Communications of the ACM
Mobile Gadgets That Connect to Wi-Fi Without a Battery
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A new breed of mobile wireless device does not need a battery or other energy storage to send data over Wi-Fi. A team at the University of Washington has developed prototype gadgets that obtain power by using the Wi-Fi, TV, radio, and cellular signals that are already in the air. This is accomplished by having the devices communicate without actually transmitting.
The researchers' devices send messages by scattering signals from other sources — in other words, they recycle existing radio waves instead of consuming energy to generate their own. For example, to send data to a smartphone, the prototype switches its antenna back and forth between modes that absorb and reflect the signal from a nearby Wi-Fi router. Software installed on the phone would allow it to read the signal by observing the changing strength of the signal it detects from the same router as the battery-free device soaks some of it up.
The approach could enable engineers to extend the scope of the Internet and computers into corners of the world they do not currently reach. The devices could make it easier and cheaper to widely deploy sensors in the home to control heating and other services. A paper on the devices will be presented at the ACM SIGCOMM 2014 conference in Chicago later this month.
From Technology Review
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