Robotic Ghost Knifefish

Researchers at Northwestern University have created a robotic fish that can move from swimming forward and backward to swimming vertically almost instantaneously by using a sophisticated, ribbon-like fin. The robot -- created after observing and creating computer simulations of the black ghost knifefish -- could pave the way for nimble robots that could perform underwater recovery operations or long-term monitoring of coral reefs. The black ghost knifefish, which works at night in rivers of the Amazon basin, hunts for prey using a weak electric field around its entire body and moves both forward and backward using a ribbon-like fin on the underside of its body. Observations revealed that while the fish only uses one travelling wave along the fin during horizontal motion (forward or backward depending on the direction on the wave), while moving vertically it uses two waves. One of these moves from head to tail, and the other moves tail to head. The two waves collide and stop at the center of the fin.

Researchers then created a computer simulation that showed that when these ‘inward counter propagating waves’ are generated by the fin, horizontal thrust is cancelled and the fluid motion generated by the two waves is funneled into a downward jet from the center of the fin, pushing the body up. The flow structure looks like a mushroom cloud with an inverted jet. The robot is also outfitted with an electro-sensory system that works similar to the knifefish's, and researchers hope to next improve the robot so it can autonomously use its sensory signals to detect an object and then use its mechanical system to position itself near the object. Humans excel at creating high-speed, low-maneuverability technologies, like airplanes and cars. But studying animals provides a platform for creating low-speed, high-maneuverability technologies -- technologies that don't currently exist. Potential applications for such a robot include underwater recovery operations, such as plugging a leaking oil pipe, or long-term monitoring of oceanic environments, such as fragile coral reefs.

More information:

http://www.sciencedaily.com/releases/2011/01/110119095045.htm