Low power systems often approach reducing power consumption at a software or signal level — that is to say, they may look and work similar to their higher-power counterparts, but save power by reducing performance. But UbiquiTouch, a new project from researchers at Georgia Tech, looks nothing like its peers, and is a totally new approach to low power wireless touch-based systems. Using ambient light for power and FM backscatter for communication, it manages a totally wild average power consumption of just 30.91 μW. The core functionality UbiquiTouch is bringing touch interfaces into spaces computing isn’t usually possible. And the team's demos (ranging from posters to clothing) show a wide variety of potential uses for the technology.
Physically, the system is built from a custom touchpad and low powered circuit. The touchpad is a matrix of conductive pads that act as electrodes, taking advantage of the conductivity of human skin to map touch position. When pads are connected through a finger, the location of that touch, represented as a binary address of the row and column, hits a binary encoder. Using a binary encoder means all pads can be read simultaneously instead of polling each pad individually — saving some of that precious 30.91 μW of power.
Most systems try to generate their wireless signals with as little power as necessary, but wireless communication is almost always a large power draw relative to the rest of a system. UbiquiTouch escapes this issue by using backscattering rather than generating a wave of its own. To do this, it uses ambient FM radio waves (whatever broadcasts happen to be floating through the airwaves around the device), modulates the signal to encode touch and position data, then reflects it back out to the surroundings. From there, an FM receiver in a mobile phone captures the transmitted information and sends it to a computer for processing.
The team built UbiquiTouch into some demo applications, showing a seriously wide scope of use. Because UbiquiTouch doesn’t require batteries or any external hardware, its well positioned for use in smart-textile applications. The most compelling demo though is with touch input from paper, letting users interact with traditionally static interfaces like posters and flyers in new ways.
One limitation (and space for future exploration) is that though the data is received by a phone, it requires a second computer for processing. The team says this is just a product of Android’s limitation on third-party app access to FM audio. They note that this isn't a limit of their technology, and perhaps a rooted device would allow for a fully mobile based system.
For more on UbiquiTouch, you can check out the paper, UbiquiTouch: Self Sustaining Ubiquitous Touch Interfaces, in the 2020 Proceedings of the ACM on Interactive, Mobile, Wearable and Ubiquitous Technologies.