If you're living in a city, or any somewhat densely populated area, you're likely cloaked in TV and radio waves invisible to the naked eye. But what if our devices could harness this ambient energy? What if we could communicate—without needing batteries that contain toxic heavy metals—just by reflecting and remixing existing electromagnetic frequencies?
University of Washington researchers have managed to do just that. Nine months ago, electrical engineering associate professor Joshua Smith and assistant professor of computer science and engineering Shyam Gollakota started investigating how one might harvest energy from TV signals to communicate, and eventually designed two card-like devices that can swap data without using batteries. Running on what the researchers coined "ambient backscatter," the new technique is still in its infancy: Data is transferred at a rate of one kilobit per second and requires a distance no greater than 2.5 feet apart. Still, it has exciting implications, they say, for the "Internet of things."
"I think the Internet of things looks like many objects that kind of have an identity and state—they can talk to each other. Ultimately, I think people want to view this information," Smith says. On the device's website, the team provides a couple of examples of applications they envision. What if, for instance, you leave your keys on the couch, but both the keys and the couch have embedded backscatter devices? One day, maybe your couch could text your phone after it detects your keys, telling you you're an idiot for leaving them on the couch. Smith also cites sensors embedded in roofs that can alert people when there's a water leak, or backscatter devices build into bridges to notify safety crews when there's a structural danger, such as a crack.
"That’s part of the vision. There will be information about objects in the physical world that we can access," Smith says.
The device works by capturing existing energy and reflecting it, like a transistor, Gollakota explains. "Every object around you is reflecting signals. Imagine you have a desk that is wooden, and it's reflecting signals, but if you actually make [the desk] iron, it’s going to reflect a much larger amount of energy. We’re trying to replicate that on an analog device."
Gollakota adds that our current communications and computing devices require a lot of power, even by battery, in order to function—like a FitBit wristband or Google Glass. "So by using a technique like ambient backscatter they can consume less power," he says.
As for the device's current limitations, Smith points out that most places out of range of TV towers will probably be within range in the coming years, as energy efficiency improves. The energy harvester they used for the paper, which they presented at the Association for Computing Machinery's Special Interest Group on Data Communication in Hong Kong, requires 100 microwatts to turn on, but the team says it has a design that can run on as low as 15 microwatts. Meanwhile, the technique is already capable of communicating location, identity, and sensor data.
The University of Washington presentation took home "best paper" in Hong Kong, and researchers say they're excited to start exploring commercial applications. "We've had emails from different places—sewer systems, people who have been constrained by the fact that you need to recharge things," Gollakota says. "Our goal for next six months is to increase the data rate it can achieve."