A new form of computing: just add water
11 June 2015
Computers and water typically don't mix, but in bio-engineer Manu Prakash's lab at Stanford University, the two are one and the same.
Manu Prakash, an assistant professor of bioengineering at Stanford, and his students have developed a synchronous computer that operates using the unique physics of moving water droplets. Their goal is to design a new class of computers that can precisely control and manipulate physical matter.
The computer is nearly a decade in the making, incubated from an idea that struck Prakash when he was a graduate 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 says.
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," says Prakash. "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 information 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 current edition of Nature Physics.
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 information and utilize 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 synchronize all the droplets. The idea showed promise, and in the early stages of the project, Prakash recruited a graduate student, Georgios Katsikis, who is the first author of the Nature Physics paper.
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 realized that a rotating magnetic field might do the trick.
Katsikis and Prakash built arrays of tiny iron bars on glass slides, laid a blank glass slide on top and sandwiched a layer of oil in between. They then injected into the mix individual water droplets that had been infused with tiny magnetic nanoparticles.
Every time the field flips, the polarity of the bars reverses, drawing the magnetized droplets in a new, predetermined direction. Every rotation of the field counts as one clock cycle 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 synchronicity, 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," says 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 paper describes the fundamental operating regime of the system and demonstrates building blocks for synchronous logic gates, feedback and cascadability – hallmarks of scalable computation. A simple-state machine including 1-bit memory storage (flip-flop) is also demonstrated using the above basic building blocks.
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.
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.