A compass that relies on polarised light can use the sun to tell where magnetic north is, even when it is cloudy. It is based on how some insects navigate and could be used when conventional magnetic compasses aren鈥檛 reliable, such as on robotic drones.
Insects like ants and bees can sense direction using sunlight鈥檚 intensity and its polarisation, a measure of how light rays can appear twisted, through specially adapted receptors arranged in a ring in their eyes.
This lets them deduce and track the sun鈥檚 position and use it as a reference point, like a magnetic compass pointing to the north pole. It works even on a cloudy day, because polarisation can still be detected in these conditions.
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at the University of Edinburgh, UK, and his colleagues have built a compass from eight light receptors arranged in a ring that mimics how insects鈥� eyes measure polarised light.
Daylight is most polarised at 90 degrees from an observer鈥檚 line-of-sight to the sun, so by measuring this polarisation and the brightness of the light, Gkanias and his colleagues could use a simple computer algorithm to accurately find the sun鈥檚 position.
The researchers tested the compass on a wheeled robot in Italy and South Africa, in the same kind of habitats as desert ants and dung beetles have. They found it could track the sun鈥檚 position relatively accurately, but because of problems lining up the robot with magnetic north at the beginning, the sensor was less accurate than they had predicted. Correcting for this error would have made it better than other compasses that detect polarised light, says Gkanias.
The compass could be useful when magnetic compasses don鈥檛 work, such as on drones, which have rotors that generate interfering magnetic fields of their own. However, the device is about 15 centimetres across, so would first need to be made smaller, says Gkanias.
It could also be useful in better understanding how insects navigate, says at the Institute for Bird Research in Wilhelmshaven, Germany. 鈥淭his allows us to test the plausibility of any mechanistic hypothesis in animals, because in these technical systems we can manipulate single components or mechanisms,鈥� she says.
Although the compass is designed for working during the day, Gkanias says they got some data at dawn showing that moonlight could interfere with the detection of light from the sun. This means it might also work at night if they built in a function to add the tracking of the movement of the moon or the Milky Way.
Nature Communications
