Battery-less wearables make debut

November 25, 2016 // By Julien Happich
California-based startup Matrix Industries just came out of stealth mode with a very promising Indiegogo crowd-funding campaign for what may be the first commercially-available battery-less smart watch, leveraging a novel type of thermoelectric units.

Monitoring your activity (calories burned, steps taken) and sleep quality, the PowerWatch as the company calls it is built with power-efficient components such as a 1.2" diameter LCD memory display and Ambiq Micro's ultra-low power Apollo MCU, so it can draw all of its operating power from a small thermoelectric unit that generates electricity out of body heat. Still the device can connect to a smartphone via a built-in Bluetooth 4.0 LE module to wirelessly sync with the MATRIX iOS and Android apps for more in depth data interpretation (peaks, trends).

Calorie counting is performed through a sensor-fusion based algorithm, reading data not only from the voltage information provided by the Seebeck effect (when the wearer's body heats up), but also from two temperature sensors (near the skin and away from it on the outer side of the watch) and from an accelerometer.

But at this early stage of the company's existence, the PowerWatch is really only a public demonstrator, admitted CEO and Co-Founder Akram Boukai when interviewed by EETimes Europe. The bigger story is really about the very low cost and rugged thermoelectric unit that the former academic invented when doing research on clean energy sources in the Chemistry Department of the University of California, Berkeley.

Back in 2008, Boukai and his research colleagues published a paper in Nature, "Silicon nanowires as efficient thermoelectric materials", which was our first hint for this interview.

"Actually we don't use silicon nanowires, this was a lab discovery and a curiosity. We had found that while bulk silicon is a good heat conductor, by processing it into nanowires, its thermal conductivity decreased by a hundred times and became similar to that of glass while retaining a very good electrical conductivity" revealed Boukai.