Ambient Energy Harnessed for Small Electronic Devices
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
“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. “We are using an
ultra-wideband antenna that lets us exploit a variety of signals in
different frequency ranges, giving us greatly increased power-gathering
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 given at the IEEE Antennas
and Propagation Symposium in Spokane, Wash. The discovery is based on
research supported by multiple sponsors, including the National Science
Foundation, the Federal Highway Administration and Japan’s New Energy
and Industrial Technology Development Organization (NEDO).
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
Scavenging experiments utilizing 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 supercapacitors and cycled operation, the
Georgia Tech team expects to power devices requiring above 50
milliwatts. In this approach, energy builds up in a battery-like
supercapacitor and is utilized when the required power level is
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 the air.
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. If
one frequency range fades temporarily due to usage variations, the
system can still exploit other frequencies.
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.
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.
researchers are utilizing 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 almost anywhere.
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 RF components and circuits, but also novel sensing
devices based on such nanomaterials as carbon nanotubes.
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.
“We can now print circuits that are capable of functioning at up
to 15 GHz -- 60 GHz if we print on a polymer,” Vyas said. “So we have
seen a frequency operation improvement of two orders of magnitude.”
researchers believe that self powered, wireless paper-based sensors
will soon be widely available at very low cost. The resulting
proliferation of autonomous, inexpensive sensors could be used for
applications that include:
• Airport security: Airports have both
multiple security concerns and vast amounts of available ambient energy
from radar and communications sources. These dual factors make them a
natural environment for large numbers of wireless sensors capable of
detecting potential threats such as explosives or smuggled nuclear
• Energy savings: Self powered wireless sensing
devices placed throughout a home could provide continuous monitoring of
temperature and humidity conditions, leading to highly significant
savings on heating and air-conditioning costs. And unlike many of
today’s sensing devices, environmentally friendly paper-based sensors
would degrade quickly in landfills.
• Structural integrity: Paper
or polymer-based sensors could be placed throughout various types of
structures to monitor stress. Self powered sensors on buildings,
bridges or aircraft could quietly watch for problems, perhaps for many
years, and then transmit a signal when they detected an unusual
• Food and perishable material storage and quality
monitoring: Inexpensive sensors on foods could scan for chemicals that
indicate spoilage and send out an early warning if they encountered
• Wearable bio-monitoring devices: This emerging
wireless technology could become widely used for autonomous observation
of patient medical issues.