A team of scientists from the Massachusetts Institute of Technology (MIT) has developed a flexible device that can convert energy from Wi-Fi signals into electricity, a discovery that could replace the battery needed to power personal electronics.
Using an extremely thin 2D semiconductor, the researchers developed a new kind of rectenna that uses a flexible radio-frequency antenna to capture electromagnetic waves as AC waveforms.
This setup will enable a battery-free device to passively capture and transform ubiquitous Wi-Fi signals into DC power and the flexibility allows the device to be fabricated in a roll-to-roll process that can cover substantially large areas.
“What if we could develop electronic systems that we wrap around a bridge or cover an entire highway, or the walls of our office and bring electronic intelligence to everything around us? How do you provide energy for those electronics?” Tomás Palacios, a professor in the Department of Electrical Engineering and Computer Science and director of the MIT/MTL Center for Graphene Devices and 2D Systems in the Microsystems Technology Laboratories and co-author of the paper, said in a statement. “We have come up with a new way to power the electronics systems of the future—by harvesting Wi-Fi energy in a way that’s easily integrated in large areas—to bring intelligence to every object around us.”
Rectennas generally rely on a rectifier to convert the AC input signal into DC power. This component is traditionally comprised of either silicon or gallium arsenide, which cover the Wi-Fi band, but are rigid and could be expensive if needed to cover larger areas like buildings or walls.
In an attempt to override these problems, researchers have sought a way to produce flexible rectennas. However, thus far they only operate at lower frequencies and cannot capture and convert signals in gigahertz frequencies, where most of the relevant cell phone and Wi-Fi signals are.
Instead of the silicon and gallium arsenide, the researchers used molybdenum disulfide, which is only three atoms thick. The material’s atoms will rearrange when exposed to certain chemicals, forcing a phase transition from a semiconductor to a metallic material in a structure called a Schottky diode.
“By engineering MoS₂ into a 2D semiconducting-metallic phase junction, we built an atomically thin, ultrafast Schottky diode that simultaneously minimizes the series resistance and parasitic capacitance,” first author and EECS postdoc Xu Zhang, who will soon join Carnegie Mellon University as an assistant professor, said in a statement.
Some parasitic capacitance is inevitable in electronics, but the new device features a lower capacitance that results in increased rectifier speeds and higher operating frequencies to capture and convert up to 10 gigahertz of wireless signals.
“Such a design has allowed a fully flexible device that is fast enough to cover most of the radio-frequency bands used by our daily electronics, including Wi-Fi, Bluetooth, cellular LTE, and many others,” Zhang said.
The researchers found through testing that they can produce approximately 40 microwatts of power when exposed to the typical power levels of Wi-Fi signals of about 150 microwatts, enough to power a simple mobile display or silicon chips.
There are a number of potential applications for the flexible device, including for powering of flexible and wearable electronics, medical devices and sensors for the Internet of Things, as well as to power the data communications of implantable medical devices like ingestible pills that can stream health data back to a computer.
“Ideally you don’t want to use batteries to power these systems, because if they leak lithium, the patient could die,” co-author Jesús Grajal, a researcher at the Technical University of Madrid, said in a statement. “It is much better to harvest energy from the environment to power up these small labs inside the body and communicate data to external computers.”
The researchers now plan to construct systems that are more complex and improve the device’s efficiency, which is currently at 40 percent depending on the input power of the Wi-Fi input.
