PoWi-Fi for powering the next Billion Devices with Wi-Fi
Starting in the late 19th century, Nikola Tesla dreamed of eliminating wires for both power and communication.
As of the early 21st century, wireless communication is extremely well established, billions of people rely on it every day. Wireless power however has not been as successful.
In recent years, near-field, short range schemes are gaining traction for certain range-limited applications, like powering implanted medical devices and recharging cars and
phones from power delivery mats. More recently researchers have demonstrated the feasibility of powering sensors and devices in the far field using RF signals from TV and cellular base stations. This is exciting, because in addition to enabling power delivery at farther distances, RF signals can be used to simultaneously charge multiple devices due to their broadcast nature.
Now researchers at University of Washington have developed a new approach called “power over Wi-Fi or PoWi-Fi” for drawing enough power from standard Wi-Fi signals to power a security camera and recharge a fitness tracker. The team behind this project believes its techniques will be useful for powering the many devices expected to form the “internet of things”.
Wi-Fi router, can provide far field wireless power without compromising the network’s communication performance.
The researchers had built prototype of battery-free temperature and camera sensors that are powered using Wi-Fi chipsets with ranges of more than 17 feet.
They also demonstrated the ability to wirelessly recharge nickel–metal hydride and lithium-ion coin-cell batteries at distances of up to 28 feet
And, they deployed their system in six homes in a metropolitan area and showed that it can successfully deliver power via Wi-Fi in real-world network conditions.
The idea is simple in concept. Wi-Fi radio broadcasts are a form of energy that a simple antenna can pick up. Until now, Wi-Fi receivers have all been designed to harvest the information that these broadcasts carry.
But researchers point out that there is no reason why the energy shouldn’t be harvested as well. The question is how much can be gathered in this way. And therein lies the challenge.
The University of Washington team’s approach to this is refreshingly straightforward. They simply connect an antenna to a temperature sensor, place it close to a Wi-Fi router and measure the resulting voltages in the device and for how long it can operate on this remote power source alone.
The simple answer is that the voltage across the sensor is never high enough to cross the operating threshold of around 300 millivolts. However, it often comes close.
But a closer examination of the data makes for interesting reading. The problem is that Wi-Fi broadcasts are not continuous. Routers tend to broadcast on a single channel in bursts. This provides enough power for the sensor but as soon as the broadcast stops, the voltages drop. The result is that, on average, the sensor does not have enough juice to work.
That gave the researchers an idea. Why not program the router to broadcast noise when it is not broadcasting information and employ adjacent Wi-Fi channels to carry it so that it doesn’t interfere with data rates.
And that’s exactly what they’ve done. They modified standard wi-fi hotspots and routers to broadcast noise when a channel was not being used to send data. This meant the power of the wi-fi signals stayed constant and, though low, was high enough to power some components.
The ability to deliver power wirelessly to a wide range of autonomous devices and sensors is hugely significant. But the real icing on the cake here is the ability to do this with ordinary technology that is commonly available all over the developed world and beyond. As such, PoWi-Fi could be the enabling technology that finally brings the Internet of things to life.
Source: http://www.technologyreview.com/view/...