The video is simple enough. A man changes facial expressions before moving his head up and down then side-to-side in a clip that looks a bit like a moving daguerreotype captured more than a century and a half ago. The camera used to capture this head shot is cutting edge, however, using a new light-powered technology, which could lead to battery-free cameras that never shut down.
That concept includes combining a camera image sensor’s ability to collect and measure light with a photovoltaic cell’s capacity to convert some of that light into energy. The result, at least at this stage, is a crude yet self-sufficient digital camera developed at Columbia University. During each image capture cycle the pixels in the sensor first record and produce an image then harvest energy and charge the sensor’s power supply.
As cameras become critical parts of networks, wearable gadgets and other components of the so-called Internet of Things, “you want a device that is really small, high quality and can capture images untethered—and can to do it forever,” says Columbia computer science professor Shree Nayar, who created the self-powered camera with his colleague, research engineer Daniel Sims, along with Mikhail Fridberg, who heads ADSP Consulting in Sharon, Mass. Nayar is presenting his team’s research, which was funded by the U.S. Office of Naval Research, next week at the IEEE International Conference on Computational Photography at Rice University in Houston.
The handful of self-powered cameras currently on the market are generally powered by solar cells. Nayar’s prototype camera does not need a battery but instead uses a supercapacitor that is continuously charged by energy harvested from the image sensor’s pixels. The current iteration of the camera can capture black-and-white 30-by-40-pixel images each second over an indefinite period of time for a scene that is about 300 lux in brightness. That may be low resolution but it proves the concept’s feasibility, says Nayar, who is also director of the Columbia School of Engineering’s Computer Vision Laboratory.
The camera could be installed as a surveillance device and function even during prolonged periods of darkness by storing and using excess power harvested in the daytime to generate images at night. A sunlight scene is several thousands of lux in brightness, far more than the 300 lux required to make the camera self-powered, Nayar says.
A compact camera equipped with a solid-state version of the self-powered image sensor would be able to produce at least a 200-by-200-pixel image per second, Nayar adds. With continued improvements in resolution such a camera could prove useful in smartphones and wearable devices, given their poor battery life, and might eventually even be used to recharge the battery when not taking video.