Scientists Create Material That Can Charge Phones with Wi-Fi
Matthew Greenwood posted on February 13, 2019 |
Bendable rectenna harvests energy from wireless Internet waves.

Researchers at MIT may have taken a big step toward creating a world where electronic devices can be charged wirelessly.

As reported in Nature, a team led by researcher Tomas Palacios has created an atoms-thin, bendable material that absorbs wireless Internet and other electromagnetic waves from the air and converts them into an electrical charge. It is the latest development in a technology known as “rectennas,” which convert AC electromagnetic waves into DC electricity.

Conventional rectennas are rigid and fragile instruments that, though cheap enough to produce small devices, can be prohibitively expensive on a large scale. Some flexible rectennas have been created, but they operate at too low a frequency to capture gigahertz signals that phones and Wi-Fi use.

Palacios’ team created a rectenna that uses a flexible radio frequency antenna that can capture electromagnetic waves as AC waveforms. The antenna is connected to a sheet of molybdenum disulphide, a new 2D material that is mere atoms thick—making it one of the thinnest superconductors in the world. The semiconductor converts the AC signal into DC voltage.

The result is a flexible, battery-free device that passively collects the Wi-Fi signals that are all around us and converts them into usable DC power. The material can also be produced in a roll-to-roll process to cover very large areas.

“When you have one of these energy-harvesting devices you are collecting energy 24/7 and you could be storing that in a battery to use later,” said Palacios.

So far, the new rectenna can produce about 40 microwatts of power when exposed to typical Wi-Fi signals (about 150 microwatts) in the lab. It’s a far cry from the 60 watts a typical computer needs to operate but would be enough to power Internet of Things sensors, which only require a few microwatts to light up a simple display or power a silicon chip. Or, the energy could be stored in a battery.

Another promising field of use is in medical devices. Because Wi-Fi and similar radio frequency signals pass through tissue, implants could be powered by the new rectenna to send health data to a receiver from inside the body.

The team is now planning to build more complex systems and improve the rectenna’s ability to harvest and release power.

“In the future, everything is going to be covered with electronic systems and sensors. The question is going to be how do we power them?” said Palacios. “This is the missing building block that we need.”

Want to read more about technological advances in rectennas? Check out Two Steps Closer to Harnessing Waste Heat for Energy Production.

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