No strings attached, Chinese scientists have levitated small
live animals, including tadpoles, fish and spiders using ultrasound
for the first time ever.
Researchers at the Northwestern Polytechnical University in
Xi'an conducted the levitation experiment by employing an
ultrasound emitter and reflector to generate a sound pressure
field.
The emitter produced roughly 20-millimetre-wavelength sounds
which balanced the relevant gravity and therefore could levitate
objects half that wavelength or less in theory, Xie Wenjun, a
material physicist at the university who led the research, told
China Daily.
Xie and his colleagues reported their findings online on
November 20 in the US journal Applied Physics Letters.
Their work could help in the manufacture of medicines or
materials that requires a non-container environment.
The scientists started the experiment three years ago after
their previous success in levitating globs of the heaviest solid
and liquid iridium and mercury.
"Our aim is to find out how to process some metals without the
aid of containers," Xie said.
At times, compounds are too corrosive for containers to hold, or
they react with containers in other undesirable ways.
"When we wanted to further examine how to achieve better
stability of the levitated object, the wild idea of using live
animals came to us," the researcher said.
After the scientists had the ultrasound field in place, they
used tweezers to carefully place animals between the emitter and
reflector. It turned out that they could float ants, beetles,
spiders, ladybugs, bees, tadpoles and fish up to 1 centimetre in
midair.
When they levitated the fish, the researchers added water
through a syringe to the ultrasound field every minute to keep them
alive. "The water also levitated, spreading over the fish like a
thin film," Xie said.
The research required each levitation to last more than half an
hour. During the experiment, the animals looked agitated and tried
to escape from the field the ant tried crawling in the air and
struggled to break away by rapidly flexing its legs; and the
ladybug tried flying away.
"We had to control the levitation force carefully, because they
tried to fly away," Xie was quoted as saying in Live Science. "An
interesting moment was when my colleagues and I had to catch
escaping ladybugs."
The scientists measured the pressure on the levitated animal and
found it "much smaller than the gravity force it was under," said
Xie. "So we think it didn't do any harm to the object."
The technology of acoustic levitation can be traced back to
1866, when German physicist August Adolph Eduard Eberhard Kundt
invented the "Kundt's tube," a glass tube in which dust is shown to
collect at the nodes of standing waves, enabling the measurement of
sound velocity in gases and solids.
(China Daily December 15, 2006)