Washington DC
SOUND waves crammed with 1600 times more energy than ever before have been
bottled up by physicists in Virginia. They say the achievement, announced last
week at the Acoustical Society of America鈥檚 meeting in San Diego, will lead to
powerful machinery driven by sound.
Waves of sound behave in a similar way to waves on the beach. When a wave
contains too much energy it becomes too high and breaks. With sound, the
equivalent phenomenon is the formation of a shock wave, in which the energy
spreads over a wide band of frequencies and is lost as heat. Some energy from a
sound wave leaks into waves of higher frequencies, called overtones. A shock
wave is thought to form when these waves pile up at the same place, creating a
sudden change in pressure.
Advertisement
Tim Lucas and his colleagues at MacroSonix, a company in Richmond, Virginia,
realised that they could prevent this happening by tuning a cavity to damp down
the overtones. 鈥淵ou can control the shape of the wave with the shape of the
chamber,鈥� says Lucas. Using a cavity shaped liked an elongated pear, he has
achieved spectacular success. When this cavity is vibrated so that its walls
move back and forth over a distance of about 100 micrometres, it resonates with
a smooth, shockless wave of huge energy.
鈥淚t鈥檚 the equivalent of shaking a dishpan full of water and getting waves 40
centimetres tall,鈥� says Gregory Swift of the Los Alamos National Laboratory in
New Mexico. 鈥淚鈥檝e never seen anything quite this high before, and I鈥檓 quite a
fan of high-amplitude waves.鈥�
MacroSonix is now developing sound-driven machines, including an acoustic
piston that acts as a compressor. 鈥淲e have reached the power levels of machines
of the industrial revolution,鈥� says Lucas. 鈥淣ow we can replace those
machines鈥� and their moving parts鈥攚ith sound waves.鈥�