"Sound Bullets" help military and hospitals

A group of researchers at Cal Tech found inspiration for "sound bullets" when observing a modified rendition of Newton's cradle (the contraption with stainless steel balls suspended by a wire that continues to hit back and forth for very long periods of time). They figured out a way to concentrate and amplify sound waves to make them a very destructive acoustic force (aka: "sound bullets"). The way they achieved this was by lining up 21 parallel rows of ball bearings, each with 21 bearings and weights attached, to vary the pressure in each row. They placed these rows on a created acoustic lens made from metamaterial. At one end they dropped a small ball causing compression to travel down the row in a wave.

The impressive part of this, is that once the first ball was dropped, and the compression wave traveled, the last ball did not carry the wave outward. Instead, the energy of the ball was passed into the metamaterial that focuses the waves to a spot on the acoustic lens a few inches away. On this spot, the group was able to focus all of the sound, thus amplifying the waves greater than 100 times more than what previous metamaterials have achieved in the past. The researchers say the numbers could be easily increased, amplifying it even more.

This means that we no longer have just lead bullets, but "sound bullets" that, unlike lead bullets, can travel through air, liquid, and solids the same carrying with them a devastating amount of energy. If sound bullets were to be turned to a weapon, they could shoot holes in submarines or reach into underground bunkers resulting in severe shock waves.

While the sound bullets could be used for weaponry, it could equally be used for medical and engineering purposes, helping structural engineers to see weak supports inside a structure or a doctor to image the body without resorting to high doses of radiation. Perhaps, in the future, sound bullets could destroy tumors by concentrating heat on malignant tissue under the skin.

The applications of this bullet are endless and open a new world to materials. This is interesting because not only is this break through helping the medical community but also engineering and military ones as well.

http://www.popsci.com/science/article/2010-04/sound-bullets-could-sink-subs-pummel-underground-bunkers-destroy-tumors