What consumes only 9 watts of power and is at 40 kHz?
Well, I think we would all agree that this sounds just like an acoustic tractor beam. Unfortunately it can’t grab onto Romulan battle cruisers or interstellar Ferengi cargo ships because it is acoustic, and other than Battle Star Galactica, there is no sound in space. (The producers of BattleStar Galactica felt that the “whoosh” of a space ship as it passed by added to the effect. Star Trek producers also made this same decision, but I have it on good authority from Howard Walowitz, astronaut, that there is no sound in space).
I have written on a similar technology in the past (January 2014) but in that case small objects were lifted and moved around by situating them in the nodes of standing wave patterns. This approach appears to be much more versatile with more potential applications.
A group of British university researchers, led by PhD graduate student Asier Marzo, from Universities in Bristol and in Sussex, used high frequency (40 kHz) and high amplitude sound waves to grab hold of, and manipulate, polystyrene (e.g. Styrofoam) spheres as large as 4 mm in diameter. Their work was published in Nature Communications in October 2015. And like the acoustic levitation work report above, they used a large number of miniature loudspeakers- 64 to be specific to generate what they called an “acoustic hologram”. This is a metaphor comparison since technically a hologram is a photonic or light based phenomenon, but with the correct acoustic control, similar results can be obtained…we do live in exciting times!
But unlike the previous acoustic levitation work cited above, this acoustic hologram, or acoustic tractor beam, can manipulate and control the objects with very fine detail. To date, acoustic holograms have been developed that can have a tweezer-like shape, an acoustic vortex that can trap and manipulate an object at the base, and a high-intensity acoustic cage that can precisely move an object around.
Future work is being planned on being able to manipulate objects as large as beachballs from 10 meters away, but Asier Marzo and his colleagues are more interested in manipulating very small objects such as miniature capsules of medicine and, perhaps nano-technological, medical devices. Marzo and his colleagues see this as a potential technology to assist astronauts in space, experiments that occur under the water, and most importantly, in the human body- surgery will sound controlled devices that can be moved inside the body during surgery without surgical incisions.
And 40kHz at high sound levels may sound to be dangerous, but ultrasonics- sounds above 20 kHz- have been well-studied over the years. The potential danger of ultrasonics will be the subject of part 2 of this blog series.
