|
Astronauts onboard the International Space
Station are studying strange fluids that might one day flow in the
veins of robots and help buildings resist earthquakes.
by Dr. Tony Phillips and Patrick
L. Barry
If you don't see it for yourself, you
might not believe it.
A gray blob oozes down the side of
a laboratory beaker. It's heading for the table, but before it gets
there a low hum fills the air. Someone just switched on an electromagnet.
The goop stiffens, quivers, then carries on oozing only after the
hum subsides.
Is it alive?
No, just magnetized.
"We call them magnetorheological fluids - or 'MR fluids' for short,"
says Alice Gast, a professor of chemical engineering at MIT. "They're
liquids that harden or change shape when they feel a magnetic field."
You can make some of this exotic stuff at home.
Just mix some powdered iron filings with a thick liquid like corn
oil, and presto: a simple MR fluid. Hold a magnet nearby
and the bits of iron will line up end-to-end; they form a rigid
lattice that stiffens the mixture. Take the magnet away and the
fluid will relax again.
If you own a sports car or a Cadillac,
you might have MR fluids in your shock absorbers. The stiffness
of magnetic shocks can be electronically adjusted thousands of times
per second, providing a remarkably smooth ride. Similar but more
powerful devices have been installed at Japan's National Museum
of Emerging Science and China's Dong Ting Lake Bridge. They're there
to counteract vibrations caused by earthquakes and gusts of wind.
Motion damping is perhaps the most practical use
for MR technology today, but much more is possible. Says Gast: "There
are many potential applications that make these fluids very exciting."
For example, MR fluids flowing in the veins of robots might one
day animate hands and limbs that move as naturally as any humans.
Book makers could publish rippling magnetic texts in Braille that
blind readers could actually scroll and edit. It might even be possible
to train student surgeons using synthetic patients with MR organs
that flex and slice like the real thing.
There are many problems to solve before
such things are possible. How do you control a magnetic field and
deliver it with exquisite precision anywhere inside an MR fluid?
Researchers aren't sure - but that's another story. Equally important
are the inner workings of the MR fluids themselves. "We need to
learn much more about their basic physics," says Jack Lekan of NASA's
Glenn Research Center.
That's the goal of an experiment called
InSPACE now orbiting Earth onboard the International Space Station.
Gast developed InSPACE, short for "Investigating the Structure of
Paramagnetic Aggregates from Colloidal Emulsions," in collaboration
with scientists and engineers at the Glenn Research Center. Gast
is the principal investigator; Lekan is the project manager.
Image courtesy: Lord
Corporation
The Dong
Ting Lake Bridge in China is equipped with magnetorheological
motion dampers to counteract gusts of wind.
|
InSPACE will explore a curious phenomenon:
When some low-density MR fluids are exposed to rapidly alternating
magnetic fields, their internal particles clump together. Over time
they settle into a pattern of shapes that look a bit like fish viewed
from the top of a tank. Such clumpy MR fluids don't stiffen as they
should when magnetized.
The structure
of particles in an MR fluid gradually changes when an alternating
magnetic field is applied. The leftmost picture shows an
MR fluid after 1 second of exposure to a fast-changing magnetic
field. The suspended particles form a strong, fibrous network.
The pictures to the right show the fluid after 3 minutes,
15 minutes and 1 hour of exposure. The particles have formed
clumps that offer little structural support.
|
The fish tank pattern is fragile and
takes about an hour to fully develop. It doesn't occur in MR fluids
that are constantly mixed and agitated, as in a car's suspension,
but it could prove troublesome in other situations.
The pull of gravity on Earth can distort the pattern - a
frustration to scientists trying to study its underlying physics.
That's why Gast and colleagues have sent their MR fluids to orbit.
On the space station, astronauts can expose a weightless (freely-falling)
fluid to magnetic pulses and record what happens.
"Astronauts are an integral part of our study,"
notes Lekan. They will reach into the Microgravity Science Glovebox,
where the experiment is located, to align and focus cameras on a
spot only 0.2 mm wide. If a fluid bubble gets in the way of the
shot ... flick! they can remove it.
more
A prototype
MR washing machine
|
In early April 2003, ISS Science Officer
Don Pettit conducted the first experiments with MR fluids inside
the glovebox. His two-hour "run" marked beginning of the InSPACE
investigation, which will likely continue off and on throughout
the month.
Meanwhile, some companies are already forging ahead
with new magnetorheological devices. Lord Corporation of North Carolina,
for example, is designing an MR washing machine. Magnetic dampers
inside the machine will decrease noise and vibration - and save energy.
They're also studying MR technology for seat belts and airbags in
cars. Because MR fluids can generate large forces quickly and flexibly,
they could be used by automakers to adjust the arresting force of
a seatbelt to the size and weight of a passenger.
Saving lives and silencing washing
machines - and that's just the beginning. Not bad for a bunch of
gray oily goop.
|
