Submarines Get Fish-like Sensors

March 12, 2007 — Thanks to a row of sensory organs along their sides, fish can avoid obstacles, swim in schools and seek prey, even in dark water. Now, inspired by those "lateral lines," researchers have developed an array of artificial sensors for underwater vehicles.

Equipped with an artificial lateral line, a submarine or submersible robot could potentially move through the water like a fish, detecting targets and avoiding collisions.

"We are trying to develop a new type of sensor for subs that can detect underwater events, currents and obstacles without conventional sonar and lights," said Chang Liu, professor of electrical and computer engineering at the University of Illinois, Urbana-Champaign.

Liu developed the technology with colleagues at the University of Illinois and Bowling Green State University.

Lights aren't very effective in murky water, said Liu, and sonar can give away the location of a sub that doesn't necessarily want to be noticed.

The lateral line Liu and his team developed consists of up to 16 tiny sensors less than a millimeter tall, arranged in a row that can be up to a few feet long.

The size of the sensors and the spaces between them match those found naturally in fish, and they are designed to detect changes in water pressure and movement.

The researchers affixed the artificial lateral line to a 3-foot-long submersible. As the sub moved through the water, it could detect the source of a vibrating object.

The sub zeroed-in on the object just like a fish might move toward a struggling fly on the water's surface.

The sub could also detect and track an underwater wake created by another object. In nature, some marine animals rely on the wakes of other fish as a kind of trail leading them to a destination.

"They seem to have done a good job of replicating what fish actually do," said Matthew McHenry, an assistant professor of ecology and evolutionary biology at the University of California, Irvine.

But, he added, that approach has limitations.

"If they directly try to copy what nature does, they are setting themselves up for failure," said McHenry. "There are constraints in engineers that nature doesn't have, and there are constraints in nature that engineering doesn't have."

Finding the happy medium between the two is the trick to bio-inspired design, he said.