House acts as its own antenna
A sensor that uses a home's electrical wiring as a giant antenna has the potential to run for decades on a single watch battery. (Credit: Gabe Cohn)
U. WASHINGTON (US)— Scientists have developed a device that uses a home's electrical wiring as a giant antenna.
The sensors use the 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, light 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," says Shwetak Patel, assistant professor of computer science and of electrical engineering at the University of Washington.
"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, Patel says, or consume so much energy they need frequent battery replacements.
Patel's team has devised a way to use copper electrical wiring as a giant antenna to receive wireless signals at a set frequency.
A low-power sensor placed within 10 to 15 feet of electrical wiring can use the antenna to send data to a single base station plugged in anywhere in the home.
The Sensor Nodes Utilizing Powerline Infrastructure device originated when Patel and co-author Erich Stuntebeck were doctoral students at Georgia Tech and discovered that home wiring is an efficient antenna. Since then, Patel's team has built the actual sensors and refined this method.
Gabe Cohn, a UW doctoral student 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.
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 compared to the next most efficient model.
The existing prototype uses UW-built custom electronics and consumes less than 1 milliwatt of power when transmitting, with less than 10 percent of that devoted to communication.
Depending on the attached sensor, the device could run continuously for 50 years, much longer than the decade-long shelf life of its battery.
Longer-term applications might consider using more costly medical-grade batteries, which have a longer shelf life.
The team is also looking to reduce the power consumption even further so no battery would be needed. They say they're already near the point where solar energy or body motion could provide enough energy.
The researchers are commercializing the base technology, which they believe could be used as a platform for a variety of sensing systems.
Another potential application is in health care. Medical monitoring needs a compact device that can sense pulse, blood pressure or other properties and beam the information back to a central database, without requiring patients to replace the batteries.
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