Computing with water
Engineers have developed a computer that operates
using the unique physics of moving water droplets. The device could enable bulk
lab testing with each drop representing a test tube
Computers and water typically don't mix, but in Manu Prakash's lab
at Stanford, the two are one and the same.
Prakash and his students have built a computer that operates using
the unique physics of moving water droplets.
The computer was incubated from an idea that struck Prakash when
he was a student. The work combines his expertise in manipulating droplet fluid
dynamics with a fundamental element of computer science an operating clock.
“In this work, we finally demonstrate a synchronous, universal
droplet logic and control,“ Prakash said. Because of its universal nature, the
droplet computer can theoretically perform any operation that a conventional
electronic computer can crunch, although at significantly slower rates. Prakash
and his colleagues, however, have a more ambitious application in mind.
“We already have digital computers to process information. Our
goal is not to compete with electronic computers or to operate word processors
on this,“ Prakash said. “Our goal is to build a completely new class of
computers that can precisely control and manipulate physical matter.Imagine if
when you run a set of computations that not only data is processed but physical
matter is algorithmically manipulated as well. We have just made this possible
at the mesoscale.“
The ability to precisely control droplets using fluidic
computation could have a number of applications in high-throughput biology and
chemistry, and possibly new applications in scalable digital manufacturing. The
results are published in the journal Nature Physics.
THE CRUCIAL CLOCK
For nearly a decade since he was in graduate school, an idea has
been nagging at Prakash: What if he could use little droplets as bits of infor
mation and utilise the precise movement of those drops to process both
information and physical materials simultaneously. Eventually, Prakash decided
to build a rotating magnetic field that could act as clock to synchronise all
the droplets. The idea showed promise, and in the early stages of the project,
Prakash recruited Georgios Katsikis, the first author on the paper.
Computer clocks are responsible for nearly every modern
convenience. Smartphones, DVRs, airplanes, the Internet without a clock, none
of these could operate without frequent and serious complications. Nearly every
computer program requires several simultaneous operations, each conducted in a
perfect step-bystep manner. A clock makes sure that these operations start and
stop at the same times, thus ensuring that the information synchronises.
A MAGNETIC CLOCK
Developing a clock for a fluid-based computer required some
creative thinking. It needed to be easy to manipulate, and also able to
influence multiple droplets at a time. The system needed to be scalable so that
in the future, a large number of droplets could communicate amongst each other
without skipping a beat. Prakash realised that arotating magnetic field might
do the trick.
Katsikis and Prakash built arrays of tiny iron bars on glass
slides that look something like a Pac-Man maze. They laid a blank glass slide
on top and sandwiched a layer of oil in between.Then they carefully injected
into the mix individual water droplets that had been infused with tiny magnetic
nanoparticles.
Next, they turned on the magnetic field. Every time the field
flips, the polarity of the bars reverses, drawing the magnetized droplets in a
new, predetermined direction, like slot cars on a track. Every rotation of the
field counts as one clock cycle, like a second hand making a full circle on a
clock face, and every drop marches exactly one step forward with each cycle.
A camera records the interactions between individual droplets,
allowing observation of computation as it occurs in real time. The presence or
absence of a droplet represents the 1s and 0s of binary code, and the clock
ensures that all the droplets move in perfect synchrony, and thus the system
can run virtually forever without any errors.
“Following these rules, we've demonstrated that we can make all
the universal logic gates used in electronics, simply by changing the layout of
the bars on the chip,“ said Katsikis. “The actual design space in our platform
is incredibly rich. Give us any Boolean logic circuit in the world, and we can
build it with these little magnetic droplets moving around.“
The current chips are about half the size of a postage stamp, and
the droplets are smaller than poppy seeds, but Katsikis said that the physics
of the system suggests it can be made even smaller.Combined with the fact that
the magnetic field can control millions of droplets simultaneously, this makes
the system exceptionally scalable.
“We can keep making it smaller and smaller so that it can do more
operations per time, so that it can work with smaller droplet sizes and do more
number of operations on a chip,“ said graduate student and co-author Jim
Cybulski. “That lends itself very well to a variety of applications.“
Prakash said the most immediate application might involve turning
the computer into a high-throughput chemistry and biology laboratory. Instead
of running reactions in bulk test tubes, each droplet can carry some chemicals
and become its own test tube, and the droplet computer offers unprecedented
control over these interactions.
MM13JUN15
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