Researchers from the University of Washington have demonstrated devices that run on almost zero power can transmit data across distances of up to 2.8 kilometers. This breaks a long-held barrier and potentially enabling an array of interconnected devices.
Flexible electronics – from knee patches that capture range of motion in arthritic patients, to patches that use sweat to detect fatigue in athletes or soldiers – have a lot of promise for collecting medically relevant data.
Today’s flexible electronics and other sensors can’t employ bulky batteries and need to operate with low power typically can’t communicate with other devices for more than a few feet or meters away. This limits practical use in applications ranging from medical monitoring and home sensing to smart cities and precision agriculture.
In contrast, the UW long-range backscatter system uses reflected radio signals to transmit data at very low power and low cost. This achieved reliable coverage throughout a 4800-square-foot house, an office area covering 41 rooms and a one-acre vegetable farm.
"Until now, devices that can communicate over long distances have consumed a lot of power. The tradeoff in a low-power device that consumes microwatts of power is that its communication range is short," said Shyam Gollakota, lead faculty and associate professor in the Paul G. Allen School of Computer Science & Engineering. "Now we've shown that we can offer both, which will be pretty game-changing for a lot of different industries and applications."
The latest long-range backscatter system provides reliable long-range communication with sensors that consume 1000 times less power than the existing technologies. They are capable of transmitting data over similar distances. It is an important breakthrough toward embedding connectivity into billions of everyday objects.
The long-range backscatter system will be commercialized by Jeeva Wireless, a company founded by the UW team of computer scientists and electrical engineers that expects to begin selling it within six months.
The sensors have an expected bulk cost of 10 to 20 cents each. They are so cheap that farmers who are looking to measure soil temperature or moisture could affordably blanket and an entire field to determine how efficiently plant seeds or water. Other potential applications could be from sensor arrays that could monitor pollution, noise or traffic in “smart” cities, or medical devices that could wirelessly transmit information about a heart patient’s condition around the clock.
"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," said Vamsi Talla, CTO of Jeeva Wireless, who was an Allen School postdoctoral researcher and received a doctorate in electrical engineering from the UW. "This is the first wireless system that can inject connectivity into any device with very minimal cost."
The research team built a contact lens prototype and a flexible epidermal patch that attaches to human skin and successfully used long-range backscatter to transmit information across 3300-square-foot-atrium. Orders of magnitude larger than the 3-foot range are achieved by prior smart contact lens designs.
The system has three main components: a source that emits a radio signal, sensors that encode information in reflections of that signal in an inexpensive off-the-shelf receive that decodes information. When the sensor is placed between the source and receiver, the system transmits data at distances up to 475 meters. When the sensor is placed next to the signal source, the receiver can decode information from as far 2.8 kilometers away.
The advantage of using reflected radio signals to convey information is a sensor can run on very low power that can be provided by thin, cheap, flexible printed batteries or can be harvested from ambient sources. This eliminates the need for bulky batteries. The disadvantage of this is that’s it is difficult for a receiver to distinguish the weak reflections from the original signal and other noise.
"It's like trying to listen to a conversation happening on the other side of a thick wall -- you might hear some faint voices but you can't quite make out the words," said Mehrdad Hessar, an Allen School doctoral student. "With our new technology, we can essentially decode those words even when the conversation itself is hard to hear."
To address this problem, the UW team introduced a new type of modulation, called chirp spread spectrum, into its backscatter design. Spreading the reflected signals across multiple frequencies allowed the team to achieve greater sensitivity and decode backscattered signals across great distances even when it’s below the noise.
A paper on this device was presented at UbiComp 2017.