Researchers at the University of Washington (UW) have developed a way of allowing devices to interact with each other without requiring batteries or wires.
The devices are able to exchange information by reflecting or absorbing pre-existing or "ambient" radio signals, a technique the researchers refer to as "ambient backscatter". The technique makes use of the ubiquitous TV and cellular transmissions surrounding us, in order to exchange information.
The researchers created credit card-sized prototype devices, which were essentially antennae fitted into ordinary circuit boards. The devices were placed within a few metres of each other and flashed an LED light when receiving a signal from a paired device. Testing distances ranged from less than a kilometre from a base TV tower, to approximately 10km away. The rate of data transfer reached up to 1kbps when the devices were 700cm apart outdoors, or 450cm apart indoors, which is fast enough to send information such as text messages, contact information, or a sensor reading.
"Our devices form a network out of thin air," explains Joshua Smith, a UW associate professor of computer science and engineering and of electrical engineering, and co-author of the research group's publication Ambient Backscatter: Wireless Communication Out of Thin Air. "You can reflect these signals slightly to create a Morse code of communication between battery-free devices."
According to the researchers, the technology could develop to the point of enabling networks of devices to communicate without requiring a power source or human attention. "We can repurpose wireless signals that are already around us into both a source of power and a communication medium," says lead researcher Shyam Gollakota, a UW 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 see the technology as enabling the reality of an "Internet of Things", with the potential to equip everyday objects with battery-free tags that enable communication with other devices. For example, a tag attached to keys could send a smartphone signal allowing a user to locate them easily. Battery-free tags could enhance wearable device technology, or be built into battery-reliant devices such as smartphones to enable phones to send text messages even once the battery is dead.
The technology may also have important implications for industry, health, and other fields, by allowing permanent, battery-free sensors to be placed permanently. For example, sensors could be placed in a bridge and programmed to monitor the soundness of the structure, sending an alert if hairline cracks or weakness were detected.
The research paper, which was presented in Hong Kong at the Association for Computing Machinery's Special Interest Group on Data Communication 2013 conference, has received the conference's "best paper" award. The researchers plan to continue working on increasing the capacity and range of the ambient backscatter communication network.
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