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RF Energy Harvesters Gain Interest

By John Blyler
Imagine pulling energy out of thin air and from significant distances from the source? This is one of the energy harvesting technologies that is being studies by Imec.

Radio Frequency (RF) energy harvesters are different from typical induction charging systems like popular “power mats” an electric toothbrushes that require a nearby power source. The close proximity of the power sources it needed to ensure an efficient transfer of power—usually within millimeters.

RF energy harvester work over a much larger distance, from about 10 to 15 meters, and and at much higher frequencies that typically are in the GSM mobile radio band. The key to successful RF power transfer lies in the design of the antenna system, explained Jan Van der Kam, program director for the sensors and energy harvester group at Imec.

“We are looking at antennas that direct the RF energy much more efficiently instead of spreading it in all directions,” Kam said at the recent Imec Technology Forum (ITR) held in Leuven, Belgium. Imec is working on designing more efficient antennas but also developing the feedback mechanism for the energy receptors. This feedback approach will help to increase the efficiency of the energy transfer to even greater distance.

Application areas for this technology would include everything from smart buildings, where the energy could be generated locally and transferred without wires, to recharging a hearing-aid battery. As a proof-of-concept, Imec acquired a small weather station that was successfully powered at a distance using RF energy harvesters.

Energy harvesting, or scavenging, has become a lucrative topic of late. The slow improvement in battery technology, estimated at about 3% to 5% per year, plus the added functionality and performance requirements of mobile devices has created a need for both architectural changes to improve SoC efficiency and new ways to generate energy. But the architectural changes can be difficult and expensive to implement. While voltage islands and dark silicon are well-discussed, companies are just beginning to work with more exotic approaches such as near-threshold computing. Being able to generate energy could postpone the need to move to those techniques while also saving costs.

Most approaches focus on movement or light to generate that energy, but pulling energy out of thin air isn’t a new concept. At the turn of the 20th century, Nikola Tesla proposed using wireless power and even set up a laboratory in Wardenclyffe, N.Y., to turn that idea into a reality. More than a century later, the idea appears to have some merit.

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