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Battery-free wireless could send text messages after your phone dies

Battery-free wireless could send text messages after your phone dies

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Whenever you send a text message, upload a photo, or check your news feed, your phone or computer directs a small amount of power to its radio, and uses that power to beam out a signal. Finding power usually isn't a huge issue, but if no direct power source were necessary at all, it would be possible to develop simple, battery-free devices that could talk to each other for purposes such as making payments, sending messages, and even monitoring the structure of buildings. Researchers from the University of Washington have put forth just such a possibility: they've proposed a new technology called "ambient backscatter" that would require no battery and could wirelessly transmit simple messages.

RFID taken to the next level

The idea may not be entirely new, but it's different in a big way. Technologies like RFID, which is often used as a simple electronic information tag, also work wirelessly and without a battery — the big difference here is that RFID requires a nearby base station be connected to a power source, whereas ambient backscatter devices would require no extra pieces at all.

That doesn't mean that the devices aren't powered though, just that they don't need a battery. But powering them up isn't something that a user would ever have to worry about: because radio waves are ubiquitously moving through the air, ambient backscatter devices would simply grab some of those radio waves and convert them into the small amount of power that they need in order to work. It can't do much with that limited power source, but it would be enough to send a signal, store information, and light up an LED.

Ambient backscatter devices would be able to require such little power because of the nontraditional method that they use for sending out radio waves. Rather than making their own signal, such devices would repurpose existing waves that are already moving through the air. By deflecting those other waves, ambient backscatter devices can alter them into their own specific communications that other devices would be able to pick up.

The limitations still aren't known

In the researchers' study, which was published at a SIGCOMM conference running this week, they note that these devices were able to work up to up to 6.5 miles away from the nearest tower broadcasting a strong wireless signal. That distance isn't necessarily the devices' upper limit, but the team didn't test them any farther away. The devices' simple structure could also limit how useful they are — but with some creative workarounds, there may be plenty of possibilities.

One example that the researchers suggest is having the devices measure how long it takes for them to receive signals from nearby transmitters. If the timing ever slowed down, it would indicate that one of the devices was moved — had they been monitoring a building, it could mean that its structure had faltered. But while the technology's most exciting application may be sending emails and text messages power-free, researchers will still need to find a battery-free way for those emails to be composed.