Ghost in the machine –

Ghost in the machine Published:  20 February, 2014

Erik Sviland/MacIver

INNOVATIVE research into underwater robotics is drawing inspiration from electric fish from South America.

Scientists at Northwestern University in Illinois have been closely studying ghost knifefish, which sense their environment with a small electric current and move with the help of a long, undulating fin.

Scientists are confident that both of these adaptations can be utilised to produce effective underwater vehicles, devices which have proved elusive thus far, as explained by Professor Malcolm MacIver:

‘Today, we don’t really have underwater robots that work well in really cluttered conditions or in conditions where vision isn’t useful. Just consider the sunken cruise ship. It is very dangerous to send divers into such situations where the water can be very cloudy.

‘But we can learn from the electric fish. They don’t use vision to hunt at night in the rivers of the Amazon basin, and their movement through the cluttered root masses and flooded forests requires incredible precision. They fill a big hole in terms of our capabilities in underwater robots.’

Professor MacIver has spent a number of years studying the knifefish, which hunt in total darkness by generating an electric field from neurons along their spinal cord. This field is disturbed when the fish comes into contact with its prey.


‘The fish have evolved an amazing system,’ said MacIver. ‘Imagine your retina stretched over your entire body and what that would be like. That’s the situation that knifefish find themselves in.

‘They perceive in all directions. They emit a kind of radar, but it’s an electric field; and the sensory receptors scattered over their entire body surface mean they can detect things coming from all directions.’

The Northwestern scientists have developed a number of prototypes based on the knifefish and have successfully enabled a robot in a tank to react to its surroundings and change direction accordingly.

The technology in Prof MacIver’s lab is now simulating this enabling a robot in a tank to react to what is around it and move accordingly. The next stage in the robot’s development is to simulate the knifefish’s undulating fin:

‘From all our simulations, we now have mathematical relationships between things like the frequency and amplitude of the travelling wave and how much propulsion you get,’ explained Prof MacIver. ‘So now we can put that into technology and get it to work properly.’


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