The jellyfish mimic moves with artificial muscles, whose core is made of nickel?titanium, which is a shape-memory alloy (a "memory metal" that remembers the shape at which it was cold-forged and will return to that shape). Most memory metals contract to their original shape when they encounter electric current, but this one contracts when heated. It does this through carbon nanotubes that are wrapped around the metal and coated with tiny platinum filaments. When the platinum filaments are exposed to hydrogen and oxygen gas, the platinum acts as a catalyst that drives the two gases to react and form water and heat. The heat makes the metal contract, causing the umbrella-like head of the jellyfish to deform and expel water from within the bell. That?s what propels the robot forward. Elastic material in the bell then pulls the "jellyfish head" back to its original position as it glides along.
"One beauty of this is that the only waste product is water," Tadesse says.
Currently the device is fueled by hydrogen and oxygen fed to it by large tanks in the lab. But that could change in the future. While the ocean is obviously home to lots of hydrogen and oxygen locked up in H20, there are also small concentrations of hydrogen and oxygen gas throughout the ocean, and it?s possible to create a device that could run on these and have a renewable fuel supply. Perhaps more feasibly, though, the robot could carry naturally occurring microbes that synthesize these gases. Those ideas are years in the future, Tadesse says. In the nearer term, prototypes could also be powered by small hydrogen-containing tanks of carbon nanotubes, or some sort of fuel cell.
Building biologically inspired robots is a growing trend. Recent prototypes have mimicked the movements of sharks, manta rays, roaches, and even fruit flies. So why jellyfish? For one, their propulsion system is pretty simple, Tadesse says. For another, jellyfish have few predators?getting your robot eaten by a shark would be costly, both for you and likely for the shark too. "We definitely don?t want it to be eaten," he says.
Another reason was the development of the artificial muscles by a group of researchers including some of the co-authors of the jellyfish robot study. That team detailed the muscle technology in a 2006 paper in the journal Science, but Ray Baughman of the University of Texas at Dallas, a co-author of the jellyfish study, says this is the first time the artificial muscles have been incorporated into a robot.
Baughman says the jellyfish robot and its kin could be a major improvement in ocean-going robots because bot builders face the same major problem as electric-car and smartphone builders: battery life. "The problem with electrically powered artificial muscles is that you don?t have enough energy density in a battery to power a robot for a significant amount of time," he says. But artificial muscles powered by energy stored in chemicals can last much longer. They are also stronger than the real thing; Baughman says that, weight for weight, the jellyfish?s artificial muscles can lift 500 times more than human skeletal muscles.
In the prototype jellyfish bot, all eight segments within the bell of the jellyfish rise and fall at the same time. That means it can move in just one direction: straight ahead. But the scientists are currently working on ways to deliver the fuel into each segment. "This should allow the robot to be controlled and moved in different directions," Tadesse says.
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