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 A team from the universities of Bristol and Sussex, in conjunction
with Ultrahaptics, a spin-off set up by Sussex Professor of
Informatics, Sriram Subramanian, used high-amplitude soundwaves to
generate an acoustic hologram that can pick up and move small
objects.
Their research, led by PhD student Asier Marzo, was published in
Nature Communications in October.
The device allows the manipulation of small spherical objects in
mid-air by individually controlling 64 miniature loudspeakers to
generate the acoustic hologram without physical contact. The
loudspeakers are controlled at a frequency of 40 kilohertz (Khz),
creating high-pitched and high-intensity sound waves to levitate
spherical, expanded polystyrene beads of up to 4 millimeters in
diameter.
The tractor beam surrounds the balls with high-intensity sound to
create a force field that can keep the beads in place, move them or
rotate them.
 "What we have here is what we call an acoustic hologram - or what we
have called an acoustic hologram because I think it's the first time
it has been used," Marzo told Reuters. "A traditional hologram it's
made of light and you have flat surfaces. Nonetheless it creates a
3D light field. If you remember Star Wars you can see the robot R2D2
and it's broadcasting a 3D spaceship, even from a flat surface. So
this is exactly the same; we have a flat surface and we are creating
a 3D acoustic field that can surround the particle."
The concept of tractor beams grabbing and lifting objects was
created by science-fiction writers, but in recent years various
teams of scientists have sought to create an actual version.
Previous examples of tractor beam technology have involved using
light. According to Marzo, "I think the only real tractor beam that
has been achieved before was with light; it was a very powerful
focalized laser and it was able to trap the particles and move it
towards the laser, towards the source. However, the particles had to
be very small - like around the micrometers and you need to pump a
lot of power into the laser. So this is the real first acoustic
tractor beam and it's nice because acoustic tractor beam, acoustic
manipulation, needs much less power and it's more powerful in terms
of the materials that it can trap."
Marzo believes the new technique could be developed for many
applications. The team is certainly thinking big.
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He said: "Basically one of our future projects aims at levitating
something that's like a beachball ten meters away and we think this
could be very useful for zero gravity environments, like under water
or in the International Space Station. If you check videos
everything is floating around, water the nuts, screws, everything is
adrift uncontrollably, so if you can create fake gravity with this
device it would help a lot the astronauts."
A sonic production line could potentially transport delicate objects
and assemble them, without physical contact. But the Bristol
researcher's main goal is the revolution of surgery, with a
miniature tractor beam transporting drug capsules or microsurgical
instruments through living tissue.
"For me the major application, the best application, would be going
smaller and levitating things inside your body and this could be
drug capsules, this could be kidney stones, this could be clots or
micro surgical instruments, a tiny scalpel, tiny scissors that you
could control from the outside without any incision," said Marzo.
The team has used three different shapes of acoustic force fields to
work as tractor beams. Firstly, an acoustic force field that
resembles a pair of fingers or tweezers; the second an acoustic
vortex in which objects become trapped at the core, while the third
they describe as a "high-intensity cage" that surrounds the objects
and holds them in place from all sides. Each system consumes just
nine Watts of power.
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reserved.]
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