Thursday, 21 August 2014
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CMOS camera provides 3D picture of surroundings

Researchers at Nottingham University are developing a 3D camera they hope could become part of Europe’s first Mars rover.

The team has submitted proposals to the European Space Agency (ESA) detailing its work on a time-of-flight camera that could help a rover plan its route by providing depth information on its surroundings.

These cameras work by firing light at their targets and use the reflected beams to calculate how far away objects are and build up a 3D picture of the target area.

The Nottingham team is working to make the complementary metal-oxide-semiconductor (CMOS) camera operate across a range of different distances and resolutions rather than at fixed points.

This will make it easier and more flexible to use, opening it up to a range of potential applications including sensors for spacecraft docking and a collision-detection system for cars.

‘Other cameras like this exist in a few other forms but they all suffer from the same problem - that it is difficult to get enough light back,’ said Samuel Achamfuo-Yeboah, the Nottingham PhD student developing the camera.

Achamfuo-Yeboah has been able to increase the amount of light captured in each pixel of the image by simplifying the circuitry.

‘For each pixel there is something called a fill factor – that’s the percentage of the pixel that actually receives light,’ he said.

‘Before, it was about nine per cent because the other parts that do the signal processing take up the rest of the circuitry.

‘What I’ve done is reduce the complexity of the other circuits, which means there’s more room to receive light. So now I’ve pushed it up to 16 per cent.

Time-of-flight cameras send out a modulated beam, meaning the wave amplitude changes in a regular pattern. A device called a mixer compares the reflected light against a local reference beam to measure how the wave angle (phase) has shifted.

This can be used to calculate how far the light has travelled. The greater the wavelength of the modulation pattern (and the lower the frequency), the further the beam can travel before being measured.

Achamfuo-Yeboah hopes to develop the camera to operate between 100kHz and 50MHz, meaning it could potentially detect objects within a range of 1,500m and 3m.

At the greater distances, the resolution would be too weak to produce useful images but the technology could be used as a docking sensor for spacecraft.

Achamfuo-Yeboah also hopes that the rover camera could operate successfully at a lowest frequency of 1MHz, meaning it could see objects over a distance of up to 150m.

 


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