Battery-free devices harvest energy from RF signals

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9 October 2013 News

Engineers at the University of Washington have created a new wireless communication system that allows devices to exchange information by reflecting or absorbing pre-existing radio frequency signals, enabling them to interact with users and communicate with each other without using batteries. The new technique, which the researchers are calling ‘ambient backscatter’, takes advantage of the TV and cellular transmissions that already surround us, and could enable a network of devices and sensors to communicate with no power source or human attention needed.

“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 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.”

Smart sensors could be built and placed permanently inside nearly any structure, then set to communicate with each other. For example, sensors placed in a bridge could 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, without requiring battery consumption.

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, including inside an apartment building, on a street corner and on the top level of a parking garage. These locations ranged from less than 800 metres away from a TV tower to about 10,5 kilometres away.

It was found that even the devices farthest from a TV tower were able to communicate with each other. The receiving devices picked up a signal from their transmitting counterparts at a rate of 1 kilobit per second when up to 75 cm apart outdoors and 45 cm apart indoors. This is enough to send information such as a sensor reading, text messages and contact information.

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Battery-free devices harvest energy from RF signals

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