Drawing power from the air

Researchers have discovered a way to capture and harness energy transmitted by sources like radio and television transmitters, cellphone networks and satellite communications systems. By scavenging this ambient energy from the air around us, the technique could provide a new way to power networks of wireless sensors, microprocessors and communication chips.

“There is a large amount of electromagnetic energy all around us, but nobody has been able to tap into it,” said Manos Tentzeris, a professor in the Georgia Tech School of Electrical and Computer Engineering. Tentzeris and his team are using inkjet printers to combine sensors, antennas and energy-scavenging capabilities on paper or flexible polymers. The resulting self-powered wireless sensors could be used for chemical, biological, heat and stress sensing for the defence sector and the industry; radio frequency identification tagging for manufacturing and shipping, and monitoring tasks in many fields, including communications and power usage.

Communication devices transmit energy in many different frequency ranges, or bands. The team's scavenging devices can capture this energy, convert it from alternating current to direct current and store it in capacitors and batteries. Currently, this technology can take advantage of frequencies from FM radio to radar---a range spanning 100 megahertz to 15 gigahertz or higher.

Scavenging experiments utilising TV bands have already yielded power amounting to hundreds of microwatts, and multi-band systems are expected to generate one milliwatt or more. That amount of power is enough to operate many small electronic devices, including a variety of sensors and microprocessors. By combining energy-scavenging technology with supercapacitors and cycled operation, the Georgia Tech team expects to power devices that require more than 50 milliwatts. In this approach, energy builds up in a battery-like supercapacitor and is it utilised when the required power level is attained.

The researchers have already successfully operated a temperature sensor using electromagnetic energy captured from a TV station that was half a kilometre away. They are preparing another demonstration in which a microprocessor-based microcontroller would be activated simply by holding it in the air.