Just yesterday I reported on the impossibility to use energy scavenging unless you are contented with a low power feed. If you want to send signals using WiFi you need quite a few mW of power and this is above energy scavenging possibility (of today at least).
Yet, it would be good to have battery-less sensors in our homes communicating using the WiFi network that is now a common presence there.
IF something is impossible, thought researchers at the University of Washington, you've got to find a different way for doing it. And they did.
This team is the same one that have developed an antenna to harvest ambient energy for IoT powering and I remember posting the news last year in August. Now they have developed a better energy scavenging antenna (see in the picture) but still the power output is not sufficient to let IoT communicate using the home WiFI.
They have come up with a solution, in the stile of Francis Bacon observation: "If the hill will not come to Mahomet, Mahomet will go to the hill". Which translate: "let's find a different way to communicate via wifi that is cheaper in terms of energy".
What they did was to use backscattering technique: rather than having the IoT device using wifi to send messages one use the wifi to harvest energy (a tiny bit) and use that energy to disrupt the wifi signal, like creating interference. This requires much less power, in the order of µW, rather than mW, a thousand times less.
The receiver in the wifi gateway can detect these disturbances and can work out their meaning, i.e. extract the information the IoT wants to send. Et le voilà! You can watch the clip to get the details in a graphic way.
This approach requires a modification in the WiFI receiver but that should not be a costly one, given the number of wifi kits being produced and should enable battery-less IoT sensors to be disseminated in the home, in department stores,... every where there is a wifi hot spot, and there are millions of them. Not having a battery in an IoT device significantly cuts the cost thus increasing its market space.
Interesting how researchers don't stop when confronted with the "impossible". They just look for an alternative approach.