91探花 researchers have demonstrated for the first time that devices that run on almost zero power can transmit data across distances of up to 2.8 kilometers 鈥� breaking a long-held barrier and potentially enabling a vast array of interconnected devices.
For example, flexible electronics 鈥� from knee patches that capture range of motion in arthritic patients to patches that use sweat to detect fatigue in athletes or soldiers 鈥� hold great promise for collecting medically relevant data.
But today鈥檚 flexible electronics and other sensors that can鈥檛 employ bulky batteries and need to operate with very low power typically can鈥檛 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鈥檚 , 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 to be presented Sept. 13 at .
鈥淯ntil 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,鈥� said , lead faculty and associate professor in the Paul G. Allen School of Computer Science & Engineering. 鈥淣ow we鈥檝e shown that we can offer both, which will be pretty game-changing for a lot of different industries and applications.鈥�
The team鈥檚 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鈥檚 an important and necessary breakthrough toward embedding connectivity into billions of everyday objects.
The long-range backscatter system will be commercialized by , a spin-out company founded by the 91探花team of computer scientists and electrical engineers, which expects to begin selling it within six months.
The sensors are so cheap 鈥� with an expected bulk cost of 10 to 20 cents each 鈥� 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 鈥渟mart鈥� cities or medical devices that could wirelessly transmit information about a heart patient鈥檚 condition around the clock.
鈥淧eople 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,鈥� said , CTO of Jeeva Wireless, who was an Allen School postdoctoral researcher and received a doctorate in electrical engineering from the UW. 鈥淭his is the first wireless system that can inject connectivity into any device with very minimal cost.鈥�
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鈥檚 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 鈥渂ackscattered,鈥� 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 鈥� eliminating the need for bulky batteries. The disadvantage is that it鈥檚 difficult for a receiver to distinguish these extremely weak reflections from the original signal and other noise.
鈥淚t鈥檚 like trying to listen to a conversation happening on the other side of a thick wall 鈥� you might hear some faint voices but you can鈥檛 quite make out the words,鈥� said , an Allen School doctoral student. 鈥淲ith our new technology we can essentially decode those words even when the conversation itself is hard to hear.鈥�
To overcome the problem, the 91探花team introduced a new type of modulation 鈥� called 鈥� 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鈥檚 below the noise.
鈥淲e basically started with a clean slate and said if what we really need to enable smart applications is long-range communication, how could we design the system from the ground up to achieve that goal?鈥� said , a co-founder at Jeeva Wireless who was a 91探花electrical engineering student.
The research was funded by the National Science Foundation.
Co-authors include , professor in the Allen School and the 91探花Department of Electrical Engineering, and 91探花electrical engineering doctoral student .
For more information, contact the research team at longrange@cs.washington.edu.