Electromagnetic Harvester claims to charge batteries with ambient energy
by Jonathan Fincher / February 8, 2013
We’re surrounded by electromagnetic fields almost everywhere these days. Just because they’re almost imperceptible doesn’t mean they can’t be used as a source of energy though. One student in Germany recently built the Electromagnetic Harvester, a small box that allegedly charges an AA battery using just the electromagnetic fields given off by the likes of power lines, vehicles and electronic gadgets. Dennis Siegel, a digital media student at the University of the Arts in Bremen, designed the handheld charger as a way to recover some of the energy from these electromagnetic fields. It may sound a little sketchy, but it’s an idea that many researchers, including a team at Georgia Tech, have been exploring for years. The main issue with this form of energy collection is the amount of power it generates tends to be incredibly small, which might explain why it takes a full day for the Electromagnetic Harvester to charge a single AA battery.
According to Siegel, using the harvester involves simply holding it up to anything with an electromagnetic field – a cell phone, a coffee maker, a commuter train, etc. Once it enters a strong enough field, a red LED will light up to indicate it is charging. It also has a magnet on the back to leave it attached near an EMF source and can charge from the combined fields of living things, like when a person pets a dog. Seigel designed two different versions of the harvester: one for frequencies below 100Hz (like those found in electricity mains) and one for frequencies above 100Hz (like those found in Bluetooth, WLAN, and radio broadcasts). But don’t start thinking this signals the end of charging devices through ordinary wall sockets just yet. While the potential for this type of technology being used to charge very low-powered devices like wireless sensors or RFID tags is there, we remain very skeptical about any practical consumer electronics applications. Aside from not being able to generate enough power for a typical smartphone user, Siegel has yet to reveal any specifics on how his take on the ambient energy charging device works – only that it involves “coils and high frequency diodes.”
German student creates electromagnetic harvester that gathers free electricity from thin air
by Sebastian Anthony / February 12, 2013
A German student has built an electromagnetic harvester that recharges an AA battery by soaking up ambient, environmental radiation. These harvesters can gather free electricity from just about anything, including overhead power lines, coffee machines, refrigerators, or even the emissions from your WiFi router or smartphone. This might sound a bit like hocus-pocus pseudoscience, but the underlying science is actually surprisingly sound. We are, after all, just talking about wireless power transfer — just like the smartphones that are starting to ship with wireless charging tech, and the accompanying charging pads. Dennis Siegel, of the University of Arts Bremen, does away with the charging pad, but the underlying tech is fundamentally the same. We don’t have the exact details — either because he doesn’t know (he may have worked with an electrical engineer), or because he wants to patent the idea first — but his basic description of “coils and high frequency diodes” tallies with how wireless power transfer works. In essence, every electrical device gives off electromagnetic radiation — and if that radiation passes across a coil of wire, an electrical current is produced. Siegel says he has produced two versions of the harvester: One for very low frequencies, such as the 50/60Hz signals from mains power — and another for megahertz (radio, GSM) and gigahertz (Bluetooth/WiFi) radiation.
The efficiency of wireless charging, however, strongly depends on the range and orientation of the transmitter, and how well the coil is tuned to the transmitter’s frequency. In Siegel’s case, “depending on the strength of the electromagnetic field,” his electromagnetic harvester can recharge one AA battery per day. He doesn’t specify, but presumably one-AA-per-day is when he’s sitting next to a huge power substation. It makes you wonder how long it would take to charge an AA battery via your coffee machine, or by leeching from your friend’s mobile phone call. As a concept, though, Siegel’s electromagnetic harvester is very interesting. On its own, a single harvester might not be all that interesting — but what if you stuck a bunch of them, magnetically, to various devices all around your house? Or, perhaps more importantly, why not use these harvesters to power tiny devices that don’t require a lot of energy? Sensors, hearing aids (cochlear implants), smart devices around your home — they could all be powered by harvesting small amounts of energy from the environment. One question does remain, though: How much ambient, wasted electromagnetic radiation is actually available? There are urban legends about people who install coils of wire in their garage, and then suck up large amounts of power from nearby power substations or radio transmitters. Would the power/radio company notice? Would it degrade the service for other people?
“The omnipresence of electromagnetic fields is implied just by simple current flow. We are surrounded by electromagnetic fields which we are producing for information transfer or as a byproduct. Many of those fields are very capacitive and can be harvested with coils and high frequency diodes. Accordingly, I built special harvesting devices that are able to tap into several electromagnetic fields to exploit them. The energy is stored in an usual battery. So you can for example gain redundant energy from the power supply of a coffee machine, a cell phone or an overhead wire by holding the harvester directly into the electromagnetic field whose strength is indicated by a LED on the top of the harvester. Depending on the strength of the electromagnetic field it is possible to charge a small battery within one day. The system is meant to be an option for granting access to already existing but unheeded energy sources. There are two types of harvester for different electromagnetic fields: a smaller harvester that is suitable for lower frequencies below 100Hz which you can find in the general mains (50/60Hz, 16,7Hz) and a bigger one that is suitable for lower and higher frequencies like radio broadcast (~100MHz), GSM (900/1800MHz) up to Bluetooth and WLAN (2,4GHz).”
How wireless charging works
by John Hewitt / October 15, 2012
The fact that over 200,000 people have downloaded one of the various “shake to charge” apps, now available from Google Play, indicates our willingness to suspend any form of practical reasoning in pursuit of the dream of wireless charging. A quick investigation of the source code would likely reveal these apps do little more than to link the interrupt signal from the accelerometer to a progress bar indicating an alleged battery charge. A piezoelectric accelerometer could generate a small voltage secondary to deformations induced by rapid motions applied to it, however trying to use that millivolt signal to charge a battery would not be practical. In order words, shaking your smartphone isn’t going to do anything but get your arm tired.
During any energy conversion there will be losses in going from one form to another. The magnitude of those losses is what dictates the practicality of any type of wireless charging. Magnetic or inductive charging, in particular has been effectively used for some time to power various kinds of biomedical implants. Presently it is the safest and most enduring method to accomplish the job of transferring power to the inside of the body. In these systems, oscillating current in an external coil of wire generates a changing magnetic field which induces a voltage inside an implanted coil. The current resultant from this voltage can charge a battery or power the device directly. While a moving magnet might just as well be used to externally generate the field, an external coil is simply more practical. Apple has just filed a patent for hardware which could make the shake to charge concept a reality, at least in theory. They claim a unique design incorporating internal moveable magnets, and a flat printed circuit board coil. Current chip efficiencies will however preclude practical implementation of this scheme for some time.
Many smartphone users will be wondering wonder whether their near field communication (NFC) chip can be used to harvest power from a dedicated external source, or perhaps an ambient electromagnetic source like WiFi. In theory it is possible and such systems are on the market already, however not every NFC chip would be up to the task. To achieve maximum efficiency the system should be optimized for a use at a particular separation distance, angle of incidence, phase, and frequency such that it is in a resonant condition. Resonance in an electromagnetic system can be likened to pushing a child on swing only when the swing is at the high point. Anywhere else and the energy transferred to the child will be reduced. If the separation distance is no more than a quarter of the wavelength, such a system can operate at efficiencies up to 35%.
One thing to keep in mind when considering wireless charging: If your charging system is throwing away nearly all of the 10 or so amps available from your wall outlet just to provide you with convenient at-a-distance charging, not only will charging be wasteful but it will be slow. Other wireless charging technologies relying on ultrasound or solar power are being developed, for example by Ubeam. For the time being, however, magnetic inductive charging technologies — spearheaded by the Qi consortium and smartphones like the Nokia Lumia 920 — such have taken the stage.
SCAVENGING AMBIENT ENERGY
Scavenging ambient electromagnetic energy to power small electronic devices
by Darren Quick / July 8, 2011
As you sit there reading this story you’re surrounded by electromagnetic energy transmitted from sources such as radio and television transmitters, mobile phone networks and satellite communications systems. Researchers from the Georgia Institute of Technology have created a device that is able to scavenge this ambient energy so it can be used to power small electronic devices such as networks of wireless sensors, microprocessors and communications chips. Manos Tentzeris, a professor in the Georgia Tech School of Electrical and Computer Engineering, and his team used inkjet printing technology to combine sensors, antennas and energy scavenging capabilities on paper or flexible polymers. Presently, the team’s scavenging technology can take advantage of frequencies from FM radio to radar, a range of 100 Mhz to 15 GHz or higher. The devices capture this energy, convert it from AC to DC, and then store it in capacitors and batteries. “There is a large amount of electromagnetic energy all around us, but nobody has been able to tap into it,” said Tentzeris. “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.”
So far the team has been able to generate hundreds of milliwatts by harnessing the energy from TV bands. It is expected that multi-band systems would generate one milliwatt or more, which is enough to operate small electronic devices, including a variety of sensors and microprocessors. Tentzeris says exploiting a range of electromagnetic bands increases the dependability of energy scavenging devices as if one frequency range fades due to variations in usage, other frequencies can be used to pick up the slack. The team is also looking at combining the energy scavenging technology with supercapacitors and cycled operation so that the energy builds up in a battery-like superconductor and is utilized once the required level is reached. The team expects this approach would be able to power devices requiring over 50 milliwatts. The researchers have already successfully operated a temperature sensor using electromagnetic energy captured from a television station that was half a kilometer away. They are now preparing another demonstration in which a microprocessor-based microcontroller would be activated simply by holding it in the air.
The researchers say the technology could also be used in tandem with other electricity generating technologies. For example, scavenged energy could assist a solar element to charge a battery during the day and then at night, scavenged energy would continue to increase the battery charge or would prevent discharging. It could also be used as a form of system backup. If a battery failed completely, the scavenged energy device could allow the system to transmit a wireless signal while maintaining critical functions. The Georgia Tech team believe that self-powered, wireless paper-based sensors will soon be widely available at very low cost, making then attractive for a range of applications, such as 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.