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Device captures energy in the air

Researchers have created a device to capture and harness energy in the air transmitted by things such as radio and television networks, cell phone towers and satellite communications systems.
Image: Image of energy harvesting device
Georgia Tech School of Electrical and Computer Engineering professor Manos Tentzeris displays an inkjet-printed rectifying antenna used to convert microwave energy to DC powerGary Meek

Researchers have created a device to capture and harness energy in the air transmitted by things such as radio and television networks, cell phone towers, and satellite communications systems.

"There is a large amount of electromagnetic energy all around us, but nobody has been able to tap into it," Manos Tentzeris, a professor of electrical and computer engineering at the Georgia Institute of Technology in Atlanta, said in a news release.

Communications devices transmit energy in many different frequency ranges, or bands. The team's scavenging devices can harvest this energy, convert it from AC to DC power, and then store it in batteries.

Previous work on this concept has produced devices that can harvest energy from a small slice of the electromagnetic spectrum, such as ambient WiFi signals. The new technology captures frequencies ranging from FM radio to radar, spanning 100 megahertz to 15 gigahertz, according to the researchers.

The energy captured is minute — measured in microwatts and milliwatts, not megawatts — but is sufficient to help power networks of wireless sensors, microprocessors, and communications chips.

The technology could be used, for example, at airports where radar and communications sources put out plenty of ambient energy to harvest and power wireless sensors that could detect explosives or nuclear material.

Sensors on food could scan for chemicals that indicate spoilage and send out an alert when detected, increasing food safety.

Tentzeris and his team are using inkjet printers to combine sensors, antennas, and energy scavenging capabilities on paper or flexible polymers.

To print electrical components and circuits, the researchers use a standard materials inkjet printer, but use a special recipe containing silver nanoparticles in an emulsion.

The approach enables the team to print RF components and circuits as well as sensing devices based on nanomaterials such as carbon nanotubes.

Scavenging experiments utilizing TV bands have yielded power amounting to hundreds of microwatts and multiband systems are expected to yield one milliwatt or more. That amount of power is enough to operate small electronic devices, such as sensors.

The team successfully operated a temperature sensor using electromagnetic energy captured from a television station that was a third of a mile away. Self-powered, wireless paper-based sensors will soon be available at very low cost, they said.

The technology was demonstrated July 6 at the IEEE Antennas and Propagation Symposium in Spokane, Wash.

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