Tech Briefs

Implanted and wearable electronics reflect signals for ultra-low-power communication.

University of Washington (UW) engineers have introduced a new way of communicating that allows devices such as brain implants, contact lenses, and smaller wearable electronics to talk to everyday devices like smartphones and watches. This new “interscatter communication” works by converting Bluetooth signals into Wi-Fi transmissions over the air. Using only reflections, an interscatter device such as a smart contact lens converts Bluetooth signals from a smartwatch, for example, into Wi-Fi transmissions that can be picked up by a smartphone.

“Interscatter communication” generates low-power Wi-Fi transmissions using everyday mobile devices. In one example, Bluetooth signals from a smartwatch (left) transmit data from a neural device that can be implanted in a patient’s brain (right) to a smartphone via Wi-FI. (Credit: Mark Stone, University of Washington)

“Wireless connectivity for implanted devices can transform how we manage chronic diseases,” said Vikram Iyer, a UW electrical engineering doctoral student. “For example, a contact lens could monitor a diabetic’s blood sugar level in tears and send notifications to the phone when the blood sugar level goes down.”

Due to their size and location within the body, the smart contact lenses are too constrained by power demands to send data using conventional wireless transmissions. That means that so far they have been unable to send data over Wi-Fi to smartphones and other mobile devices. Those same requirements also limit emerging technologies such as brain implants that treat Parkinson’s disease, stimulate organs, and may one day even reanimate limbs.

The team of UW electrical engineers and computer scientists has demonstrated for the first time that these types of power-limited devices can talk to other devices using standard Wi-Fi communication. Their system requires no specialized equipment, relying solely on common mobile devices to generate Wi-Fi signals using 10,000 times less energy than conventional methods. “Instead of generating Wi-Fi signals on your own, our technology creates Wi-Fi by using Bluetooth transmissions from nearby mobile devices such as smartwatches,” said Vamsi Talla, a recent UW doctoral graduate in electrical engineering who is now a research associate in the Department of Computer Science and Engineering.

How It Works

The team’s process relies on a communication technique called backscatter, which allows devices to exchange information simply by reflecting existing signals. Because the new technique enables intertechnology communication, the team calls it interscattering. Interscatter communication uses the Bluetooth, Wi- Fi, or ZigBee radios embedded in common mobile devices like smartphones, watches, laptops, tablets, and headsets to serve as both sources and receivers for these reflected signals.

The team demonstrated one example in which a smartwatch transmitted a Bluetooth signal to a smart contact lens outfitted with an antenna. To create a blank slate on which new information can be written, the UW team developed an innovative way to transform the Bluetooth transmission into a single-tone signal that can be further manipulated and transformed. By backscattering that single-tone signal, the contact lens can encode data — such as health information it may be collecting — into a standard Wi-Fi packet.

“Bluetooth devices randomize data transmissions using a process called scrambling,” said Shyam Gollakota, assistant professor of computer science and engineering. “We figured out a way to reverse engineer this scrambling process to send out a single-tone signal from Bluetooth-enabled devices such as smartphones and watches using a software app.”

The challenge, however, is that the backscattering process creates an unwanted mirror image copy of the signal, which consumes more bandwidth and interferes with networks on the mirror copy Wi-Fi channel. But the UW team developed a technique called single-sideband backscatter to eliminate the unintended byproduct. “That means that we can use just as much bandwidth as a Wi-Fi network and you can still have other Wi-Fi networks operate without interference,” said electrical engineering doctoral student Bryce Kellogg.

The researchers — who work in UW’s Networks and Mobile Systems Lab and Sensor Systems Lab — built three proof-of-concept demonstrations for previously infeasible applications, including a smart contact lens and an implantable neural recording device that can communicate directly with smartphones and watches.

“Preserving battery life is very important in implanted medical devices, since replacing the battery in a pacemaker or brain stimulator requires surgery and puts patients at potential risk from complications,” said Joshua Smith, associate professor of electrical engineering and of computer science and engineering. “Interscatter can enable Wi-Fi for these implanted devices while consuming only tens of microwatts of power.”

An informational video is available at www.youtube.com/watch?v=MoeFYCGbthk&feature=youtu.be. For more information, visit www.washington.edu/news/.