University of Washington (UW) engineers have developed a technology that uses a Wi-Fi router—a source of ubiquitous but largely untapped energy in indoor environments—to power devices.

The engineers used the Power Over Wi-Fi (PoWiFi) system to harvest energy from Wi-Fi signals to power a temperature sensor, a low-resolution grayscale camera and a charger for a Jawbone activity tracking bracelet.

The UW team used ambient signals from this Wi-Fi router to power sensors in a low-resolution camera and other devices. Image credit: Dennis Wise/University of Washington.“We made a system that can co-exist as a Wi-Fi router and a power source," says Vamsi Talla, a UW electrical engineering doctoral student and lead author of a paper that will be presented in December at the Association for Computing Machinery’s CoNEXT 2015 conference on emerging networking experiments and technologies. "It doesn’t degrade the quality of your Wi-Fi signals while it’s powering devices.”

PoWiFi could help enable development of the Internet of Things, in which small computing sensors are embedded in everyday objects like cell phones, coffee makers, washing machines, air conditioners and mobile devices, allowing them to “talk” to each other. One challenge is how to energize those low-power sensors and actuators without needing to plug them into a power source as they become smaller and more numerous.

The team of computer science and electrical engineers found that the peak energy contained in untapped, ambient Wi-Fi signals often came close to meeting the operating requirements for some low-power devices. But because the signals are sent intermittently, energy is “leaked” out of the system during silent periods.

The team fixed that problem by optimizing a router to send out superfluous “power packets” on Wi-Fi channels not currently in use—essentially beefing up the Wi-Fi signal for power delivery—without affecting the quality and speed of data transmission. They also developed sensors that can be integrated into devices to harvest the power.

In their proof-of-concept experiments, the team demonstrated that the PoWiFi system could wirelessly power a grayscale, low-power Omnivision VGA camera from 17 feet away, allowing it to store enough energy to capture an image every 35 minutes. It also re-charged the battery of a Jawbone Up 24 wearable fitness tracker from 0% to 41% in 2.5 hours.

The researchers also tested the PoWiFi system in six homes. Users typically didn’t notice deterioration in web page loading or video streaming experiences, showing the technology could successfully deliver power via Wi-Fi in real-world conditions without degrading network performance.

Although initial experiments have harvested relatively small amounts of power, the UW team believes there is opportunity for make the PoWiFi system more efficient and robust.

“In the future, PoWi-Fi could leverage technology power scaling to further improve the efficiency of the system to enable operation at larger distances and power numerous more sensors and applications,” says Shyam Gollakota, assistant professor of computer science and engineering.