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 The prototype self-powering camera takes an image each second, and
in a well-lit scene it can operate indefinitely.
The team is led by Shree Nayar, Professor of Computer Science at
Columbia Engineering,
"What we have designed here is an image sensor with pixels, with
this new design that can not only capture pictures but also generate
power from the pixels, in order to capture the images themselves.
And that leads us to a fully powered image sensor," Nayar explained
to Reuters on Thursday (April 16).
An image sensor is a sensor inside every camera that is responsible
for capturing the image. It does so by converting the light
information it receives into signals that convey the image. In
modern cameras photo diodes, tiny devices inside each pixels of the
image sensor, measure the amount of light that falls onto it, and
Nayar said he noticed that the process is similar to photo diodes
used inside solar panels to harvest energy.
"It turns out exactly the photo diode is also used in solar cells
which are used in solar panels to harvest energy from light, except
that they are being used in a slightly different circuit. So our
thinking was to create, redesign the pixel in the camera so that it
can serve both purposes."
In order to build the prototype Nayar worked with research engineer
Daniel Sims, and used off-the-shelf components to fabricate an image
sensor with 30x40 pixels - the lowest resolution needed for a human
face to be recognized.
The pixel design is very simple, and uses two transistors.
The image sensor continuously toggles between image capture and
power harvesting modes, and during each image capture cycle, the
pixels are used first to record and read out the image and then to
harvest energy and charge the sensor's power supply.
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A well-lit indoor scene of around 300 lux delivers enough power for
the camera to operate indefinitely. Daylight in a typical overcast
day measures several thousand lux.
While the prototype self-powering camera is large in size, Nayar
says that it can be shrunk down to fit on a small chip.
"What we have done is a calculation that shows that you can take the
same design and make a compact image sensor chip with it. Of course
that chip would be able to capture less light and therefore harvest
less energy, because it is smaller. But it turns out when you make
it a chip it also consumes less power," he said.
The prototype cost several thousands of dollars to build, but on an
industrial scale Nayar believes the production cost of his image
sensor will be similar to a conventional chip found in cell phones
and computers.
A more compact size would also allow for many different
implementations, such as in security cameras and consumer
electronics.
Ultimately Nayar hopes that in the future his image sensor can be
further improved so that it can also function as a power source when
not capturing images.
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