Breakthrough backscatter sensor system combines low power and long range
Skin patch
This flexible epidermal patch prototype successfully transmitted information across a 3,300-square-foot atrium. Such a patch could be used to collect and wirelessly transmit medical data. (University of Washington Photo / Dennis Wise)

Researchers at the University of Washington have been working for years on a radio backscatter system that can monitor ultra-low-power sensors wirelessly, and now they’ve fine-tuned the system to pick up signals from more than a mile away.

They say the technology could lead to “smart” contact lenses and skin patches that can track your vital signs and send in the data for instant medical analysis.

And that’s not all: Long-range backscatter sensors might well open up whole new frontiers for the Internet of Things.

“People have been talking about embedding connectivity into everyday objects such as laundry detergent, paper towels and coffee cups for years, but the problem is the cost and power consumption to achieve this,” Vamsi Talla, chief technology officer of Jeeva Wireless, said today in a UW news release. “This is the first wireless system that can inject connectivity into any device with very minimal cost.”

Jeeva Wireless, which was founded by Talla and other UW researchers, is aiming to commercialize the technology within the next few months.

The sensors themselves cost 10 to 20 cents and require only a tiny squirt of electrical power, which can be provided by flexible printed batteries or even ambient radio signals. They encode data by reflecting transmissions that are sent out by a signal emitter and taken in by a receiver.

The challenge has been to figure out how to read the signal reliably over significant distances.

The reflected modulations are so subtle that it’s tricky to detect them amid the background noise of other radio signals. The job gets trickier at greater distances. For example, the range for the smart contact lenses previously developed by the UW team was a mere 3 feet.

To meet the challenge, the UW team used a novel type of modulation known as chirp spread spectrum. The reflected signals were spread across multiple frequencies, which made for much greater sensitivity over longer distances. They also added technological twists to cancel out interference and make it easier for multiple devices to share the spectrum.

Long-range backscatter system
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. (UW Photo / Dennis Wise)

The long-range (“LoRa”) backscatter system can decode a sensor’s signals reliably at distances up to three-tenths of a mile (475 meters) when the sensor is placed anywhere between the signal source and the receiver. And when the sensor is placed right next to the source, the receiver can pick up the data from as far away as 1.7 miles (2.8 kilometers).

The researchers said they successfully tested contact lenses and skin patches in a one-acre farm field, a 3,800-square-foot house and a 13,000-square-foot office space.

Shyam Gollakota, an associate professor at UW’s Paul G. Allen School of Computer Science and Engineering, said sensor manufacturers have had to face tradeoffs between low-power devices and long-distance communication capabilities.

“Now we’ve shown that we can offer both, which will be pretty game-changing for a lot of different industries and applications,” Gollakota said.

The researchers are presenting their paper about the technology this week at the UbiComp 2017 conference in Hawaii. In addition to Talla and Gollakota, the authors of the paper include Mehrdad Hessar, Bryce Kellogg, Ali Najafi and Joshua Smith.

Smart contact lens
The UW team transmitted information across a 3,300-square-foot atrium using this “smart” contact lens prototype. (UW Photo / Dennis Wise)
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