Prototype of an mm-wave 5G power harvester. These could be used in the future to power IoT devices over 5G networks. (Image Credit: Christopher Moore, Georgia Tech)


For the first time, researchers at the Georgia Institute of Technology developed a small, flexible Rotman lens-based rectifying antenna capable of harvesting 5G frequencies in the 28-GHz band. The new innovative rectenna system uses that tapped energy to power Internet of Things (IoT) devices, turning 5G networks into a wireless power grid.


The Rotman lens is crucial for beamforming networks and is commonly used in radar surveillance systems to create a visualization in multiple directions without moving the antenna system. However, large aperture antennas are needed to collect energy for devices at long ranges. These antennas have a narrowing field of view, limiting their capabilities if distributed from a 5G base station.


The team solved this issue by using a system with a wide-angle of coverage. Electromagnetic energy harvested by the antenna arrays from one direction is combined and delivered into a rectifier. This maximizes the system's efficiency, providing high gain and large beamwidth.


"With this innovation, we can have a large antenna, which works at higher frequencies and can receive power from any direction. It's direction-agnostic, which makes it a lot more practical," said Jimmy Hester, senior lab advisor and the CTO and co-founder of Atheraxon, a Georgia Tech spinoff developing 5G radio-frequency identification (RFID) technology. 

"People have attempted to do energy harvesting at high frequencies like 24 or 35 Gigahertz before," said senior researcher Aline Eid in the ATHENA Lab, established in Georgia Tech's School of Electrical and Computer Engineering. However, those antennas would only work if they had a line of sight to the 5G base station. Until now, it was impossible to boost their area of coverage.


A Rotman lens operates like an optical lens and provides six view levels simultaneously in a spider-shaped pattern. Adjusting the lens shape presents the structure with one curvature angle on both the beam-port and antenna side. The structure maps a set of selected radiation directions to a correlated set of beam-ports. Then, the lens serves as an intermediate component between the receiving antennas and rectifiers to harvest 5G power.


By using this approach, the system achieved a 21-fold boost in harvested power compared to a reference system. It also maintained similar angular coverage.


The team used 3D printers to manufacture the card-sized mm-wave 5G energy harvesters on flexible and rigid substrates. Georgia Tech's new system could pave the way for passive, long-range, mm-wave 5G-powered RFID for wearable IoT devices. 3D and inkjet printing options make the technology inexpensive and accessible to a range of platforms, users, frequencies, and applications.



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