University of Washington

SEATTLE, WA – No power? No problem.

For the first time, University of Washington researchers have demonstrated how devices running on virtually no power can send data across as much ash 2.8 kilometers potentially enabling a vast array of interconnected devices.

From the motion-capture knee patches for arthritic patients to patches that detect exhaustion in athletes through their sweat, flexible electronics hold some of the greatest promise for collecting medical data.

With no room for large batteries, these types of electronics have to operate at low power and cannot communicate more than a few feet away – making them impractical outside of a laboratory.

Meanwhile, the UW’s long-range backscatter system uses reflected radio signals to transmit data at very low power and a small cost, providing coverage for a 4800-square-foot house, a 41 room office, and a one-acre vegetable farm.

Built into an epidermal patch, the UW team could collect and wirelessly transmit medical data across a 3,300 square-foot atrium.

The team’s latest long-range backscatter system provides long-range communication with sensors consuming 1000 times less power than current technologies transmitting the same data over similar distances.

The long-range backscatter system uses a source that emits a radio signal, low-power sensors that encode information in reflected signals and an off-the-shelf receiver.

Three components make up the system – a source to emit a radio signal, a sensor to encode data reflected by signals, and a cheap off-the-shelf receiver to decode the data.

When the sensor is placed between the source and receiver, the system can broadcast data up to 475 meters away. When a sensor placed next to the signal source, the receiver can decode data of up to 2.8 kilometers away

Using reflected radio signals to send data may allow a sensor to eliminate the need for bulky batteries, but its receiver may not be able to distinguish weak reflections from the original signal and other ambient sound.

Mehrdad Hessar, a UW Paul Allen School doctoral student, said that the technology will be able to decode even the softest words that might be as inaudible as the sound of a conversation behind a thick wall.

The UW team’s new type of modulation — chirp spread spectrum — can spread the reflected signals across multiple frequencies to decode backscattered signals across greater distances even when it’s below the noise.

The long-range backscatter system will be brought to market by Jeeva Wireless, a company founded by the UW team of computer scientists and electrical engineers in the next six months.

With an expected bulk cost of 10 to 20 cents each, the sensors are cheap enough that farmers wanting to measure soil temperature or moisture could cover an entire field to efficiently plant seeds or water. Its other applications range from sensor arrays to monitor pollution, noise, traffic, or wireless medical devices which could transmit information about a heart patient’s condition in real time.

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