Researchers at the University of Washington have devised a method of wireless communication that allows devices such as brain implants, contact lenses, credit cards and smaller wearable electronics to talk to everyday devices such as smartphones and watches, without needing their own power source.
Dubbed ‘interscatter communication’, the technology 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.
The new technique was described in a paper presented at the annual conference of the Association for Computing Machinery’s Special Interest Group on Data Communication (SIGCOMM 2016) in Brazil. “Wireless connectivity for implanted devices can transform how we manage chronic diseases,” said co-author Vikram Iyer, an 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, these smart contact lenses are too constrained by power demands to send data using conventional wireless transmissions. That means they so far have not been able to send data using 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 electrical engineers and computer scientists has demonstrated for the first time that these types of power-limited devices can ‘talk’ to others using standard Wi-Fi communication. Their system requires no specialised equipment, relying solely on mobile devices commonly found with users to generate Wi-Fi signals using 10 000 times less energy than conventional methods.
The team’s process relies on a communication technique called backscatter, which allows devices to exchange information simply by reflecting existing signals. Because the technique enables inter-technology communication by using Bluetooth signals to create Wi-Fi transmissions, 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.
In one example the team demonstrated, a smartwatch transmits a Bluetooth signal to a smart contact lens outfitted with an antenna. To create a blank slate on which new information can be written, they 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 that can then be read by a smartphone, tablet or laptop.
The challenge, however, is that 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 researchers 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.
“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 those complications,” added co-author 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.”
Beyond implanted devices, the researchers have also shown that their technology can apply to other applications such as smart credit cards. The team built credit card prototypes that can communicate directly with each other by reflecting Bluetooth signals coming from a smartphone. This opens up possibilities for smart credit cards that can communicate directly with other cards and enable applications where users can split the bill by just tapping their credit cards together.
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