Thanks to New Scientist for this:

Sharp metal propellers can harm wildlife, so an alternative made using ferrofluid could be a better approach, if it can be tweaked to work at higher speeds

A robot boat with a propeller made from liquid magnets could be a safer alternative than solid metal blades, which can damage wildlife.

Jun Shintake at the University of Electro-Communications in Chōfu, Japan, and his colleagues created a prototype aquatic craft with a propeller made from ferrofluid, which consists of magnetic iron oxide nanoparticles suspended in oil. It is controlled with electromagnets that switch on and off at high speed.

“One day, I was thinking about oil and water and how they do not mix with each other, which means there should be some kind of reaction force between the two,” says Shintake. “Based on this fact, we decided to make a robot using this interaction between a fluid and a fluid.”

Shintake and his team attached two blobs of ferrofluid to opposite sides of a square acrylic plate that extended into water, with a platform to house a battery and electronics for electromagnets above. They found that when they triggered the ferrofluid to shift from side to side, at a rate of about nine times per second, the craft moved forward at around 2.7 millimetres per second. The researchers could also rotate the craft clockwise and counterclockwise by alternating the pattern of ferrofluid shifting.

The softer nature of fluid-fluid interactions should reduce damage to wildlife if deployed in a real-life craft, says Shintake.

Li Zhang at the Chinese University of Hong Kong points out that the propeller is currently too slow to be useful, but this could be improved by having several ferrofluid propellers working at once.

Scientific Paper

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