A few years ago, Aline Eid was sitting in a restaurant sharing popcorn with Jimmy Hester. They weren’t just snacking, though. They were puzzling over a tough problem. How could they tap into the power of invisible signals that send data to cell phones, computers and other devices? If they could manage this, people might someday run their electronics without batteries or cords. As they brainstormed, an idea took shape. That idea has now become a reality.
The heart of their innovation is a special gadget. It helps gather wireless signals sent out by cell-phone towers. Called a Rotman lens, the device looks a bit like a flat metal spider. “We were so excited. I knew it was going to work,” recalls Eid. She’s a PhD student in electrical engineering at the Georgia Institute of Technology in Atlanta.
Hester is the cofounder of the tech company Atheraxon. It’s also in Atlanta. He and Eid shared the idea with their professor, Manos M. Tentzeris. “That was a breakthrough solution,” Tentzeris says. The three described their new device January 12 in Scientific Reports.
The harvesting of wireless energy doesn’t work well over long distances. It’s a problem that electrical engineer Hina Tabassum also knows well. At York University in Toronto, Canada, she works on this problem, too.
Radio waves and microwaves carry data from cell-phone towers to our phones and other devices. The area each tower covers is called a cell. Your cell phone contacts the nearest tower to exchange data. The first cellular networks used radio waves to send and receive data. Newer 5G networks now use higher frequency microwaves. These waves can carry more data and transmit it faster. While that can help save energy, these waves don’t reach as far. That’s because buildings and other objects block them. Moisture in the atmosphere absorbs them, too, reducing their strength the farther they travel.
When waves of energy wash over a phone or other device, they drop off data and then continue on their way. The energy that had been used to carry those data has no use now. It’s a waste, says Tentzeris — unless the new device transforms it into electricity.
This energy tapping is possible across the electromagnetic spectrum. But “you cannot get a lot of power out of low frequencies,” says Eid. Millimeter-range 5G is exciting because cell towers use much more energy to blast out these high frequencies. So a harvesting antenna could get more electricity out of these signals.
A typical 5G tower sends microwave signals out some 180 meters (590 feet). To gather their energy from the edge of this distance, a receiving antenna must point in the exact same direction from which the waves are coming. Yet to be practical, Eid notes, a 5G-energy harvester should work from anywhere within a 5G cell and no matter which way the receiver is pointing. Eid and Hester had been pondering how to harvest energy from such distance and from lots of different directions.
They solved the problem with that Rotman lens. These have been around for a long time. But engineers had only used them to send signals, not to receive them. Says Tabassum, using them as a receiver is “a new technology, for sure.”
The lens looks a bit like a flattened metal tarantula. Spidery “legs” extend from two sides of a central body. On one side, these legs lead to eight small antennas. On the other side, they lead to six beam ports. The antennas catch microwaves and focus them onto a single point at one of those beam ports — whichever one lines up best with the direction of the incoming waves. Another part in the device transforms the microwaves it receives into electrical power.
The six beam ports are like six of the eight eyes on a real tarantula’s head. With them, Eid says, “our system can also look in six different directions.”
The researchers tested their device in the lab across a distance of 2.8 meters (9 feet). They weren’t able to test it at the same high energies a 5G tower would use. But they gathered enough information to simulate how the device should work in the real world. At 180 meters, they now report, this device could deliver six microwatts of power.
Tabassum worries that this estimate might be too high. Her main concern is that things such as buildings, trees and people would block signals, limiting how much of this energy reaches a device.
Tentzeris says his team accounted for that. The Georgia Tech team is now planning to test the device at even longer distances.
The Internet of Things
Six microwatts is not much power. Charging the typical battery for one of today’s cell phones needs around 6 million microwatts (6 watts) of power. Still, the new invention would have enough power to run most sensors and microchips.
As the Internet of Things is emerging, sensors and microchips are spreading everywhere. Low-power electronics can measure air or soil quality. They can keep tabs on safety aspects of bridges or buildings. They can manage the heat or lighting in a home and even track someone’s health. But the batteries that power these electronics contain heavy metals that aren’t easy to make or to dispose of safely. Finding a way to power the Internet of Things without batteries would be good for the environment, says Eid.
Her team figured out how to make its new device at low cost, mainly by using an inkjet printer. They hope to start marketing it as a product within the next few years.
Will they name it “The Tarantula”? Probably not. But Eid does say it has one more thing in common with spiders. “A tarantula can climb anywhere,” says Eid. The device is lightweight and bendable. You can put it anywhere you want, like a sticker — a very special playing-card-sized sticker that grabs energy from the air!
This is one in a series presenting news on technology and innovation, made possible with generous support from the Lemelson Foundation.