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Duke Univ. Device Converts Stray Wireless Energy Into Electricity For Charging 216

Posted by Soulskill
from the harvesting-the-ether dept.
Lucas123 writes "Engineers at Duke University say they've constructed a device that can collect stray wireless signals and convert them into energy to charge batteries in devices such as cell phones and tablets. The WiFi collection device, made of cheap copper coils and fiberglass, can even aggregate energy from satellite signals and sound waves (abstract). The researchers created a series of five fiberglass and copper energy conductors on a circuit board, which was able to convert microwaves into 7.3V of electrical energy. By comparison, Universal Serial Bus (USB) chargers for small electronic devices provide about 5V of power. The device, the researchers say, is as efficient as solar cells with an energy conversion rate of 37%."
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Duke Univ. Device Converts Stray Wireless Energy Into Electricity For Charging

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  • Units! (Score:5, Funny)

    by olsmeister (1488789) on Friday November 08, 2013 @04:54PM (#45372191)
    7.3V of energy? USB provides 5V of power? Arggh. I think my head just asploded.
    • Too bad (Score:5, Funny)

      by XanC (644172) on Friday November 08, 2013 @04:57PM (#45372219)

      This summary had such potential, too.

      • by gigne (990887)

        Having just read the "article", the units in the summary are a copy-pasta from the article.

        • by gigne (990887)

          ooohhh... I was way too slow on this. I just chraged in with a sensible reply. /self-whoosh

        • by msauve (701917)
          Which only means that the Duke Pratt School of Engineering has just discredited itself. Maybe they should work on making orgone accumulators, instead.
          • by dbIII (701233)
            It's become popular to appoint vacuous people as press officers to "make science exciting!" in imitation of various people that do the exciting bit but are not vacuous (The Naked Scientists in the UK, Dr Karl in Australia etc). Thus we got stupid announcements like the MIT one molecule thin bulletproof superhero suit (they mixed up lightweight with far too thin to work the way it does) and somebody at Duke Pratt that throws in an alphabet soup of electrical units without having a clue what they mean. It's
            • by msauve (701917)
              How hard is it to then run the PR back through qualified editors for final review? That they don't is another strike against.
      • Re:Too bad (Score:5, Informative)

        by TooTechy (191509) on Friday November 08, 2013 @04:59PM (#45372239)

        Ugh. And the unit we want is missing...

        Look at Watt they make you give... (Clive Owen)

        • by belphegore (66832)

          It's not totally missing. Max legal wifi xmit power is 100mW at the source. Conversion at the receiver is ~37% efficient. So if you're directly on top of the xmitter, capturing ALL the (generally omni-radiated) energy, you'd get 37mW of power. USB on newer devices is like ~10W.

          And of course if you're not capturing 100% of the signal in all directions, and if you're away from the source (remember friends: inverse square power dropoff), then you'll be lucky to get even a mW.

      • Re:Too bad (Score:5, Funny)

        by Mr D from 63 (3395377) on Friday November 08, 2013 @04:59PM (#45372241)
        I am resisting the urge to laugh.
        • Re:Too bad (Score:5, Funny)

          by Billy the Mountain (225541) on Friday November 08, 2013 @05:11PM (#45372385) Journal
          Ohm my god!
          • Re: (Score:2, Funny)

            by Rich0 (548339)

            Seriously, I'm dyne-ing here. Joule have to come up with a better joke next time.

        • Re:Too bad (Score:4, Informative)

          by AmiMoJo (196126) * <mojoNO@SPAMworld3.net> on Saturday November 09, 2013 @07:51AM (#45376373) Homepage

          I'm resisting the urge to cry. TFA on the Duke University web site makes the same mistake.

          The whole article smells of bullshit. It's easy to generate 7V from radio waves, I have done it myself, but the amount of current is tiny. I could run a small LCD clock or ultra low power microcontroller, but never charge a phone from it. Even an old Nokia dumbphone needs far more power than this or the small solar panel it is compared to can provide. We are in battery backed solar calculator territory here.

          It's s shame because there are genuine uses for this kind of technology. Sensors that need to operate in the dark but are very low power, for example. No-one will be charging their smartphone this way unless they get in the order of 100,000x more efficient though.

      • Re:Too bad (Score:4, Funny)

        by Arancaytar (966377) <arancaytar.ilyaran@gmail.com> on Friday November 08, 2013 @05:13PM (#45372407) Homepage

        At least this headline is current.

    • Re:Units! (Score:5, Funny)

      by GenieGenieGenie (942725) on Friday November 08, 2013 @05:01PM (#45372271)
      If you smoke enough pot, as the authors of this cheap attempt at attention-grabbing surely must have, you start seeing double and 5V turns to 55W...
    • 7.3V of energy? USB provides 5V of power? Arggh. I think my head just asploded.

      It's a chain reaction! Now my head asploded with 7.32 Volts of energy and 10 coulombs of mass.
      They could be dealing in metric electrons.

    • Re:Units! (Score:4, Funny)

      by istartedi (132515) on Friday November 08, 2013 @05:03PM (#45372299) Journal

      Just relax and drink a few amperes of beer. That'll help.

    • Re:Units! (Score:5, Funny)

      by wjr (157747) on Friday November 08, 2013 @05:05PM (#45372323)

      And if I scuff my feet while walking across the room, I can generate TWENTY! THOUSAND! VOLTS! OF! ENERGY! Someone hook me up to the power grid!

      • If you say so.

        ZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZ...............poof!

        crackle crackle crackle

        hisssssssssssssss.....

      • by mattack2 (1165421)

        I can't find the exact comic, and googling shows that the joke is an old one.. but one of the major comic strips in the past few weeks talked about a "static electricity car" where you rub your feet on the carpet when the battery starts to wear down.

    • Now if only we knew the conversion coefficient between volts of energy and volts of power, we'd be able to compare the two numbers! Alas, I don't know it. And I'm not going to look for it, that would probably take too many volts of time.
    • by WillKemp (1338605)

      Well, the work was supported by a "Multidisciplinary University Research Initiative from the Army Research Office" and, as they say, military intelligence is a contradiction in terms.

    • by dfsmith (960400)
      My cat can easily produce 5000V of "energy", so this is only 0.14% of stroking a cat. Hmm.
  • by Princeofcups (150855) <john@princeofcups.com> on Friday November 08, 2013 @05:00PM (#45372261) Homepage

    Free energy from the ether! Not.

    • by timeOday (582209)
      Actually reducing waste is the closest you can get to getting something for nothing. When you turn on a lightbulb, what percent of the photons emitted happen to bounce around and eventually fall through the lens on somebody's eye? Hardly any - it's a minuscule percent. Thus "solar"-powered wallpaper to re-absorb energy from lightbulbs sounds stupid but makes perfect sense, if it could be produced cheaply enough. Broadcast RF signals are similar.

      And by the way, if you want to make a display that uses h

      • Thus "solar"-powered wallpaper to re-absorb energy from lightbulbs sounds stupid but makes perfect sense, if it could be produced cheaply enough.

        Not everyone wants to wallpaper the interior of their house in black. All that "wasted" light reflecting off the wallpaper is what allows you to see the walls.

        • by dbIII (701233)
          To continue on that analogy, the spectrum of light emmited is not continuous so you don't have to have black to get most or all of it. With solar radiation it's the same deal and something not that far off a terracotta colour gets almost as much as black.
  • Resistor (Score:5, Funny)

    by Anonymous Coward on Friday November 08, 2013 @05:04PM (#45372311)

    Hey, I can get -174 dBm/Hz from a 50 Ohm resistor too. Free energy!

  • by swschrad (312009) on Friday November 08, 2013 @05:04PM (#45372313) Homepage Journal

    news flash: any antenna provides voltage. usually in the microvolt range. to get enough voltage like they did, say, enough to blow a FET in the front end of a receiver at basically no current, you have to put the antenna in one hell of a strong RF field. a field strong enough to produce enough current to charge batteries or operate CMOS circuits is a field too strong to stay in, according to FCC emission guidelines. so I see this as a project for a grade, and not a "discovery."

    • by sfm (195458)

      Forget Wireless or Satellite signals, they are orders of magnitude less power than you can realistically use. You would do be much better off pointing your antenna at that 100KW FM transmitter up on the hill.

    • by rubycodez (864176)

      People have grabbed enough power out of the air to power their house, living near power lines and using hidden inductor.

      Electromagnetic waves induce current in conductors, and bear eat fish and shits fishy shit in the woods! Story at 10!

  • 7.3V? Psh! (Score:3, Insightful)

    by Schrockwell (867776) on Friday November 08, 2013 @05:10PM (#45372361)
    I can build up a couple kilovolts by scuffing my shoes on the carpet.

    Also, sure it might be 37% efficient, but do you realize how SMALL the density of RF energy is? The Friis transmission equation [wikipedia.org] gives you some idea: it decreases by the square of the distance away from the source, due to that power spreading out in a sphere. When you start off with only a couple mW of power and an omnidirectional antenna, there isn't much power left to harvest when these tiny receiving "metamaterial" antennas are even just a few feet from an access point.
  • by Animats (122034) on Friday November 08, 2013 @05:10PM (#45372363) Homepage

    Here's the actual paper's paywall. [aip.org] All the paper claims is that "A maximum of 36.8% of the incident power from a 900âMHz signal is experimentally rectified by an array of metamaterial unit cells." So they built a rectenna with a waveguide.

    Rectennas [wikipedia.org] have been around for decades, and 82% efficiency [ieee.org] (DC watts out / microwave watts into antenna) has been achieved. So 37% is nothing to be excited about.

    If you hook up two long wires or plates to a diode, any RF in the vicinity will produce some DC across the diode. This is the principle behind "crystal radios". The problem is that you need big antennas to get much power from ambient RF.

    • by hubie (108345) on Friday November 08, 2013 @06:00PM (#45372875)

      Actually, the difference here is that they built a rectenna out of metamaterials, specifically a split-ring resonator (SRR) design. I presume their point here is that they came up with a compact rectenna design that can work fairly well at 900 MHz. The paper you referenced with the 82% efficiency used a dipole antenna for 5.8 GHz. The wavelength at 5.8 GHz is something like 50 mm, and they used a 1/2 wave dipole antenna (their length was around 25 mm). The wavelength at 900 MHz is 333 mm, but their SRR design was only 40 mm on a side (a 1/2 wave dipole would have to be 150 mm or so).

      I don't think they were making any claims of new physics here, but probably pointing out a design that would be fairly compact and leverage all the 900 MHz EMI flying around. For what its worth, their max efficiency occurred for a resistive load of 70 Ohms, which is a reasonable load for something that you want to power with an energy harvester.

      • by Animats (122034)

        The wavelength at 900 MHz is 333 mm, but their SRR design was only 40 mm on a side (a 1/2 wave dipole would have to be 150 mm or so).

        Their waveguide/horn [duke.edu] is much bigger than 40mm. More like 150mm x 500mm or so. It looks like a reasonable sized horn for 900MHz. They've been able to reduce the size of the rectenna at the focus, but the whole assembly is still big.

        Microwave antenna design is weird. Here's some readable background material [w1ghz.org] if anyone cares. Radio hams are routinely able to build 50% efficient microwave antennas. Above that level it starts to get complicated.

  • by k31bang (672440)

    How many amps are we talking about?

  • by Optimal Cynic (2886377) on Friday November 08, 2013 @05:17PM (#45372451)
    This is why idiotic grad student posters shouldn't be shown to over enthusiastic marketing types.
  • Cell phones? (Score:5, Interesting)

    by Okian Warrior (537106) on Friday November 08, 2013 @05:21PM (#45372467) Homepage Journal

    The FCC limits wireless access point RF power to 1 watt.

    From the image, I would guess that the metal thingy is 2 feet square, or about 1/3 square meter. I can't tell from the image whether the capture aperture is the profile or the end of the wedge, but let's give it the benefit of the doubt.

    Standing 10 meters from a WAP is a sphere with area 4*M_PI*R^2 = 1256 m^2. A 1/3 meter capture aperture would eclipse 0.3/1256 of this, for about 240 microwatts. At 37% efficiency, that's about 80 microwatts. (Am I doing this right?)

    Maybe possibly this could power micropower sensors (note: with a 2-foot square antenna on each one).

    But a cell phone?

    • by hubie (108345)
      What you are looking at in the picture is the waveguide they used to test it. The antenna itself is inside the waveguide and is a split ring resonator, 40 mm on a side.
      • by tftp (111690)

        What you are looking at in the picture is the waveguide they used to test it. The antenna itself is inside the waveguide

        The antenna, in this case, is the open end of the waveguide that interfaces with the external EM field. For example, a horn can have a larger aperture, but at the end of it there is only a small probe. It would be incorrect to call the probe "the antenna."

        Or you can say it in a different way. An antenna here is anything that cannot be thrown out without hurting the performance. For ex

    • The FCC limits wireless access point RF power to 1 watt.

      Maybe possibly this could power micropower sensors (note: with a 2-foot square antenna on each one).

      But a cell phone?

      The answer is obvious. More access points.

  • if they can modify this a little bit to absorb nuclear radiation, cosmic rays or universal radiation then they may have invented one of the greatest energy technologies since the solar panel.

    - being able to clean up nuclear radiation would be great to avoid a "permanent" wasteland. then again, it brings the option of using nukes back on the table.
    - absorbing cosmic rays could make space travel safer and possibly satellites lighter.
    - if you can absorb universal radiation then you have a solar panel that alw

    • Re:radiation too? (Score:4, Insightful)

      by Entropius (188861) on Friday November 08, 2013 @05:59PM (#45372867)

      Nuclear radiation doesn't work that way. We have gizmos that turn nuclear radiation into power; they're called radiothermal generators, and work by absorbing the radiation with some material that heats up, then capturing the thermal energy as it flows across a Peltier junction. We power spacecraft with 'em.

      But this doesn't make the plutonium less radioactive any faster. Those plutonium nuclei are still going to take their sweet time decaying.

      Nuclear power plants take advantage of this, too; heat in the reactor core is heat in the reactor core, and it doesn't matter whether it comes from fission directly or from secondary decay of fission products. But we can't do anything magic to fission products to make them decay into something stable any faster; eventually they get far enough down the decay chain to something long-lived enough that it's not worth trying to harvest the heat they release any more.

      • by Carnildo (712617)

        But we can't do anything magic to fission products to make them decay into something stable any faster

        Actually, we can. Neutron bombardment will usually create particles that are less stable, so they take a faster decay chain down to a stable state. It's a tradeoff: your radioactive waste becomes more radioactive, but for less time.

    • by rubycodez (864176)

      Absorbing nuclear radiation and making electricity is a done deal, see your local nuclear power plant or talk to RPG generator manufacturer for a couple different methods.

      Cosmic ray to electricity is pretty trivial too, what with a cosmic ray being a charged particle (usually proton) and all....

    • by fluffy99 (870997)

      - being able to clean up nuclear radiation would be great to avoid a "permanent" wasteland. then again, it brings the option of using nukes back on the table.

      Crap my tablet isn't working! Quick get the US to go nuke some pissant country so I can get youtube to show me cute kittens again. Oh wait, aren't we already bombing 2nd-world countries to maintain our flow of cheap oil?

    • If the early nuclear reactors were not built with the dual role of creating bombs in mind, then there would be no wasteland. Pebble bed reactors are one example of clean, failsafe nuclear power. The basic principle in TFA has been know for centuries, I learnt it the 60's as child when dad helped me build a crystal radio. The material with the properties you describe is also well known to electrical engineers, they call it "unobtanium".
  • by mwehle (2491950) on Friday November 08, 2013 @05:24PM (#45372511) Homepage

    Engineers at Duke University say they've constructed a device that can collect stray wireless signals

    WTF is a "stray wireless signal"? This is a signal without an owner? Slipped out of its collar?

  • Those "stray wireless signals" may well be doing something useful.
  • Looks to me like a simple Yagi antenna inside of a waveguide. Inside a waveguide, and for an optimum tuned Yagi, the signal would have to be directionally pointed at this setup. Its not like you are going to snag some arbitrary signal that isn't pointed in your general direction. Perhaps if you are eating lunch on a picnic table while standing in front of a microwave repeater, you might be able to charge your cell phone. But then you needed to carry this rig with you while the extra battery option would cle
    • by tftp (111690)

      A Yagi will not work inside of a waveguide for a million reasons, starting with the fact that there is no flat wavefront to speak of. Yagi antenna works on the principle that individual elements are hit with the flat wave at a slightly different time, which translates to a phase shift at a given frequency. If you build the antenna just right, these phase shifts are mutually neutralized, but only if the wave comes from there, and on a certain the frequency. Then the signals from multiple elements can be com

  • by foxalopex (522681) on Friday November 08, 2013 @05:59PM (#45372863)

    This doesn't even pass the common sense logic rules if you understand physics. The issue is there's not much energy in these types of radio waves. A cellphone transmits a maximum of around 1 watts, a wifi router 50 milliwatts if you're lucky. By the time the radio waves have reached you their effective power has already dissipated by the square of the distance. Sure you might get a voltage potential that's in the 7 volt range but how's that useful if there's next to no current to do anything. Short of standing under a high voltage power line or next to some high power transmitter which probably wouldn't be safe for your health, this isn't going to work.

    People also misunderstand Tesla's work. Tesla's work wasn't that you could just pop up an antenna and get free power. His plans involved putting up a massive transmission tower that would dump power into the air at an efficient frequency. A coil and antenna could then be used to pick up this power wirelessly. Great idea but the issue then is how exactly would you charge for this power when anyone with some know how could build a receiver to grab the "free" power?

    • by Animats (122034)

      Tesla's work wasn't that you could just pop up an antenna and get free power. His plans involved putting up a massive transmission tower that would dump power into the air at an efficient frequency. A coil and antenna could then be used to pick up this power wirelessly.

      Right. When you read his plans, he's taking about a system where a small town is powered by a massive transmitter, each attic is full of antennas, and each house gets one (1) 40-watt light bulb.

    • Well, even if you have very low current you can just charge your phone over a longer time period. Say, a few decades. It would be perfect for people waiting at a DMV, for example!
    • by Dan East (318230)

      Great idea but the issue then is how exactly would you charge for this power when anyone with some know how could build a receiver to grab the "free" power?

      Doesn't seem to stop them from collecting money in the UK for essentially the same thing: https://en.wikipedia.org/wiki/Television_licensing_in_the_United_Kingdom [wikipedia.org]

    • by Kaenneth (82978)

      Great idea but the issue then is how exactly would you charge for this power when anyone with some know how could build a receiver to grab the "free" power?

      Just encrypt the signal.

  • We stuck a small TV transformer on the local power companies street level distribution transformer..

  • This feels like we're cleaning the crap out of the air :-) But I already see a way to boost sales: Avoid having to wear tin-foil hats, clean the mind-control signals out of the air before they even reach you!

    -Matt

  • At least it seems that >90% of slashdot readers recognized immediately just how stupid the original article was.

    Also, these were STUDENTS. Its actually a nice student project to try to make a RF power receiver. Its quite possible that the students DID use the right units and the person doing the press release didn't understand. (and is currently being crucified by his / her management).

    One could even imagine applications for micro-power devices used in an environment where there is some RF background bu

    • by dbIII (701233)

      NSA bugs embedded in building materials for example

      The guy who invented the theremin apparently made passive bugs like that in the 1940s (http://en.wikipedia.org/wiki/Thing_%28listening_device%29).

  • Could be they are cutting down on some peoples signal strength.

  • by Ungrounded Lightning (62228) on Friday November 08, 2013 @09:52PM (#45374499) Journal

    This device will also interfere with the radio signals. It will both attenuate them and create harmonics due to the rectifiers.

    "Raising ground resistance" by having radio-energy-utilizing devices pull power from the air is a non-trivial issue.

    Example: A former colleague had, previously, been a plant manager for a factory in a small African country. The plant was in the country's capital, home to their "voice of the fearless leader" high-powered radio station.

    One day, while touring the plant, he found a collection of burned-out fluorescent tubes, and had them hauled away. Shortly after he was contacted by his maintenance head, who asked him not to do it again. It seems there was a black market in burned out fluorescent tubes.

    The radio station was so strong that, if you put three feet of wire on each end of a burned-out tube it would light up quite nicely from the radio power. A lot of people couldn't afford electricity and light fixtures. But a burned out tube and six feet of wire was readily available. So much of the town's houses were illuminated this way.

    So many were, in fact, that the radio signal would no longer reach the edges of the country. So Fearless Leader would send his troops through town when the attenuation got to be a problem, and they'd confiscate and smash the tubes of all the improvised radio-powered lights they found. After each such raid, the people would be down at the plant to buy more "dead" tubes, creating a profitable side-business for the maintenance guy.

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