Researchers in America say they have created a wireless communication system that allows devices to communicate with each other without relying on batteries or wires for power and could play a vital role in the Internet of Things.
The communication technique - dubbed "ambient backscatter" by the University of Washington scientists - allows devices to communicate with each other by reflecting or absorbing pre-existing radio signals from TV and mobile transmissions.
The energy-saving breakthrough could be particularly well suited to a home-based Internet of Things scenario where devices are usually within a few meters of each other.
The team has built small, battery-free devices with antennas that can detect, harness and reflect a TV signal, which is then picked up by other similar devices.
"We can repurpose wireless signals that are already around us into both a source of power and a communication medium," said lead researcher Shyam Gollakota, a University of Washington assistant professor of computer science and engineering.
"It's hopefully going to have applications in a number of areas including wearable computing, smart homes and self-sustaining sensor networks."
The researchers published their results at the Association for Computing Machinery's Special Interest Group on Data Communication 2013 conference in Hong Kong, taking place in Hong Kong this week. They have received the conference's best-paper award for their research.
"Our devices form a network out of thin air," said co-author Joshua Smith, a UW associate professor of computer science and engineering. "You can reflect these signals slightly to create a Morse code of communication between battery-free devices."
According to the university, smart sensors could be built and placed permanently inside nearly any structure, then set to communicate with each other. It is claimed that the sensors could be placed in a bridge to monitor the health of the concrete and steel, then send an alert if one of the sensors picks up a hairline crack. The technology can also be used for communication - text messages and emails, for example - in wearable devices.
The researchers tested the ambient backscatter technique with credit card-sized prototype devices placed within several feet of each other. For each device the researchers built antennas into ordinary circuit boards that flash an LED light when receiving a communication signal from another device.
Groups of the devices were tested in a variety of settings in the Seattle area, including inside an apartment building, on a street corner and on the top level of a car park. These locations ranged from less than half a mile away from a TV tower to about 6.5 miles away.
They found that the devices were able to communicate with each other, even the ones farthest from a TV tower. The receiving devices picked up a signal from their transmitting counterparts at a rate of 1 kilobit per second when up to 2.5 feet apart outdoors and 1.5 feet apart indoors. This is enough to send information such as a sensor reading, text messages and contact information.
The researchers were able to demonstrate how one payment card can transfer funds to another card by leveraging the existing wireless signals around them.
The researchers say they plan to continue advancing the capacity and range of the ambient backscatter communication network.