Chicago, IL – After setting up an RF energy-harvesting demo at this week’s Sensors Expo collocated with ESC Chicago, Powercast’s director of marketing Harry Ostaffe presented a paper that outlined the concepts and paths to what he believes to be the endgame: full ambient RF harvesting capabilities that sip power from ubiquitous mobile networks and eliminate batteries and direct RF power sources completely.
At the start of his presentation, entitled “Power out of thin air: Ambient RF energy harvesting for wireless sensors,” Ostaffe pointed out that the ambient RF energy is actually pretty consistent, and at the companies facility outside Pittsburgh, it’s typically in the – 25 to -20 dBm range (-20 dBm is 0.01 mW) thanks to a call tower located 900 feet away.
At 100 m from the typical 100-W basestation, Ostaffe said there is typically 800 microWatts/meter squared available, and at 500 m that drops to 32 microW, or to 8 microW at 1000 m.
”There is sufficient power provided from overall mobile networks for low-power sensors,” he said. The target applications for ambient RF devices primarily revolve around wireless sensor nodes.
Though Ostaffe is convinced the company is almost there, thanks to increasingly efficient power conversion and signal-processing technologies, he awaits advances in lower-power comparators, as well as the emergence of 1-V-or-less MCUs to allow the elimination of boost converters, thereby reducing conversion losses. The company is currently evaluating the 0.9-V MCU announced by Silicon Labs last year.
Also, in order to fully take advantage of mobile networks, “multiband and broadband capability would be a very beneficial capability,” he said. This would allow the ambient RF harvester to pull energy from a broader range of networks and active channels.
Wireless power over 35 feet
While Ostaffe awaits the advances he believes are just around the corner to enable full RF ambient-energy harvesting, the demo at Sensors Expo did not go that far, and instead comprised a 4-W Powercaster transmitter (EIRP) operating using spread-spectrum techniques in the 915-MHz band that transmitted RF power over 35 feet to the P2110 batteryless Powerharvester receiver.
Announced last month, along with the battery-enabled P1110 Powerharvester receiver, the P2110 extracted -11 dBm (approximately 0.1 mW) of power and provided up to 5.25 V (regulated).
With directed RF power technology, Ostaffe is hoping to completely eliminate the need for new cabling for industrial, smart grid, defense, structural monitoring and other applications, with key advantages including one-to-many charging, controllable wireless power, no more battery changes, zero maintenance and the ability to completely seal embedded devices for underwater or otherwise inclement environments.
For more information, go to the company’s data center at Powercast PDFs.