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Oct 16, 2015 | By Benedict

Just how do those harbor seals do it? Engineers at MIT have been conducting research into the prey-sensing ability of harbor seals by creating a large-scale, 3D printed replica of one of their whiskers. Experiments conducted with the artificial whisker have confirmed scientific suspicions about whiskers playing a key role in sensing prey.

It has long been observed that harbor seals are extremely efficient predators. Their sense for detecting prey is highly attuned and highly unique, with the creatures being able to sense the path of a swimming object up to 30 seconds after its passing, even while blindfolded. This extremely precise tracking ability was presumed to be down to the seals’ whiskers, which appear to function like antenna.

A team of researches at MIT, led by Heather Beem, PhD graduate, and Michael Triantafyllou, William I. Koch Professor in MIT’s Department of Mechanical Engineering, have been working on a project which aims to uncover the science behind the whiskers of the harbor seal. By creating a large, 3D printed whisker-like device, they were able to conduct experiments in a 30-meter-long tank of water to discover how the whiskers function.

Harbor seal whiskers have a unique, wavy shape. They have an elliptical cross-section, only visible under a microscope, which varies in size along its span. “It’s marvelous to see this intricate pattern, it’s not just a straight antenna—it’s a perfect sinusoid,” said Prof. Triantafyllou.

The results of the experiments are intriguing. The researchers saw that, when the 3D printed whisker entered the wake of a passing object, it vibrated at the same frequency as the wake’s passing vortices—the “whirlpools” left behind by the object, playing the role of prey. Visualisations of collected data showed the whisker to “slalom” in and out among the vortices.

The scientists were able to prove that this slaloming motion actually allowed the whisker to extract energy from the wake of the pursued object, causing the replicated vibrations in the whisker. The ability of the whisker to replicate the vibrations of the object’s wake thus appears to inform the seal about the object’s path, size, and shape—letting it know whether the prey should be pursued or not!

Unlike long, straight rods, the seals’ wavy whiskers create relatively weak vortices, which offers a big advantage when hunting. The researchers believe that the unique whisker shape helps the seal to minimise sound from its own movement. “It’s like having the ability to stick your head out of a car window, and have there be no noise, so that your ears don’t ring: It’s a quieting effect,” Prof. Triantafyllou explained.

“The geometry of the whisker allows for this phenomenon of being able to move very silently through the water if the water’s calm, and extract energy from the fish’s wake in order to vibrate a lot,” added Beem. “Now we have an idea of how it’s possible that seals can find fish that they can’t see.”

Prof. Triantafyllou believes that their findings, and the production of similar biologically inspired sensors, 3D printed or otherwise, could aid scientists in tracking both schools of fish and sources of pollution. “We already have a few sensors that can detect velocity, but now that we know better what they can do, we can use them to track sources of pollution and the like. By having several whiskers on a vehicle, like the seal, you can, for example, detect a faraway plume, and track it all the way to the end.”

MIT’s whisker research was partially supported by the Office of Naval Research, the Singapore-MIT Alliance for Research and Technology, and the MIT Sea Grant program.

 

 

Posted in 3D Printing Application

 

 

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