Georgia Tech graduate student Rushi Vyas (front) holds a prototype energy-scavenging device, while School of Electrical and Computer Engineering professor Manos Tentzeris displays a miniaturized flexible antenna that could be used for broadband energy-scavenging devices. Georgia Tech Photo: Gary Meek
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,” says Manos Tentzeris, a professor in
the Georgia Tech School of Electrical and Computer Engineering who is leading
the research. “We are using an ultra-wideband antenna that lets us exploit
a variety of signals in different frequency ranges, giving us greatly increased
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 defense and industry; radio-frequency
identification (RFID) tagging for manufacturing and shipping; and monitoring
tasks in many fields including communications and power usage.
A presentation on this energy-scavenging technology was delivered at the IEEE
Antennas and Propagation Symposium.
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 MHz to 15 GHz or higher.
Georgia Tech School of Electrical and Computer Engineering professor Manos Tentzeris holds a sensor (left) and an ultra-broadband spiral antenna for wearable energy-scavenging applications. Both were printed on paper using inkjet technology. Georgia Tech Photo: Gary Meek
Scavenging experiments using 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.
And by combining energy-scavenging technology with super-capacitors and
cycled operation, the Georgia Tech team expects to power devices requiring
above 50 mW. In this approach, energy builds up in a battery-like
super-capacitor and is used when the required power level is reached.
The researchers have already successfully operated a temperature sensor
using electromagnetic energy captured from a television station that was half a
kilometer distant. They are preparing another demonstration in which a
microprocessor-based microcontroller would be activated simply by holding it in
Exploiting a range of electromagnetic bands increases the dependability of
energy-scavenging devices, explains Tentzeris. If one frequency range fades
temporarily due to usage variations, the system can still exploit other
The scavenging device could be used by itself or in tandem with other
generating technologies. For example, scavenged energy could assist a solar
element to charge a battery during the day. At night, when solar cells don’t
provide power, scavenged energy would continue to increase the battery charge
or would prevent discharging.
Using ambient electromagnetic energy could also provide a form of system
backup. 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.
Georgia Tech School of Electrical and Computer Engineering professor Manos Tentzeris displays an inkjet-printed rectifying antenna used to convert microwave energy to DC power. It was printed on flexible material. Georgia Tech Photo: Gary Meek
The researchers are using inkjet technology to print these energy-scavenging
devices on paper or flexible paper-like polymers—a technique they already using
to produce sensors and antennas. The result would be paper-based wireless
sensors that are self-powered, low cost, and able to function independently
To print electrical components and circuits, the Georgia Tech researchers
use a standard-materials inkjet printer. However, they add what Tentzeris calls
“a unique in-house recipe” containing silver nanoparticles and/or
other nanoparticles in an emulsion. This approach enables the team to print not
only radio frequency (RF) components and circuits, but also novel sensing
devices based on such nanomaterials as carbon nanotubes.
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, recalls Rushi Vyas, a graduate student who is working with Tentzeris and
graduate student Vasileios Lakafosis on several projects.
“We can now print circuits that are capable of functioning at up to 15
GHz—60 GHz if we print on a polymer,” Vyas says. “So we have seen a
frequency operation improvement of two orders of magnitude.”
The researchers believe that self-powered, wireless paper-based sensors will
soon be widely available at very low cost.