‘Rectenna’ breakthrough sees devices powered by Wi-Fi signal

A new kind of rectenna has been developed that uses a flexible radio-frequency (RF) antenna to capture electromagnetic waves, such as those carried on Wi-Fi signals, and convert them to electrical current.

The discovery could pave the way for a future where devices do not need batteries to be powered or could charge wirelessly without placing them on a plate, which is how current wireless charging methods work.

The rectenna is just a few atoms thick and harvests the signal as AC, which then travels into the semiconductor and is converted into a DC voltage.

The device could be used to provide battery-less power for smartphones, laptops, medical devices and wearable technology, according to the team from the Massachusetts Institute Of Technology (MIT).

Due to its flexibility, it could also be fabricated to cover large areas. This has major implications for the future of “electronic intelligence”, the team said.

Professor Tomas Palacios, director of the Massachusetts Institute of Technology and Microsystems Technology Laboratories Centre for Graphene Devices and 2D Systems, said: “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?

“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.”

In experiments, the rectenna generated about 40 microwatts of power when exposed to typical Wi-Fi signals of around 150 microwatts. This is more than enough to light up a simple mobile display or activate silicon chips.

Spanish co-author Professor Jesus Grajal, from the Technical University of Madrid, said a key application could be in the field of medical implants and ‘pills’ that stream health data after being swallowed by patients.

He added: “Ideally, you don’t want to use batteries to power these systems, because if they leak lithium, the patient could die.”

To create the rectenna, the team used a novel 2D material called molybdenum disulphide, which at three atoms thick is one of the world’s thinnest semiconductors.

All antennas produce electricity, but normally in very tiny amounts. In a portable radio, for instance, an amplifier boosts the signal to allow broadcasts to be heard. The amplifier needs a suitable power source, such as a battery.

The electricity obtained from radio waves comes in the form of a high-frequency alternating current (AC). In the new device, the semiconductor converts the AC signal into a more usable direct current.

The team is now planning more complex devices with improved efficiency.

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