Fish-like sensors mimics lateral line

A PRESSURE sensor that mimics the way a fish's lateral line works could help submersible craft navigate.

The technology could improve underwater robots' ability to detect hazards, such as deep sea vents and shipwrecks, when the water is too murky for a camera to work effectively, or the object is too close for sonar, says Douglas Jones at the University of Illinois at Urbana-Champaign.

The lateral line is a sense organ that runs along the sides of most fish and enables them to detect changes in water pressure. This allows fish to sense depth and the direction of the current, and also means they can swim in synchronised schools even in darkness.

The line is peppered with hair cells called neuromasts that fire in response to pressure waves. The pattern of signals generated along the line allows the fish to pick out the tiniest flick of a nearby tail.

Jones, alongside Chang Liu at Northwestern University in Evanston, Illinois, made an artificial neuromast by adding boron to a 500-micrometre-long silicon hair to create a stress-sensitive resistor. As the hair bends in response to water motion, its resistance changes, allowing the force of the water's movement to be calculated.

The researchers tested the sensor by fixing an array around a plastic pipe and measuring the response to various objects placed in the water, including a live crayfish. The animal's wiggling legs generated a pattern of pressure signals that enabled the team to calculate its precise location in relation to the pipe. Because the hairs in the array are oriented at right angles to each other, the direction of the water motion can be easily determined (see diagram).

Finally, the distance to the object can be worked out in the same way a fish would, by moving water in the direction of the object and timing how long it takes to receive an echo (Bioinspiration and Biomimetics, DOI: 10.1088/1748-3182/5/1/016001). "We're hopeful it will be useful for making sure any underwater vehicle doesn't get trapped by unseen obstacles," says Jones.

"Anything that fortifies an undersea robot's sense of its environment, and its ability to avoid obstacles, is to be welcomed," says Andy Bowen of Woods Hole Oceanographic Institution in Massachusetts. Bowen designed Jason Junior, the remote-controlled robot sub that famously imaged the wreck of the Titanic in 1986. "In the search for new deep sea vents, I can imagine this artificial lateral line autonomously sensing a hydrothermal plume and using an on-board algorithm to home in on the source of it. It's a fascinating technology," he says.