The technique could enable “vast arrays” of interconnected sensors for everything from farming to wearables, said the engineers from the University of Washington (UW) in the US.
The team said it used reflected radio signals to transmit data at extremely low power and low cost. The almost-3km range is far wider than for sensors with similar power levels, said the team. Equivalent devices would need 1,000 times as much power to hit the same range, the researchers added.
The system is “an important and necessary breakthrough toward embedding connectivity into billions of everyday objects,” said the researchers.
Ultra-low power devices are a "growing area" in sensor technology, said Peter Harrop, chairman of analysts IDTechEx, to Professional Engineering. “They only need to wake up to do a job sometimes, so you only need little amounts of energy,” he said.
The low power demand means the devices could run on cheap, thin and flexible printed batteries or harvest energy from ambient sources, said the UW team. The sensors’ compact and low-cost ($0.10-20) nature means they could be “injected” into any number of everyday devices, added the researchers.
The engineers built a smart contact lens prototype and a flexible epidermal patch, which transmitted across a 307m2 atrium – far further than a prior maximum range of about 1m. Other uses could include temperature and moisture sensors for farmers, pollution monitors, and medical devices transmitting information about a patient’s heart around the clock.
“Until now, devices that can communicate over long distances have consumed a lot of power. The trade-off in a low-power device that consumes microwatts of power is that its communication range is short,” said assistant professor Shyam Gollakota from the Paul G Allen School of Computer Science and Engineering at the University of Washington. “Now we've shown that we can offer both, which will be pretty game-changing for a lot of different industries and applications.”
The team’s system has three components: a radio signal source, sensors that encode information in reflections of the signal, and an inexpensive receiver which decodes the information. They introduced a new type of modulation – called chirp spread spectrum – into the “backscatter” design, spreading the reflected signals across multiple frequencies and achieving greater sensitivity and range.
The researchers plan to commercialise their system with Jeeva Wireless, a company founded by UW computer scientists and electrical engineers.
The research was published online.