure waves focus on a single spot several inches away.
That means the researchers were both able to focus sound waves on a specific target and amplify them more than 100 times more than had been previously accomplished with other metamaterials.
Though the pitch of the sound waves was beyond the audible range of humans, it could be tuned to project a brief, ear-splitting explosion of sound.
The utility of “sound bullets” versus normal ammunition is that sound can travel through liquids and solids as easily as they can air — meaning, for example, they could be far more useful than traditional torpedoes.
But it’s not just the military that benefits. Doctors could also use sound bullets to destory kidney stones or cancerous tumors without damaging surrounding tissue.
Turned down in intensity, they could also reveal to engineers structural weaknesses in buildings and bridges.
Those kinds of applications are still years away.
Their research was published in the Proceedings of the National Academy of Sciences.
