Imagine these formerly dumb systems gone smart: a roof that announces when it’s about to spring a leak; a garden that monitors moisture on its own and applies just the right amount of water when it’s needed; and a bridge that automatically puts in a work order at the first sign of a hairline crack in a support structure.
These are just a few of the innovations promised by the growth of the industrial internet, a communications network in which objects and machines generate data about themselves and communicate it with each other to make better decisions about how they operate. This advance promises major efficiency gains—think of a jet engine monitoring and injecting fuel precisely when it’s needed. It will also mean cost reductions through repair and maintenance that head off problems before they become major, among other advantages. But for this more-automatic world to take root, objects of all sorts need to be embedded with simple instruments—moisture detectors, accelerometers, and identification chips—that can sense and communicate their state to the broader world.
One of the major constraints of this potentially disruptive technology taking off is the power requirement of these sensors, which must be fed either by wires or batteries. But how does one install a wireless moisture detector into a roof and then periodically go in to change the batteries? How would a farmer gather up thousands of cheap sensors embedded in the soil that tell an irrigation system when to work after they’ve been spread over the land?
“Sensors have needed batteries up until now, which makes deploying them difficult because you have to maintain those batteries,” University of Washington computer science and engineering professor Shyam Gollakota tells Txchnologist. “We asked, ‘Can you generate power without batteries?’”
Based on a project Gollakota’s team has been pursuing over the last few years, the answer may just be yes. They have developed a wireless communication system that lets sensors transmit and receive data, all while pulling power from TV broadcast waves in the environment around them. The device uses ambient signals as both a power source and a communications medium.
“There are signals all around us—TV, radio, cellular phones,” says Joshua Smith, a UW associate professor of computer science and engineering and of electrical engineering, who is working with Gollakota on the project. “Our sensor continuously harvests this energy for power and either reflects these signals or absorbs them to communicate, which changes what a second device sees.”
Found power, bounced signals
They have tuned their small, battery-free sensors to harvest the electromagnetic radiation constantly pumped out of television transmitters, which push their signals in all directions with one megawatt of power. They are now working to let the devices use cellular phone transmissions, as well. “We’ve been surrounded by all this energy that’s out there for a while now,” says Smith. “We just didn’t think of it as power, but only as information signals.”
The devices operate using something called ambient backscatter, which lets two or more sensors communicate using already present broadcast transmissions instead of generating their own radio waves. They say this method is “orders of magnitude more power-efficient than traditional radio communication.”
Very generally, their devices communicate by either reflecting or absorbing television signals—a reflection representing a ‘1’ and an absorption meaning a ‘0’. Each device also sends a header of 16 bits of identifying data so that the receiving sensor can validate from where the signal is coming.
The UW team’s sensors can harvest on the order of 100 microwatts of energy from ambient broadcast signals, and they consume around .5 microwatts to reflect signals in order to communicate. Gollakota says they can get the effective communication range between sensors up to 20 feet, though their prototype operates at a maximum of about 2.5 feet.
Many possible uses
Smith says they’ve already successfully produced a number of batter-free sensors—which use ceramic capacitors to store the energy they harvest—including ones that can detect gases, movement or moisture. The latter, he says, could be embedded directly within roof tiles to monitor for leaks. “For the right application, our ambient backscatter sensors could be commercialized really fast, like within a year or two,” he says.
Their innovation is different from that which is used in radio frequency identification—the technology now commonly employed to track objects, to pay for goods using smartphones and as a security measure in modern passports. RFID requires a powered reader to provide it energy. “Ours is like an RFID without the need for a powered reader,” Gollakota says.
Beyond their possible use as the instruments of the industrial internet, Gollakota also sees the sensors as becoming ubiquitous in the average person’s life. “These sensors could be used as cheap tags for anything—keys, wallets—so that you never lose them again, or as part of personal devices like health monitors that are made much smaller because they don’t need batteries,” he says. “We are getting rid of the batteries.”