Massachusetts Institute of Technology researchers and their colleagues have taken a step toward electronics powered not by batteries, but by Wi-Fi signals.
In a study just published in the journal Nature, the researchers demonstrate a new type of "rectenna" – the name given to devices that convert AC electromagnetic waves into DC electricity. This one uses a flexible radio-frequency (RF) antenna to capture electromagnetic waves, including those carrying Wi-Fi, as AC waveforms. The signal travels into a two-dimensional semiconductor with a thickness of just a few atoms; there, it is converted into DC voltage that can power electronic circuits or recharge batteries.
One of the main advantages of such a setup is that, to function, it needs only to passively capture signals that are already ubiquitous. In addition, its flexible nature allows roll-to-roll process fabrication that can cover very large areas.
Paper coauthor Tomás Palacios, an MIT professor, suggested a vision for future electronics systems that could take advantage of this type of deployment: systems that wrap around a bridge or highway, for instance, or cover the walls of an office. From that starting point, he said, electronic intelligence can be brought “to everything around us.”
For the nearer future, the rectenna could be used to power flexible and wearable electronics, IoT sensors and data communications of implantable medical devices – such as the pills now being developed that can be swallowed by patients and used to stream diagnostic health data back to a central computer system.
In fact, medical devices represent an area with a strong need for battery-free power sources. “Ideally you don’t want to use batteries to power these systems,” said paper co-author Jesús Grajal, of the Technical University of Madrid. “If they leak lithium, the patient could die.”
Also of note in the study is the researchers’ use of molybdenum disulfide (MoS2) to build their rectifier – the rectenna component that converts an AC input signal to DC power. The two-dimensional material is one of the world’s thinnest semiconductors, and its property of rearranging to act like a switch when exposed to certain chemicals allows it to act as an ultrafast Schottky diode.
(Discover diodes on Engineering360.)
The work provides a blueprint for other flexible devices that can efficiently convert Wi-Fi to electricity with substantial output. The team is now planning to build more complex systems and improve efficiency.
