Battery-free devices harvest radio waves in IoT play

University of Washington researchers envision an "RF-powered Internet of Things" based upon battery-free gadgets that derive energy by harvesting ambient radio waves, such as those emanated by Wi-Fi, TV, radio and cellular.

According to the researchers, though existing technologies have been able to harvest power from ambient RF sources, they require a dedicated gateway, such as an RFID reader, for Internet connectivity. However, the researchers said their "WiFi Backscatter" system "bridges RF-powered devices with the Internet" by reusing existing Wi-Fi infrastructure to provide Internet connectivity to those devices.

The system could be used to enable, for example, in-home sensor networks. "We believe that this new capability can pave the way for the rapid deployment and adoption of RF-powered devices and achieve ubiquitous connectivity via nearby mobile devices that are Wi-Fi enabled," the researchers said.


Source: University of Washington

The group used a hardware prototype combined with commodity, off-the-shelf Wi-Fi devices to demonstrate communication rates of up to 1 kbps and ranges of up to 2.1 meters.

"You could throw these things wherever you want and never have to think about them again," Shyam Gollakota, an assistant professor at the University of Washington who worked on the project, told MIT Technology Review. Gollakota aims to set up a company to commercialize the technology, which should be applicable to other protocols such as Zigbee or Bluetooth.

Gollakota explained that harvesting ambient radio waves does not bring in lots of power, certainly not nearly enough for sending data over Wi-Fi, which demands hundreds of milliwatts minimum and more typically around one watt. So the researchers have their prototype devices communicate without actively transmitting. Instead, the devices "backscatter," or send messages by reflecting or not reflecting signals from other sources, which requires less than 10 microwatts of power.

And while the battery-free Wi-Fi devices cannot harvest enough energy to receive and decode Wi-Fi signals in the conventional way, they can detect a Wi-Fi transmission's individual packets.

The same University of Washington group demonstrated a similar initiative last year, but those early devices could only communicate with devices like themselves and did not include Wi-Fi, said MIT Technology Review. A paper on the new and improved version will be presented at the ACM Sigcomm conference in Chicago this month.

For more:
- see this University of Washington article
- see this MIT Technology Review article

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