Device scavenges power out of thin air

GEORIGIA TECH (US) — A new way to capture and harness energy from the air could lead to paper-based wireless sensors that are self-powered, low-cost, and able to function independently almost anywhere.

“There is a large amount of electromagnetic energy all around us, but nobody has been able to tap into it,” says Manos Tentzeris, professor of electrical and computer engineering at Georgia Institute of Technology (Georgia Tech).

“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 capability.”

Inkjet printers are used to combine sensors, antennas, and energy-grabbing capabilities on paper or flexible polymers. The resulting self-powered wireless sensors may 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 a variety of fields including communications and power usage.

Communications devices transmit energy in many different frequency ranges, or bands.  The team’s scavenging devices are able to capture the energy, convert it from AC to DC, and then store it in capacitors and batteries. The scavenging technology can presently take advantage of frequencies from FM radio to radar, a range spanning 100 megahertz (MHz) to 15 gigahertz (GHz) or higher.

Experiments utilizing TV bands have already yielded power amounting to hundreds of microwatts. Multi-band systems are expected to generate one milliwatt or more—enough power to operate many small electronic devices, including a variety of sensors and microprocessors.

By combining energy-scavenging technology with super-capacitors and cycled operation, researchers expect to be able 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 reached.

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

Exploiting a range of electromagnetic bands increases the dependability of energy-scavenging devices, Tentzeris says. 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.

Utilizing 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.

The researchers are using inkjet technology to print the energy scavenging devices on paper or flexible paper-like polymers—a technique they are already using to produce sensors and antennas.

To print electrical components and circuits, researchers use a standard materials inkjet printer, but add what Tentzeris calls “a unique in-house recipe” containing silver nanoparticles and/or other nanoparticles in an emulsion, allowing researchers to print not only RF components and circuits, but also novel sensing devices based on such nanomaterials as carbon nanotubes.

When Tentzeris began inkjet printing of antennas in 2006, the paper-based circuits only functioned at frequencies of 100 or 200 MHz, says graduate student Rushi Vyas.

“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, resulting in a proliferation of autonomous, inexpensive sensors that 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 material.
  • 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 condition.
  • 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 problems.
  • Wearable bio-monitoring devices: This emerging wireless technology could become widely used for autonomous observation of patient medical issues.

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