Sensors Use Building's Electrical Wiring as Antenna

Wireless sensors scattered throughout a building can monitor everything from humidity and temperature to air quality and light levels. This seems like a good idea--until you consider the hassle and cost of replacing the sensors' batteries every couple of years. The problem is that most wireless sensors transmit data in a way that drains battery power.
Researchers at the University of Washington have come up with a way to reduce the amount of power a sensor uses to transmit data by leveraging the electrical wiring in a building's walls as an antenna that propagates the signal. The approach extends a wireless sensor's range, and it means that its battery can last up to five times longer than existing sensors, say the researchers.

The technology, called Sensor Nodes Utilizing Powerline Infrastructure (SNUPI), sends a small trickle of data wirelessly at a frequency that resonates with the copper wiring in a building's walls, says Shwetak Patel, professor of computer science and electrical engineering at the University of Washington. The copper wiring, which can be up to 15 feet away from the sensors, picks up the signal and acts as a giant receiving antenna, transmitting the data at 27 megahertz to a base station plugged into an electrical outlet somewhere in the building.

"The powerline has an amplification effect," says Patel. While many low-power sensors only have a range of a few feet, he says, his prototype sensors can cover most of a 3,000-square-foot home. In most wireless sensor schemes, Patel says, walls impede transmission of sensor data, but with SNUPI, "the more walls in the home, the better our system works." A paper describing the work will be presented at the Ubiquitous Computing conference in Copenhagen, Denmark, in September.