Camera gets energy via WiFi signals
Researchers at the University of Washington in Seattle have developed a way to transmit energy to a remote device using Wi-Fi signals. They call their way power-over-Wi-Fi or PoWi-Fi.
The research at arXiv describes how the scientists managed to build prototypes of battery-less temperature and camera sensors that derive their energy from Wi-Fi signals. The distance at which this was tested was 20 and 17 feet, respectively, or about six and five meters. They also demonstrated the possibility of wirelessly charging a nickel-metal hydride and a lithium-ion button cell battery over a distance of more than 8.5 meters. Ultimately, they tested the system in six homes to demonstrate that it is possible to successfully deliver energy over Wi-Fi without sacrificing network quality, said lead researcher Vamsi Talla at Technology Review.
In order to transmit the energy, normal Wi-Fi hotspots had to be converted, because Wi-Fi signals are normally broadcast on a single channel in a burst and not continuously. To solve this problem, the researchers programmed the routers to emit noise when a router didn’t have to send information. Adjacent Wi-Fi channels were used as carriers so that the noise did not affect data transmission.
This cannot be done by using just one router. To do this, the researchers combined the electronics from three routers, one for each channel they wanted to broadcast on. The Atheros AR9580 chipsets were programmed to transmit all three in such a way that they could transmit a constant stream of energy on a channel.
The temperature sensor continued to work at distances of up to about six meters and by adding a rechargeable battery, that distance could be increased to nine meters. The camera that was tested was an Omnivision VGA sensor that could record 174×144 pixels in black and white at 10.4 millijoules of energy per image. To store energy, a capacitor was added to the camera that activated when the capacitor was charged to 3.1V and continued to operate until the electrical voltage dropped to 2.4V. The pictures were stored on 64kB ferroelectric ram. The camera continued to work up to about five meters from the router, shooting a picture every 35 minutes.
The researchers conclude their paper that PoWiFi could be of interest to the increasing interest in internet-of-things applications where all kinds of small sensors and mobile devices are inserted into everyday objects. All these things cannot simply be connected to the electricity grid and in this way it is perhaps possible to provide some of these things with energy.