Fish-like sensors for underwater robots

Today, both submarine and surface ships use sonar for navigation. But sonar and other vision systems face various limitations. So why not imitating fish? For millions of years, fish have relied on "a row of specialized sensory organs along the sides of their bodies, called the lateral line" to avoid predators or to find preys. So engineers at the University of Illinois at Urbana-Champaign (UIUC) have decided to build an artificial lateral line for submarines and autonomous underwater vehicles (AUVs). The first tests have been successful, and we can now envision a day where AUVs could detect and track moving underwater targets or avoid collisions with moving or stationary objects.

This technology has been developed by a team led by Chang Liu, professor of electrical and computer engineering at UIUC. Here is what he says about this new technology.

"Our development of an artificial lateral line is aimed at enhancing human ability to detect, navigate and survive in the underwater environment," said Liu. "Our goal is to develop an artificial device that mimics the functions and capabilities of the biological system."

Below is a picture showing a future model of autonomous underwater robot using a artificial lateral line (Credit: Chang Liu's team, UIUC). Here is a link to a larger version.

Fish have used this lateral line for millions of years to avoid predators or to find preys. But how can you build an artificial lateral line on submarines or underwater robots to do the same?

The artificial lateral line consists of an integrated linear array of micro fabricated flow sensors, with the sizes of individual sensors and spacings between them matching those of their biological counterpart.

To fabricate the tiny, three-dimensional structures, individual components are first cast in place on sacrificial layers using photolithography and planar deposition. A small amount of magnetic material is electroplated onto each of the parts, which are then freed from the substrate by an etchant. When a magnetic field is applied, the induced torque causes the pieces to rotate out of the plane on tiny hinges and lock into place.

Each sensor is integrated with metal-oxide-superconductor circuitry for on-chip signal processing, noise reduction and data acquisition. The largest array the researchers have built consists of 16 flow sensors with 1 millimeter spacing. Each sensor is 400 microns wide and 600 microns tall.

And does this work? The first tests have been successful, and "with further advances in engineering, man-made underwater vehicles should be able to autonomously image hydrodynamic events from their surroundings," Liu said.

This research work has been published by the Proceedings of the National Academy of Sciences under the name "Distant touch hydrodynamic imaging with an artificial lateral line" (Volume 103, Number 50, Pages 18891-18895, December 12, 2006). Here are two links to the abstract and to the full paper (PDF format, 6 pages, 2.40 MB).

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