Georgia Tech professor Manos Tentzeris holds a sensor (left) and an ultra-broadband spiral antenna for wearable energy-scavenging applications, both of which were inkjet printed on paper. (Source: Georgia Tech)
Radio-frequency energy from television, AM, FM, cellular, WiFi, WiMax, Long-Term Evolution and more can now be harvested to power smarter electronic devices for security, environmental sensing, structural monitoring (bridges/buildings), food spoilage and wearable bio-monitoring devices. Much has been made of the radio-frequency waves saturating every cubic inch of air in developed nations, and especially in metropolitan centers where television, AM, FM, cellular, WiFi, WiMax, Long-Term Evolution and scientific/medical sub-bands compete. One research group at the Georgia Institute of Technology (Atlanta), however, sees RF saturation not as a potential health problem, but as an opportunity to scavenge power directly from the air.
Harvesting RF energy from the air and converting it into usable power for smarter electronic devices could enable always-on security devices that work even during power outages, environmental and structural sensors that do not require batteries, food-preparation sensors that monitor spoilage inside containers, and wearable biological sensors that can transmit vital signs to emergency responders even when the person wearing them is unconscious.
Other groups have demonstrated the ability to harvest ambient RF power using relatively expensive antennas tuned to specific frequencies, but Georgia Tech researchers now claim to have created a cheap ultra-wideband antenna technology that can scavenge a wide swath of frequencies simultaneously and allows their energy-harvesting devices to generate much more power than earlier attempts.
"Using an ultra-wideband antenna that lets us exploit a variety of signals in different frequency ranges is giving us greatly increased power-gathering capability," said Manos Tentzeris, a professor at Georgia Tech.
Since 2006, Tentzeris and colleagues have been experimenting with antenna-based energy-scavenging devices, but only in relatively narrow bands. Now, the team claims to have created ultra-wideband antennas and sensors that can be printed on paper or clear polymers using conductive inks with embedded silver nanoparticles, making their energy-harvesting technology commercially feasible.
In demonstrations, Tentzeris' team has created self-powered sensors for chemical, biological, heat and stress applications. The team has also created ultra-cheap RFID (radio-frequency identification) tags using their techniques, which could be used in manufacturing, shipping and for monitoring communications and power usage.
The system works by first converting alternating RF signals in to direct current that charges either a super-capacitor or a battery, which typically saves up enough energy to power on a device. Only microWatts of power can be generated in real time from a single RF frequency, but by using these new ultra-wideband antennas, milliwatts of power can be produced, enabling some low-power devices to be run directly. Eventually, the team hopes to power devices requiring as much as 50 milliwatts.
Funding was provided by the National Science Foundation, the Federal Highway Administration and Japan’s New Energy and Industrial Technology Development Organization.
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