A battery-free camera records images and then converts the light into electric power.

A team of researchers has developed a prototype camera with a light sensor that has the properties of a solar panel. In a well lit room (300 lux) the device produces enough power to take an image per second ad infinitum.

Computer science Professor Shree K. Nayar and engineer Daniel Sims of Columbia University together with Mikhail Fridberg, head of ADSP Consulting, wrote down their findings in the paper Towards Self-Powered Cameras which will be presented at the Conference on Computational Photography in Houston.

'We are in the midst of an imaging revolution', is the opening sentence of the paper. 'Transforming fields as varied as entertainment, social networking, ecommerce, security and autonomous navigation.' And yet we are only at the beginning, according to the inventors.

'We are about to witness a second wave of the imaging revolution, one that promises to be deeper and broader in impact than the first. This wave is expected to transform diverse fields including wearable devices, internet of things, personalized medicine, smart environments, sensor networks and scientific imaging.'

In many of these emerging fields power supply is an issue. You'd basically want them to run indefinitely without having to worry about charging batteries. In the case of camera's you could fit them with solar panels but that makes them bulky. So the three devised a self-powering camera.

The image sensor in a conventional cameras consists of millions of pixels. The main component of each pixel is a photodiode, a semiconductor that converts light into a current. In the conventional pixel this property is used to measure the intensity of the light and record an image. Solar panels also work with photodiodes to convert light into electricity. In the image sensor the photodiode is in photoconductive mode while in a solar panel it is in photovoltaic mode.

Using off-the-shelf components the researchers created a 30x40 pixel array with photodiodes in photovoltaic mode. They succeeded in making the pixels switch back and forth between reading and recording images and harvesting energy to charge the sensor.

'Even though we’ve used off-the-shelf components to demonstrate our design, our sensor architecture easily lends itself to a compact solid-state imaging chip', Professor Nayar said in an interview with Columbia University. 'We believe our results are a significant step forward in developing an entirely new generation of cameras that can function for a very long duration —ideally, forever— without being externally powered.'