Imagine a home that could tell the owner when water is dripping into an attic crawl space or if an open window is letting hot air escape during winter. It may be possible thanks to a device that uses a home’s electrical wiring as a giant antenna.
Researchers at the University of Washington (UW) and the Georgia Institute of Technology have developed sensors that use residential wiring to transmit information to and from almost anywhere in the home, allowing for wireless sensors that run for decades on a single watch battery. Low-cost sensors recording a building’s temperature, humidity, lighting level or air quality are central to the concept of a smart, energy-efficient home that automatically adapts to its surroundings. But that concept has yet to become a reality.
“When you look at home sensing, and home automation in general, it hasn’t really taken off,” said Shwetak Patel, principal investigator and a UW assistant professor of computer science and electrical engineering. “Existing technology is still power-hungry and not as easy to deploy as you would want it to be.”
That’s largely because today’s wireless devices either transmit a signal only several feet or consume so much energy they need frequent battery replacements, Patel said.
“Here, we can imagine this having an out-of-the-box experience where the device already has a battery in it, and it’s ready to go and run for many years,” Patel said.
Users could easily sprinkle dozens of sensors throughout the home, even behind walls or in hard-to-reach places such as attics or crawl spaces.
Patel’s team has devised a way to use copper electrical wiring as an antenna to receive wireless signals at a set frequency. A low-power sensor placed within 15 feet of electrical wiring can use the antenna to send data to a single base station plugged in anywhere in the home.
The device is called sensor nodes utilizing powerline infrastructure (SNUPI). It originated when Patel and co-author Erich Stuntebeck were doctoral students at Georgia Tech and worked with thesis adviser Gregory Abowd to develop a method using electrical wiring to receive wireless signals in a home. They discovered that home wiring is a remarkably efficient antenna at 27 megahertz. Since then, Patel’s team at UW has built the actual sensors and refined this method. Other co-authors are UW’s Gabe Cohn, Jagdish Pandey and Brian Otis.
Cohn, a UW doctoral student in electrical engineering, was lead student researcher and tested the system. In a 3,000-square-foot house, he tried five locations in each room and found that only 5 percent of the house was out of the system’s range, compared to 23 percent when using over-the-air communication at the same power level. Cohn also discovered some surprising twists: that the sensors can transmit near bathtubs because the electrical grounding wire is typically tied to the copper plumbing pipes, that a lamp cord plugged into an outlet acts as part of the antenna, and that outdoor wiring can extend the sensors’ range outside the home.
While traditional wireless systems have trouble sending signals through walls, this system actually does better around walls that contain electrical wiring.
Most significantly, SNUPI uses less than 1 percent of the power for data transmission.
The researchers are commercializing the base technology, believing it could be used as a sensing-system platform.