MAR 04, 2014 12:00 AM PST

Amazonian Fish Inspires Better Underwater Robotics

WRITTEN BY: Jen Ellis
The black ghost knifefish of the Amazon basin takes advantage of its adaptations in several ways that are interesting-not just to the casual reader, but also to scientists interested in developing new automated underwater vehicles.

Knifefish use a small electric current as their navigation system (a process known as electrosensing). By producing a weak electric field around itself, a knifefish can detect objects and prey through sensing tiny perturbations in the electric field (thought to be as small as 0.1% of the total electric field that the fish emits). Therefore, it doesn't need to be able to see its prey and can successfully navigate and hunt at night or in turbid water.

This ability would be useful in underwater vehicles, which currently either rely on visual systems or radar/sonar for navigation. Navigation limitations and larger sizes make it difficult for existing vehicles to get close to aquatic life, and also make them difficult to maneuver around inanimate objects in tight spaces (such as a shipwreck) or in unclear and muddy waters.

Another useful adaptation is the ribbon-like fin found on the underside of the knifefish, allowing it to swim in multiple directions. This provides uncommon agility that would be extremely useful in an underwater vehicle. The knifefish is capable of rapid reversals of direction, rolls, and other close-proximity maneuvers necessary to capture escaping prey. In the language of robotics, this "omnidirectional mechanical capability" would greatly enhance the capability of any underwater vehicle.
A research group from Northwestern University has been studying the black ghost knifefish and its adaptations for some time in order to integrate these capabilities into a new generation of underwater vehicles. Such an autonomous vehicle would be able to easily handle situations that are too dangerous or impractical for divers, such as inspection of sunken vehicles on the ocean floor. The team presented their findings to the AAAS (American Association for the Advancement of Science) during their February 2014 meeting in Chicago.

The group has run multiple simulations to understand the mechanics of both the sensing and the propulsion system of the knifefish, and they have developed a series of underwater robots to test out their theories. Through this work, they have been able to establish mathematical relationships between some of the more fundamental properties, such as the propulsion output compared to amplitude and frequency of traveling waves.

Many challenges remain in translating knifefish capabilities to underwater robotic technology. For example, the knifefish maintains some continuity to its electric field and signal changes throughout the complex movements needed to catch prey. This allows it to understand its position to the prey and is achieved through omnidirectional sensing (similar to the omnidirectional mechanical capability). Setting up an electrosensing system without blind spots or disproportionate responses is no easy feat in an underwater vehicle (not to mention the body and fin construction needed for the mechanical component).

Even so, the Northwestern team has made great strides in characterizing the knifefish properties in terms that can be translated to underwater vehicles, and it's possible we will be seeing a new generation of underwater robotic vehicles in the not-too-distant future based on this technology. The knifefish would probably be proud.
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