Published on July 9th, 2011 | by Alexis Argent0
Powering Wireless Devices Over The Air
Ambient electromagnetic energy harvested as power source
Wireless devices are great except for one thing: batteries. Your laptop, phone, travel router, you name it – they all have batteries which require frequently cabling up to a power source for charging. Maybe you were one of those who got excited to see the iPad lasting a whole 12 hours on one charge. What about 12 months, or years – and why can’t we go truly wireless and do away with batteries altogether?
Besides the possibilities of solar power, research projects are also underway proving that it’s possible to harness power from the wireless transmissions we already have and feed that back into our gadgets. The technical challenges are significant, of course, but I think its safe to say that our grandkids will someday be laughing about the idea of batteries the way we laugh about telegraph machines.
Researchers at Georgia Tech have found a way to capture and harness ambient energy transmitted by such sources as radio and television transmitters, cell phone networks, and satellite communications systems. It is believed that 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,” Manos Tentzeris, a professor in the Georgia Tech School of Electrical and Computer Engineering who is leading the research, said in a statement. “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.”
According to the university, the team’s scavenging devices can capture energy transmitted by communications devices, convert it from AC to DC, and then store it in capacitors and batteries. The scavenging technology currently can take advantage of frequencies from FM radio to radar, a range spanning 100 MHz to 15 GHz or higher.
Scavenging experiments utilizing TV bands have yielded power amounting to hundreds of microwatts, and multi-band systems are expected to generate one milliwatt or more, the school reported. The school added that that amount of power is enough to operate many small electronic devices, including a variety of sensors and microprocessors.
The researchers expect that by combining energy scavenging technology with supercapacitors and cycled operation the technology will be able to power devices requiring more than 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 said they 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.
Tentzeris noted that exploiting a range of electromagnetic bands increases the dependability of energy scavenging devices because if one frequency range fades temporarily due to usage variations, the system can still exploit other frequencies. The researchers further noted that the scavenging device could be used by itself or in tandem with other generating technologies or could provide a form of system backup. For example, 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 printers supplied with silver nanoparticles and/or other nanoparticles in an emulsion to combine sensors, antennas, and energy scavenging capabilities on paper or flexible polymers. This approach allows the team to print not only 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, recalled Rushi Vyas, a Georgia Tech graduate student working on the project. “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 in the statement. “So we have seen a frequency operation improvement of two orders of magnitude.” The researchers said that the resulting self-powered wireless sensors could be used for chemical, biological, heat, and stress sensing for defense and industry; RFID (radio frequency identification) tagging for manufacturing and shipping, and monitoring tasks in many fields including communications and power usage. The researchers believe that these self-powered, wireless paper-based sensors will soon be widely available at very low cost.