Power over Wi-Fi: How does it work?

Alan Martin June 9, 2015

Big cities can house hundreds of thousands of Wi-Fi points, not all of which are transmitting data all the time. What if they could be put to for something other than Netflix streaming and Reddit consumption?

This is the premise of a scientific paper from the University of Washington with the attention-grabbing title “Powering the Next Billion Devices over Wi-Fi”.

Ignore the next billion devices for a second – what are the first? Well, the researchers discovered that they could supply power to a basic camera 17ft from a router, and managed to boost a fitness tracker’s battery to 41% in two-and-a-half hours.

How does it work?

Wi-Fi routers can already transmit power. PoWiFi works by forcing routers to send out a constant 1W signal, rather than the intermittent kind used currently, which is then captured and turned into DC power by harvesters.

In an interview with Popular Science, Vamsi Talla, a PhD candidate at the university and one of the paper’s co-authors, said: “We have a huge Wi-Fi infrastructure already in place. If we can repurpose existing infrastructure for power delivery as well, then we can actually enable wireless power delivery in homes and offices.”

Won’t that harm Wi-Fi signal?

It should, but the average layman might not notice. As part of the trial, the researchers equipped six Seattle homes with PoWiFi; of these, four noticed no difference, while one found their internet speed actually improved – although the researchers note that the PoWiFi was actually an upgrade from their previous model.

Is it time to throw away your chargers?

Hold your horses – and not with your device cables, which you should absolutely not throw out. The technology is promising, but it’s evidently not right for charging your smartphone, your tablet, your laptop or other power-hungry devices.

Remember how we said it powered a camera? This is the camera in question:

wifi_camera

What’s more, the charge from the PoWiFi only powered it sufficiently to take one 177 x 144 black-and-white photo every 35 minutes. That’s not going to keep Instagram in the photographic lifestyle to which it has grown accustomed.

Part of this is down to FCC regulations, which limit routers to 1W output (iPhone and Android chargers typically output at 5W). However, even if the restrictions were lifted, powering devices this way wouldn’t be lightning fast. What’s more, it would be far more wasteful than using a wired charger, not to mention the fact that FCC regulations – cautious or not – are there for a reason.

There is certainly potential for smaller devices, though, and things are only at the proof-of-concept stage – just don’t expect your phone to be charged using Wi-Fi. To put things into perspective, Computer World calculates that the electricity generated this way is 100,000 times too low even to run a smartphone, without giving a thought to charging.

In short, you’re stuck with wires for the foreseeable future.

Image: Quintanomedia under Creative Commons