Engineers at University of Michigan have recently come up with just that, an image sensor that does both things well enough to capture 15 images per second powered only by the daylight falling on it.
Engineers have previously investigated the possibility of having a camera sensor power itself with the same light that falls on it. After all, it’s basically just two different functions of a photovoltaic cell — one stores the energy that falls on it while the other records how much energy fell on it.
The problem is that if you have a cell doing one thing, it can’t do the other. So if you want to have a sensor of a certain size, you have to dedicate a certain amount of that real estate to collecting power, or else swap the cells rapidly between performing the two tasks
The prototype sensor they built is less than a square millimeter, and fully self-powered in sunlight. It captured images at up to 15 frames per second of pretty reasonable quality.
Though the prototype imager was constructed using standard CMOS process technology, its pixels require both a different structure and different electrical characteristics from those on a standard imager. Most obviously, the new pixel contains a p-n junction, an extra diode essentially, beneath the image sensing diode.
In the paper, the researchers point out that they could easily produce better images with a few tweaks to the sensor, and Park tells IEEE Spectrum that the power consumption of the chip is also not optimized — so it could also operate at higher framerates or lower lighting levels.
Ultimately the sensor could be essentially a nearly invisible camera that operates forever with no need for a battery or even wireless power.