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Power Wireless Networking

Is RCA's Airnergy Snake Oil? 271

Posted by kdawson
from the deepness-in-the-sky dept.
Ben Newman writes "Of all the tech that's come out of CES this week, nothing has gotten the blogosphere more excited then the RCA Airnergy. A lot of people love the thought of an ever-recharging cell phone, and the Airnergy promises to constantly charge its internal battery through 2.4GHz wireless signals. Neat idea, but as some commenters have pointed out the energy just isn't there to make this work — BOTECs for a full charge range from 100 days to 32 years. Plus, don't let the RCA brand fool you into thinking this must be from a legitimate company: RCA hasn't existed as anything more then a licensed brand name for a couple of decades. So what do Slashdotters think — real deal or 21st century hokum?"
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Is RCA's Airnergy Snake Oil?

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  • by francium de neobie (590783) on Wednesday January 13, 2010 @02:31AM (#30747934)
    Is totally gonna charge up your battery and run your cell phone for days.

    The inverse square law and dBm being a logarithmic unit can all go to hell.
    • the mythbusters tried to get power from the em radiation from a high voltage line. That doesn't work nothing will.

      • by TheKidWho (705796) on Wednesday January 13, 2010 @02:45AM (#30747984)

        Not necessarily, frequency is just as important as voltage and current.

      • Re: (Score:3, Insightful)

        by amorsen (7485)

        That really should have worked, with a sufficiently long antenna. It'll be induction, but that ought to count too.

      • Re: (Score:2, Interesting)

        by Anonymous Coward

        Much earlier than the mythbusters a german tv-show for kids, the "Sendung mit der Maus" ("program with the mouse") made the point: they held up a neon tube next to a state radio-transmitter and it began to glow. And they explained to the kids, that it will work next to such a high energy radio transmitter, but it is also robbery according to german law. So don't try, kids, unless you don't mind being a thief.

      • by mcgrew (92797) * on Wednesday January 13, 2010 @09:04AM (#30749856) Homepage Journal

        Mythbusters isn't always right. For example, they busted the "myth" of an ancient Greek "Death Ray" by making one that didn't work. Some MIT kids showed it was possible (this was discussed on slashdot last year).

        They had busted the "myth" of a sniper shooting another sniper through the second sniper's scope, and the US Army showed they were wrong, by giving them some better ammo. They covered this on the show itself.

        I saw the episode you refer to, IIRC they used a device they bought from the internet. Just because that device wouldn't work doesn't mean none would. You should be able to get voltage from stray EMF from your house current; a crystal radio has no power source and is powered only by the transmitter's signal. But it takes tiny amounts of current for headphones to work, a phone takes quite a bit of juice.

        So I'm skeptical. I'll believe it when I see one. I do think you could probably make an LCD clock without a power source, you can run an LCD watch from a potato battery.

    • by Fluffeh (1273756)
      While I am certainly no degree holder or scholar in this field, I often wondered about the following:

      A coil of wire with a current running through it emits a magnetic force. From memory, a magnetic force applied to a coil generates a current. Seeing as the earth is covered in a huge magnetic shell, how come people don't actually generate power this way? Is the magnetic field simply too weak compared to what is needed to generate a current of any value?

      Perhaps one of you smart folk here might help me o
      • by Zondar (32904) on Wednesday January 13, 2010 @02:50AM (#30748008)

        It also has to do with a static field vs a moving field. Make a coil of wire, hold a magnet next to it, hook it to a voltmeter. Notice the coil doesn't have any induced voltage until you move the magnet. You can't get any energy out of a static field, no matter the strength of the field.

      • by zmollusc (763634) on Wednesday January 13, 2010 @02:50AM (#30748010)

        I think it is the _change_ in magnetic flux that generates a current in a conductor, not just the presence of magnetism.

        • bingo. it's flux (change in magnetic field), not the magnetic field itself, that produces a current.
      • by KulSeran (1432707) on Wednesday January 13, 2010 @03:13AM (#30748112)

        Nasa HAS tried this.
        http://en.wikipedia.org/wiki/Electrodynamic_tether [wikipedia.org]
        You can generate electricity as you move around the earth. Being in orbit, you are going fast enough to make worthwhile magnetic flux, and you are free of air resistance that would keep you from deploying the tether if you were lower in the atmosphere.

        • trouble is, that earths magnetic field seems to not be as even as we had imagined it, and you tend to get surges that ruin the equipment. (weld the tether reel solid, foul up electronics and my personal favorite, snap the tether like a fuse)
      • by Anonymous Coward on Wednesday January 13, 2010 @03:19AM (#30748140)

        A *changing* magnetic field generates a current. If you just take a coil with some wires attached, and hook up a voltmeter, nothing will happen. Only when you start moving your coil through a magnetic field will you start to see volts. (Earth's field is extremely weak, but with a big coil and a sensitive meter you could see a small current.)

        The reason this can't be used for infinite power generation is that the coil will resist movement. Any flow of current generates a magnetic field of its own, and if you do the math, it turns out that the induced current in your coil creates a field in opposition to the field it's moving through. It works against you like a kind of friction, or like air resistance. If you just give the coil an initial kick, it will quickly run down to a stop. In order to generate power you have to keep putting energy into the system.

        In other words, you're not draining energy from the magnetic field, you're just converting the kinetic energy you put in.

        This is in fact how generators work. A big conductive coil is spun around inside the field of some permanent magnets. If your generator is connected to a water turbine, you're converting the kinetic energy in falling water into the kinetic energy of a spinning coil and thence to electrical energy in a wire.

      • by jo_ham (604554)

        As others have pointed out, you need a change in the field to generate current, either by moving through it or moving the thing making the field. You can observe this effect on a high speed aircraft, where there is a measurable potential difference between the wingtips as it flies though the earth's magnetic field. It's not really strong enough to extract anything useful out of it - you couldn't hook it up to a motor and power the plane, for instance. You'd do better bolting PV panels on every exposed surfa

      • by gweihir (88907)

        A coil of wire with a current running through it emits a magnetic force. From memory, a magnetic force applied to a coil generates a current. Seeing as the earth is covered in a huge magnetic shell, how come people don't actually generate power this way? Is the magnetic field simply too weak compared to what is needed to generate a current of any value?

        Perhaps one of you smart folk here might help me out with this little "backburner" thought that I have had for a while?

        You have something wrong here: Only a

    • by pydev (1683904)

      Well, we can't do much about the inverse square law, but we can easily switch to linear units. :-)

    • I see your point, and you are dead on - today!

      I remember an episode of Star Trek where the Captain and Spock admire a source of lighting that "produces light, but no heat! - How advanced!" yet, compared to incandescent bulbs, that's an apt description of LED lights, especially those designed for high efficiency [wikipedia.org]!

      Let's talk now about Cell Phones - I almost bought a cheapie cell phone for $29 that was about the depth/width/length of a hershey chocolate bar. It sported 2 days of battery life, unlimited text/pic

      • by gweihir (88907) on Wednesday January 13, 2010 @04:19AM (#30748362)

        Now, if you figure that we can improve power conductivity by, oh say, 50%, and can cut power utilization by 100x, (1/10th the amount claimed by Bell Labs) then suddenly, the charge rates from a 150 mw 802.11 radio source 5 meters away actually seems reasonable!

        It won't happen today, or tomorrow. But in a few years? Not only possible, but likely!

        Not at all. Cellphones need something like 100mW...2W RF output to cut though background static and get a signal to the cell tower. And by conservation of energy that means even if nothing at all besides the RF emitter consumes energy, the power consumption will be at least 100mW...2W.

        • by Rysc (136391) *

          But it would work, right? It just wouldn't be enough for an indefinite charge. I think it's enough that you extend unplugged lifetime, surely. It's not necessary to have an everlasting charge so much as a longer-lasting charge, offsetting the energy consumption by continual recharging. Isn't that the idea?

    • Re: (Score:3, Interesting)

      by Gordonjcp (186804)

      I tried it with a 500mW power source on 460MHz using a pair of resonant quarter-wave aerials. At about one metre separation, it was receiving around -6dBm, or about 250uW. So that's ten times the power, ten times closer, on a lower frequency with better propagation. Ten metres away and 50mW would give -26dBm which my meter won't measure, but is one hundredth the power - 2.5uW. Good luck charging a battery with that.

      Gordon MM0YEQ

    • Sure it will recharge your battery...

      over the next few years. :P

    • by mpe (36238)
      Is totally gonna charge up your battery and run your cell phone for days.

      Why not have a phone which works like self winding/powered watches? Something which extracts mechanical energy from body movement. Indeed with a phone such a mechanism could be put entirely inside the "battery" so no need to modify anything else.

      The inverse square law and dBm being a logarithmic unit can all go to hell.

      You might do better by covering the thing in photovoltaic cells. Given that there are likely to be more visible
  • RCA (Score:5, Funny)

    by MindlessAutomata (1282944) on Wednesday January 13, 2010 @02:36AM (#30747950)

    Plus, don't let the RCA brand fool you into thinking this must be from a legitimate company

    Yes, when I am confronted with an RCA TV, the first thing I think is, "a legitimate company produced this."

    • Plus, don't let the RCA brand fool you into thinking this must be from a legitimate company

      Yes, when I am confronted with an RCA TV, the first thing I think is, "a legitimate company produced this."

      Some people are old enough to remember when there was an actual legitimate RCA.

      Now get off my lawn.

      • Re: (Score:3, Funny)

        by ibsteve2u (1184603)
        Sorry about the lawn. I was just admiring the lightbulb in your lamp post; nice to see Americans using products from American companies like Sylvania. Was that a Zenith TV I saw through your window?
      • Re: (Score:3, Informative)

        by mcgrew (92797) *

        And Maytag and Zenith. They're both made in Mexico now.

  • Maybe we just need to remove all the shielding off our microwave ovens and run them on full. That should pollute the immediate vicinity with enough power to charge the devices.

  • by MrEricSir (398214) on Wednesday January 13, 2010 @02:45AM (#30747978) Homepage

    YES

    • You are not considering the possibility that this device is not intended for your average user.
      Maybe it was envisioned with a more... active crowd in mind.

      You know... the kind of people who would find the prospect of running up to one of these [wikipedia.org] a valid possibility.

      Also, it would make a GREAT plausible denial device for the active denial system (PDDfADS).
      Hang one of those around your neck and you can claim that you were just trying to charge your phone (and not the ADS), when you are arrested for whatever act

  • by Tsunamio (465339) on Wednesday January 13, 2010 @03:02AM (#30748062) Homepage

    I'm sure we can look forward to a vigorous debate, where both sides bring up excellent points. I certainly cannot say where the slashdot community will land on this question, and the article certainly doesn't give any hints! Thanks, Ben, for your valuable question, and I hope you find the answers both challenging and enlightening.

    • If there's a debate on whether this technology can work, it goes like this...

      Chuck Norris roundhouse kicked conservation of energy in the nuts, and he charged up his iPhone from his WiFi router's signal in 1 minute, 100 meters away!

      If you're getting -70dBm, and Chuck Norris's iPhone is getting -70dBm, Chuck Norris is getting more power than you!
  • by doishmere (1587181) on Wednesday January 13, 2010 @03:09AM (#30748096)
    Assume a wireless router broadcasts at 1W, uniformly outward. Suppose the charger has an effective surface area of 4" * 2", or about 50cm^2. Assume the charger is 10m away fro the router; then the charger can receive no more than (1W) * (50cm^2) / (4 * pi * 1000cm * 1000cm) = 4 * 10^-6 W. A Blackberry battery on Bestbuy.com claims to store 1100 mAh @ 3.7V of energy, so the device could charge a powered-off Blackberry in (1100 mAh * 3.7V) / (4 * 10^-6 W) = 116 years... I'm wrong, or the device doesn't work as claimed.
    • Re: (Score:2, Funny)

      by doishmere (1587181)
      Of course, I can't be wrong: http://www.xkcd.com/687/ [xkcd.com]
    • by Skal Tura (595728)

      To add to complexity of this, there's multiple devices transmitting all the time.

      So we would need to first observe the average of all broadcasts strengths to do more precise calculation.

      Tho unless, there's about 1,016,160W transmitter within 10meters (enough to charge blackberry in 1hr), according to your maths this device cannot work, unless it's extremely small powered device, consuming about 1/100th of a blackberry and there's over 100W of broadcasting within 10meters, we start to reach the 1hr ballpark.

    • by LMacG (118321) on Wednesday January 13, 2010 @07:33AM (#30749168) Journal

      I notice you switched units in your surface area calculation. Do you, by any chance, work on spacecraft going to Mars?

  • by pydev (1683904) on Wednesday January 13, 2010 @03:21AM (#30748148)

    Obviously, you put this thing in the microwave, set it to High, and let it charge for 30 minutes.

    (Please let it cool down before removing it from the oven.)

  • This is embarrassing. Embarrassing for Thompson, which owns the RCA brand. Embarrassing for press who took it seriously. Serious career trouble for whomever authorized licensing the name to the clowns behind this.

    We'll probably hear some disclaimer from Thompson shortly.

  • Tesla? (Score:5, Funny)

    by MikeFM (12491) on Wednesday January 13, 2010 @03:42AM (#30748224) Homepage Journal
    Tesla seemed to think this idea was workable. Can't say about RCA's product but I'll trust Tesla.
    • by gweihir (88907)

      Tesla seemed to think this idea was workable. Can't say about RCA's product but I'll trust Tesla.

      Oh, it is. If you can live with horrible efficiency, unless very close to the sender. For typical ambient RF, you are lucky to get 1 miliwatt out of this, far less than is usable as a battery charger. This is really basic physics stuff. While the idea is sound, it just does not work with the numbers found in practice.

    • Well two things (Score:4, Insightful)

      by Sycraft-fu (314770) on Wednesday January 13, 2010 @04:48AM (#30748492)

      1) Note that Tesla never got wireless power working. He liked the idea, but he couldn't make it work. Also note that to this day we still don't have it. That should tell you something. The problem, it turns out, is that EM power decays logarithmically with distance. So a little more distance translates to large losses in power. You have a 1 watt transmitter and it is only a few milliwatts when you get a bit away from it. It would be extremely inefficient to transmit power through the air, even ignoring other problems.

      2) Tesla was nuts, like "lock him in a soft room" crazy. He was brilliant, don't get me wrong, but he was also crazy. The guy had some really wacky ideas, along with some extremely genius ones. Just because Tesla thought something would work, doesn't mean it would.

      • Re: (Score:2, Informative)

        by lamare (1349411)

        According to Nasa's "Advanced Energetics for Aeronautical Applications: Volume II" Tesla did get it working:

        http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20050170447_2005172301.pdf [nasa.gov]

        "However, Tesla's claims were backed up with documented experimental demonstrations rather than mathematical equations. In the following quotation, Meyl describes one of Tesla's demonstrations and states that Hertz's technology could not have accomplished such a demonstration:

        In Colorado Springs he had built a 10 kW transmi

    • by argent (18001)

      Tesla blacked out Colorado Springs trying to get enough power into the air to make broadcast power work. He thought aliens were talking to him. He was a genius, but he was also missing a few screws.

  • back to basics (Score:5, Insightful)

    by vacarul (1624873) on Wednesday January 13, 2010 @03:48AM (#30748244)
    I'll get more energy with a hand-crank generator...
    • by MobileTatsu-NJG (946591) on Wednesday January 13, 2010 @05:43AM (#30748696)

      I'll get more energy with a hand-crank generator...

      ... depending on which picture is in front of you.

    • I think the question is if you carry one with you.

      If this technology worked properly instead of most people here assuming that it doesn't it would be huge. The idea of having a few wireless units plugged into home outlets like a Glade air freshener and never having to deal with this charger for this unit and another for another unit and tracking down yet another charge for a unit that only needs charged once a month would get a lot of play.
  • Snake Oil (Score:4, Informative)

    by gweihir (88907) on Wednesday January 13, 2010 @03:53AM (#30748260)

    Not enough energy available. Would probably not even offset self-discharging unless a pretty large antenna is used. You can fake a demo though with a highly directional antenna to beam in a wireless signal. Not realistic at all and inefficient as hell.

    I am constantly amazed at what people are willing to believe.

    • Re: (Score:3, Insightful)

      by Spatial (1235392)

      I am constantly amazed at what people are willing to believe.

      Ignorance makes you gullible. And in general people are pretty ignorant about technology.

    • But why... Why would anyone ever do such a thing!

    • Re: (Score:3, Interesting)

      by natehoy (1608657)

      They didn't even need to do that for this demo. They "pre-charged" it using WiFi, with no indication of how long it took to charge. They probably had to have the prototype built back in June or July and set it right next to a dedicated access point dialed up to "11" since then to get enough charge to top a Blackberry from 30% to 100%.

      If they're really lucky, they'll have the SAME device recharged for CES next year and it can charge a Blackberry from 0% to 100%. They'll have to have 4-5 more access points

  • There ain't no RCA (Score:3, Informative)

    by Wansu (846) on Wednesday January 13, 2010 @04:12AM (#30748334)

      Plus, don't let the RCA brand fool you into thinking this must be from a legitimate company: RCA hasn't existed as anything more then a licensed brand name for a couple of decades.

    You got that right. Neutron Jack cannibalized RCA in the late 80s, selling the consumer electronics division to Thompson. About 12 years ago, they sold chinese company TCL the right to use the RCA name on TVs and other products.

    They ought to replace Nipper with one of those chinese hounds with all the extra folds of skin. HIs master's voice is in chinese.

  • by Sockatume (732728) on Wednesday January 13, 2010 @04:28AM (#30748404)

    Nokia proposed a power-harvesting (and power-sipping) handset over the summer last year, to derive its power from cellular signals rather than wi-fi. Although their target amount of 50mW is way off, they claim to have a prototype that can pull in a few milliwatts, which inspired a mixture of scepticism and existential terror from researchers in the field.

    • by gweihir (88907)

      Nokia proposed a power-harvesting (and power-sipping) handset over the summer last year, to derive its power from cellular signals rather than wi-fi. Although their target amount of 50mW is way off, they claim to have a prototype that can pull in a few milliwatts, which inspired a mixture of scepticism and existential terror from researchers in the field.

      That would be very incompetent researchers then, as the "a few miliwatt" figure is very old and typically found in a classical radio experiment for teenag

  • Wireless power transfer is possible, for example MIT researchers have shown it to work across 2 metres in 2007 (see http://web.mit.edu/newsoffice/2007/wireless-0607.html [mit.edu]).

    The crux is to use "Magnetically coupled resonance" to achieve efficient power transfer to prevent the vast majority of power from being broadcast into space (read wasted) when no receiver is present to absorb it. Unfortunately that very feature seems to severely limit the transmission range.

    So I wouldn't worry about long-distance powe

  • Any device that radiates enough energy in a given frequency band to be equivalent to even the smallest battery would be illegal under the current FCC guidelines.

    Wireless Power Calculator
    http://powercastco.com/wireless-power-calculator.xls [powercastco.com]
    http://www.powercastco.com/resources/ [powercastco.com]

    Doing a simple calc with the above spreadsheet at 2.4 Ghz, 1W of radiated power, patch antenna, and five meters distance from the radiated power source, you would have just 0.040 mW of usable power, and at that, not enough to l

  • by GuyFawkes (729054) on Wednesday January 13, 2010 @07:34AM (#30749170) Homepage Journal

    Tesla was a very clever man, but his experiments (tesla coil etc) were based on something quite different than "broadcast energy".

    Tesla played with "harmonic" or "tuned" energy, eg take two tuning forks tuned to the same frequency, tap one to set it going, and hold it three inches away from the second one, the second one will start to vibrate, you just transferred energy.

    The primary and secondary circuits in a tesla coil works the same way, not with sound, but with tuned electromagnetic force, it is a tuned step up transformer.

    The SINGLE wireless power experiment that worked recently worked on the same principle, tuned magnetic coupling.

    ***This*** device is about simple absorbtion, so yes, it *will* absorb power, and yes it will *charge* a battery, technically speaking, so will your old external TV antenna, satellite dish, ham radio antenna, and indeed how the hell do you think the old crystal / cats whisker radios worked without a battery? It works for RFID too.

    But *practically* the rate of "charge" you get out of this is going to be less than the rate of self discharge, even for s single AAA size rechargeable battery.

    The physical analogy is a steel plate placed in the bottom of an empty swimming pool with indeed grab water condensation from the air overnight and "charge" the swimming pool with water.

    It will NEVER fill the pool though, the self discharge (evaporation) is a faster and more robust process.

    I though slashdotters were supposed to be educated?

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