A team of researchers from University of Washington have demonstrated a device that runs on almost zero power and can transmit data across distances of up to 2.8 kilometers. This demonstration breaks a long-held barrier and potentially enables a vast array of interconnected devices.
For example, 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 - hold great promise for collecting medically relevant data.
But today’s flexible electronics and other sensors that can’t employ bulky batteries and need to operate with very low power typically can’t communicate with other devices more than a few feet or meters away. This limits their practical use in applications ranging from medical monitoring and home sensing to smart cities and precision agriculture.
By contrast, the UW’s long-range backscatter system, which uses reflected radio signals to transmit data at extremely low power and low cost, achieved reliable coverage throughout 4800-square-foot house, an office area covering 41 rooms and a one-acre vegetable farm. The system is detailed in a paper presented on Sept. 13 at UbiComp 2017.
The team’s latest long-range backscatter system provides reliable long-range communication with sensors that consume 1000 times less power than existing technologies capable of transmitting data over similar distances. It’s an important and necessary breakthrough toward embedding connectivity into billions of everyday objects.
The long-range backscatter system will be commercialized by Jeeva Wireless, a spin-out company founded by the UW team of computer scientists and electrical engineers, which expects to begin selling it within six months.
The sensors are so cheap - with an expected bulk cost of 10 to 20 cents each - that farmers looking to measure soil temperature or moisture could affordably blanket an entire field to determine how to efficiently plant seeds or water. Other potential applications range 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.
The research team, for instance, built a contact lens prototype and a flexible epidermal patch that attaches to human skin, which successfully used long-range backscatter to transmit information across a 3300-square-foot atrium. That’s orders of magnitude larger than the 3-foot range achieved by prior smart contact lens designs.
The system has three components: a source that emits a radio signal, sensors that encode information in reflections of that signal and an inexpensive off-the-shelf receiver that decodes the information. When the sensor is placed between the source and receiver, the system can transmit 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 as 2.8 kilometers away.
The advantage to using reflected, or “backscattered,” radio signals to convey information is a sensor can run on extremely low power that can be provided by thin cheap flexible printed batteries or can be harvested from ambient sources - eliminating the need for bulky batteries. The disadvantage is that it’s difficult for a receiver to distinguish these extremely weak reflections from the original signal and other noise.
To overcome the 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 much greater sensitivities and decode backscattered signals across greater distances even when it’s below the noise.
The research was funded by the National Science Foundation.
