Rotman lens-based rectenna harvests 28 GHz energy for IoT devices

March 30, 2021 // By Jean-Pierre Joosting
Rotman lens-based rectenna harvests 28 GHz energy for IoT devices
Breakthrough leverages a Rotman lens-based rectifying antenna or rectenna capable of millimeter-wave harvesting at 28 GHz.

Researchers at the Georgia Institute of Technology have developed a flexible Rotman lens-based rectifying antenna (rectenna) system that is able to harvest millimeter-wave energy  in the 28-GHz band. The rectenna can be used to tap into the over-capacity of 5G networks, turning them into “a wireless power grid” for powering Internet of Things (IoT) devices.

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.

However, to harvest enough power to supply low-power devices at long ranges, large aperture antennas are required. The problem with large antennas is they have a narrowing field of view, curtailing their operation as the antenna becomes more widely dispersed from a 5G base station.

“We’ve solved the problem of only being able to look from one direction with a system that has a wide angle of coverage,” said senior researcher Aline Eid in the ATHENA lab, established in the Georgia Tech School of Electrical and Computer Engineering.

“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,” noted Jimmy Hester, senior lab advisor and the CTO and co-founder of Atheraxon, a Georgia Tech spinoff developing 5G RFID technology. 

With the Georgia Tech system, all the electromagnetic energy collected by the antenna arrays from one direction is combined and fed into a single rectifier, which maximizes its efficiency. 

“People have attempted to do energy harvesting at high frequencies like 24 or 35 Gigahertz before,” Eid said, but 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 until now.

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 results in a structure with one angle of curvature on the beam-port side and another on the antenna side. This enables the structure to map a set of selected radiation directions to an associated set of beam-ports. The lens is then used as an intermediate component between the receiving antennas and the rectifiers for 5G energy harvesting.

This approach addresses the tradeoff between rectenna angular coverage and turn-on sensitivity with a structure that merges unique RF and DC combination techniques, thereby enabling a system with both high gain and large beamwidth.

In demonstrations, the rectenna achieved a 21-fold increase in harvested power compared with a referenced counterpart, while maintaining identical angular coverage.

The researchers used inhouse additive manufacturing to print the palm-sized mm-wave harvesters on a multitude of everyday flexible and rigid substrates. Providing 3D and inkjet printing options will make the system more affordable and accessible to a broad range of users, platforms, frequencies, and applications.

“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, especially for smart city and smart agricultural applications,” said Emmanouil (Manos) Tentzeris, Ken Byers Professor in Flexible Electronics in the School of Electrical and Computer Engineering.

Tentzeris predicts that power as a service will be the next big application for the telecom industry, just as data overtook voice services as a major revenue producer.

The research team envisge the prospect of service providers embracing this technology to offer power on demand “over the air,” eliminating the need for batteries. The technology may also open the door for new passive, long-range, mm-wave 5G-powered RFID for wearable and ubiquitous IoT applications.

 

Reference

A. Eid, et al., “5G as a wireless power grid.” (Scientific Reports, 2021) https://doi.org/10.1038/s41598-020-79500-x

Picture: 
A Georgia Tech ATHENA group member holds an inkjet-printed prototype of a mm-wave harvester. The researchers envision a future where IoT devices will be powered wirelessly over 5G networks. (Photo credit: Christopher Moore, Georgia Tech)

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