Researchers at the Georgia Institute of Technology have devised a novel way to harvest 5G frequencies at 28GHz to power IoT nodes, in effect turning them into a “wireless power grid.”

The Rotman lens-based rectifying antenna (dubbed the rectenna) was developed such that it could be produced on a flexible substrate with 3D printing, and thus easily incorporated into an IoT node.

The Rotman lens is key for beamforming networks and is frequently used in radar surveillance systems to see targets in multiple directions without physically moving the antenna system.

The inkjet-printed prototype of a mm-wave harvester allows devices to pull energy from 5G wireless communication systems out of the air and convert it into electricity. (Source: Christopher Moore, Georgia Tech)

However, the researchers point out, to harvest sufficient power to supply low-power devices at long ranges, large aperture antennas as needed. The drawback with large antennas, unfortunately, is that they have a narrowing field of view. This prevents their operation if the antenna is widely dispersed from a 5G base station.

According to Aline Eid, a senior researcher at the Athena lab within Georgia Tech’s School of Electrical and Computer Engineering, “we have solved the problem of only being able to look from one direction with a system that has a wide area of coverage. People have attempted to do energy harvesting at high frequencies like 24 or 35GHz before.” And she added such antennas only worked if they had line of sight to the 5G base station; there was no way to increase their angle of coverage till now. “It also does not matter which way it is pointing.”

With this innovation, it is feasible to use a large antenna, which works at higher frequencies and can receive power from any direction, the researchers note.

Operating just like an optical lens, the Rotman lens provides six fields of view simultaneously in a pattern shaped like a spider. Tuning the shape of the lens leads to a structure with a single angle of curvature on the beam-port side and another on the antenna side.

The researchers say this innovative set-up   allows the structure to map a set of selected radiation directions to an associated set of beam-ports.

In this way, the lens is used as an intermediate component between the receiving antennas and the rectifiers, and thus capable of 5G energy harvesting.

A series of demonstrations of the technology indicates a 21-fold increase in harvested power compared    with a referenced counterpart, while maintaining exactly the same angular coverage.

The results were announced in a paper submitted to Scientific Reports earlier this year, where the authors acknowledge their  research was given a major boost when the FCC authorized that 5G can focalize power much more densely than was allowed in previous generations of cellular networks.

“The fact is 5G is going to be everywhere, especially in urban areas. You can replace millions, or tens of millions, of batteries of wireless sensors” noted Emmanouil Tentzeris, a Professor focusing on Flexible Electronics at Georgia Tech. He predicts that power as a service will be the next big application in the telecoms industry, just as data surpassed voice services as the main revenue generator.

Georgia Tech researchers Aline Eid (c.), Manos Tentzeris (l.), and Jimmy Hester (r.) (Source: Christopher Moore, Georgia Tech)

Another contributor to the project, Jimmy Hester, noted that with  the flexible antenna, all the electromagnetic energy collected by the antenna arrays from one direction is combined and fed into a single rectifier, maximizing efficiency. Hester is the senior lab advisor, and also the CTO and co-founder of Atheraxon, a spin-out from the University focusing on 5G RFID technology.

“I have been working on energy harvesting conventionally for at least six years, and for most of this time it did not seem like there was a key to make energy harvesting work in the real world,  because of the FCC limits on power emission and focalization. With the advent of 5G networks, this could actually work and we have demonstrated it. That is extremely exciting – we could get rid of batteries,” said Hester.

The researchers also suggest the technology could open the door to new passive and long-range mm-Wave 5G powered RFID’s for wearable applications.

They used in-house additive manufacturing to print the palm-sized mm-wave harvesters on a multitude of flexible and rigid substrates.

And providing 3D and inkjet printing options will only make the system more affordable and accessible to a broad range of users, platforms, frequencies and applications, the researchers stress.