Interscatter’ tech lets implants talk Wi-Fi

Specifically, the team of UW electrical engineers and computer scientists has demonstrated for the first time that Bluetooth transmissions can be used to create Wi-Fi and ZigBee-compatible signals.

As a result, the new technology can now give power-constrained devices like medical implants the ability to “talk” to other devices using standard Wi-Fi communication.

‘Recycle’ radio signals
Picture tiny devices such as smart contact lenses, brain implants or credit cards, said Vikram Iyer, a UW electrical engineering doctoral student who co-authored the paper. “They can’t use Bluetooth or Wi-Fi chips because they consume too much power in generating their own radio signals.”

Enter the world of “interscatter communication.”

Instead of generating their own radio signals, those “interscatter” devices can “recycle” radio signals transmitted by nearby devices like smart watches.

“We allow a device like a smartwatch or smartphone to do the power expensive generation of radio signals, and then our low-power contact lens, implant or credit card reflects this signal in a way that encodes its own data,” he explained. The transmitter of such interscatter devices isn’t a normal radio. It’s just a switch connected to an antenna, Iyer added.

“Turning on and off this switch allows us to change how the antenna reflects energy. Just by turning on and off this switch at the right rate, our interscatter device is reflecting a Bluetooth signal created by something like a smartwatch to make it look like a Wi-Fi packet that can be received on your phone.”

In one example, the team demonstrated a smartwatch transmitting 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 a way to transform the Bluetooth transmission into a “single tone” signal that can be further manipulated and transformed.

By backscattering that tone signal, the contact lens can encode data — such as health information it may be collecting — into a standard Wi-Fi packet readable by a smartphone, tablet or laptop.

Preserving battery life is paramount for implanted medical devices. “If you have a radio that quickly drains the battery then you might need surgery to replace it,” said Iyer. “Contact lenses are even more extreme in that their tiny batteries may not even be able to power normal Wi-Fi and Bluetooth chip.”

Interscatter enables Wi-Fi for these implanted devices while “consuming only 10,000x less power than a normal Wi-Fi chip,” he added.

Implants that can talk
Many implant devices thus far have been voiceless. Due to their size and location within the body, they have not been able to send data using Wi-Fi to smartphones and other mobile devices.

Giving implanted devices the ability to communicate with others “can transform how we manage chronic diseases,” said Iyer. “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.”

Asked why the team chose to reflect Bluetooth signals, Iyer said, “Because it is widely available on mobile devices and its frequency shift keying protocol makes it easy to use our technique to convert it Wi-Fi.”

He added, “We think Bluetooth to Wi-Fi is cool because of its high data rates, but we have also demonstrated the same technique can convert Bluetooth to Zigbee, or even a different Bluetooth packet.”

Challenges
In developing the intercommunication technology, the team encountered some challenges. Among these issues, the backscattering process creates an unwanted mirror image copy of the signal, which consumes more bandwidth as well as interferes with networks on the mirror copy Wi-Fi channel. But the team developed a technique called “single sideband backscatter” to eliminate the unintended by-product.

“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 co-author and electrical engineering doctoral student Bryce Kellogg in a statement.

The researchers 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.

About the author:

Junko Yoshida is Chief International Correspondent at EE Time