London, Nov 5 : A team of US engineers has developed artificial hairs like those used by fish to sense water flow around them to avoid predators or take the most efficient path through complex turbulence, a move which could help improve robotic submarine maneuverability.
It's a well known fact that fish rely on more than just their eyes to navigate.
A prominent example is the cave-dwelling Mexican fish that has lost its eyes altogether, but can expertly navigate its environment using only an unusually sensitive lateral line - the sense organ that runs lengthwise down each side of a fish's body.
The lateral line consists of many sense organs called neuromasts, each with a number of microscopic hairs with a mucus cap, or cupula.
The nervous system can sense and interpret the movement of the hairs as they are bent by moving water.
According to a report in New Scientist, Michael McConney and Vladimir Tsukruk at the Georgia Institute of Technology in Atlanta, US, believe that autonomous underwater vehicles (AUVs) would benefit from their own lateral lines made up of hair-like sensors.
Working with Chang Liu's team at the Northwestern University in Illinois, they constructed 550-micrometer-long hairs from a common polymer.
These are mounted on a piezoelectric material that gives off a voltage when a water current deflects the hairs.
But, the "bare" hair sensor will only deflected by water flowing at speeds above 100 micrometers per second.
So, to increase sensitivity, the researchers used a gel to mimic the mucus cupula that caps the hairs in fish.
"The gel is used to connect the hair to the surrounding water, much like a wind sock," said Tsukruk. "It increases sensitivity by enhancing drag," he added.
The researchers coated the watery gel onto their artificial hairs using a.
Tests showed that the hydrogel-capped hair sensors could detect flow velocities of just 2.5 micrometers per second - 40 times more sensitive than without the gel.
The artificial sensors are around five times as long as those on fish, but that is an appropriate size for AUVs, which tend to be a few metres in length.
"As the size of the vehicle goes up, you need longer hairs because the thickness of the boundary layer increases," explained Tsukruk.
Gijs Krijnen, an engineer at the University of Twente in the Netherlands, said that the new sensor improves on existing devices.
According to Krijnen, the artificial cupulae probably perform more efficiently than the real thing, thanks to the way the gel interacts with water.