Researchers have discovered a way to capture and harness energy transmitted by such sources as radio and television transmitters, cell phone 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 communications 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 who is leading the research. Tentzeris and his team are using inkjet printers to combine sensors, antennas and energy-scavenging capabilities on paper or flexible polymers. Communications devices transmit energy in many different frequency ranges, or bands.
The team's scavenging devices can capture this energy, convert it from AC to DC, and then store it in capacitors and batteries. The scavenging technology can take advantage presently of frequencies from FM radio to radar, a range spanning 100 megahertz (MHz) to 15 gigahertz (GHz) or higher. That amount of power is enough to operate many small electronic devices, including a variety of sensors and microprocessors. And by combining energy-scavenging technology with super-capacitors and cycled operation, the Georgia Tech team expects to power devices requiring above 50 milliwatts. The Researchers have already successfully operated a temperature sensor using electromagnetic energy captured from a television station that was half a kilometer distant.
Exploiting a range of electromagnetic bands increases the dependability of energy-scavenging devices, explained Tentzeris, who is also a faculty researcher in the Georgia Electronic Design Center at Georgia Tech. At night, when solar cells don't provide power, scavenged energy would continue to increase the battery charge or would prevent discharging. If a battery or a solar-collector/battery package failed completely, scavenged energy could allow the system to transmit a wireless distress signal while also potentially maintaining critical functionalities. The Researchers are utilizing inkjet technology to print these energy scavenging devices on paper or flexible paperlike polymers a technique they already using to produce sensors and antennas. When Tentzeris and his research group began inkjet printing of antennas in 2006, the paper-based circuits only functioned at frequencies of 100 or 200 MHz, recalled Rushi Vyas, a graduate student who is working with Tentzeris and graduate student Vasileios Lakafosis on several projects.
