Mobile Wi-Fi Gizmos Don’t Need No Stinkin’ Batteries

Forget the better mousetrap. Research today seems focused on making a better battery – smaller but with greater capacity, lighter, and quick to recharge. That's the key to truly portable, useful electronic devices.

Unless, of course, the battery becomes unnecessary altogether.

The key to most portable devices is the ability to send and receive signals, whether to make or accept cell phone calls, to receive television and radio signals, and to communicate with the Internet via Wi-Fi. Now researchers at the University of Washington say they can provide power too, cutting batteries from the equation.

The possibilities of such technology are virtually endless. For example, devices that can communicate without relying on electrical connections – whether from a wall socket or even a battery – could dramatically reduce the cost of and increase the ease of installing sensors in homes that control their maintenance remotely, whether to fix a refrigerator that's acting up or adjust central heating.

Their new technology, called Wi-Fi Backscatter, could be what will make the Internet of Things a reality.

Take home thermostats. Stick one on the wall of a home's living room and it can monitor the heat there, but only there, unless the builder had the foresight and the money to wire the entire home to place a temperature sensor in every room to ensure even heat or cooling.

Now, though, a homeowner can install inexpensive battery-free devices with Wi-Fi capability virtually anywhere to provide the furnace or air conditioner with the information to maintain a constant temperature everywhere.

"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 the MIT Technology Review.

In 2013, the same group of researchers demonstrated a similar design, although without Wi-Fi, but the devices could communicate only with other devices equipped with the same technology. But with added Wi-Fi connectivity, the devices can link up with any other unit through Wi-Fi signals.

Researchers have tried to collect power from radio signals for years. There's enough energy available to run low-power circuits, Gollakota said, but not enough to transmit signals. So his team devised a way to have their devices communicate without out actively transmitting. Instead, he said, they send messages by recycling ambient radio waves rather than generating their own.

Here's how to make a smart phone call based on Wi-Fi Backscatter technology: The device toggles its antenna between modes that alternately absorb and reflect a signal from an accessible Wi-Fi router. The absorption cycle powers the phone from the Wi-Fi signal, while the reflective mode uses that power to send its own signal.

The team plans to present its findings at the ACM Sigcomm conference in Chicago on Aug. 17-22.