Battery-free IoT sensor feeds off radio waves

Dutch researchers have invented an internet-of-things sensor that powers itself from router radio waves.

The first sample chip measures just 2mm square, weighs 1.6 milligrams and measures temperature. It draws power from a Wi-Fi router via a tiny antenna, takes a reading, and then broadcasts it back, using a slightly different frequency to give the temperature figure.

Peter Baltus, Eindhoven University of Technology professor of wireless technology, points out that because batteries aren't required and the size of the device is so small, it could be mixed in with paint or building materials - something that would make the smart building crowd very happy.

It's also cheap to produce. The chip is built around long-established 65nm process technology, and Professor Baltus estimates that in mass production, the cost per chip could fall as low as 20 cents.

There is one big problem though: range. The prototype sensor has to be within 2.5 centimeters of the router to get enough power to operate. Baltus said the range should be extendable to a meter by the end of the year and has put a theoretical limit of roughly five meters with the current design. If that distance becomes possible, it is feasible that a series of routers and repeaters could be used to power a building-wide temperature map.

The chip was the brainchild of researcher Hao Gao, who received his PhD from the university on Monday for his thesis Fully Integrated Ultra-Low Power mm-Wave Wireless Sensor Design Methods. ®