back to article Energy scavenger eats leftover wireless signals

No, it’s not another cute-but-useless contactless charger: a group of researchers led by Manos Tentzeris at Georgia Tech are working on antennae that could scavenge stray wireless signals to power small sensors or microprocessors. If you’re close enough to a large radio transmitter, harvesting stray energy is pretty …


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  1. Shanghai Tom

    Energy Scavenger - I remember when .. ..

    As an exercise in "green" electronics, some 40 years ago, I built a two tuner radio using low power transistors, the first tuner was used to hunt for a signal strong enough to put static through a crystal earpiece - and was normally Long Wave Radio 2 , the second tuner was then used to locate the station I wanted to listen to.

    For extra boost the aerial could be crocodile clipped to a wire fence / frame ( such as a bed frame ) and provided free listening almost anywhere. It was also built from Balsa wood about the size of 20 ciggies.

    I live in a city saturated with WiFi provided by a Telecom providor, so it would be quite feasible to suck all that free energy instead of hunting for a radio broadcast station.

  2. Vic

    Hasn't this been done before?

    ISTR some guy getting done for stealing power from Radio 3 transmissions by putting a huge coil of wire in his loft.

    The problem with using this against broadcast treansmissions is that there is no "leftover" signal; someone is paying to put that signal out and is trying to get as much distance as possible from that transmission (subject to licencing conditions).

    Inducing it to power kit just means less signal for someone else.


    1. Mako
      Black Helicopters

      RE:Hasn't this been done before?

      Given the low power, I doubt we'll see a widespread commercial application for this anytime soon.What useful work could it do for the average person? Charge their watch maybe?

      What I CAN see is a whole bunch of guys in MI6 sitting bolt upright in their seats with the realisation that this could enable indefinite unattended surveillance...

      Wonder how long it'll be before they can draw enough juice to run an ornithopter with a mic and camera?

      1. Fred Flintstone Gold badge

        Emergency torches

        These things classically lie around until they are needed, but at that point the batteries have usually gone. A small white LED and capacitor on a tWiFi fed treackle charger would be ideal. I'd buy a bunch - that is, if it's priced sensibly.

        1. Anonymous Coward
          Anonymous Coward

          No thanks...

          I'd prefer syrup.

      2. Anonymous Coward

        re: a whole bunch of guys in MI6 sitting bolt upright

        more likely they'll be asking how you got hold of their highly classified design specifications - probably time for you to start worrying

  3. Mips

    Not original

    We MK already make a remote hand-held lighting control equipment that is battery free collecting energy from the aether.

    By the way nice comment: "causing cancer (or not), headaches (or not), or irrational panic (too often)". Nail on head.

    1. Fred Flintstone Gold badge

      OK, details please..

      I've had for 2 years the idea that slowly accumulating WiFi energy would be a good way to reverse the normal trend of an emergency torch to STOP working after a while (the classic "a torch is a case with which to carry dead batteries" symptom). As LEDs use a lot less power there ought to be enough there to drive at least one simple HiBri LED..

      Having said that, Maplin does a fun baby LED keyring with a crank. It's got a capacitor inside, and a few secs of cranking gives you all the light you need. You just need to change the chain - it sucks. In addition, I have this habit of bolting an emergency light near where the fuse box is - the best light is one that is there where you need it :-).

      1. paulc

        Light by the fuse box?

        You have to be able to get to the fuse box first...

  4. Anonymous Coward
    Anonymous Coward

    How will they charge you for this energy harvesting?

    When they've worked that out they'll start taxing rainwater harvesting!

    1. Zimmer

      Too Late!

      They already tax the harvesting of rainwater by rating commercial buildings by their area under the guise of 'drainage'....

    2. Anonymous Coward
      Anonymous Coward


      If you a UK householder and can prove all the water that falls on your roof stays on your property and doesn't go down the storm drains, you can get a discount off your sewerage charge.

  5. Timo

    isn't this how those experiment kit radios worked?

    If I'm not mistaken, the "cats whisker" type radios that we built as kids from the box of electronic experiment kits did not use batteries, which means that they harvested AM radio signals to drive a speaker.

    And many of today's passive RFID tags are powered by the reading signal.

    The fact that the GT team captures spurious signals appears to be the only part of this that hasn't been already done before.

  6. Anonymous Coward
    Thumb Down

    Another bad 'green' idea

    So if you want TV or Cell-Phone reception and there is one of these things between you and the base-station/transmitter you're out of luck, wonderful. I hope that wasn't an emergency call you needed to make!

    1. sisk

      Not quite

      If that were the case then why don't you loose signal when there's another reciever between you and the transmitter? This is the same thing, only instead of decoding the signal it's using it to power something.

      And it's nothing new. One of the various electronics kits I had as a kid had instructions for building a radio that didn't need batteries. The summary of how it worked was pretty much the same as this, except that it used a much smaller range of signals to gather power.

      1. Vic

        Re: Not quite

        > why don't you loose signal when there's another reciever between you and the transmitter?

        You do.

        The more efficient an antenna, the more measurable is the shadow behind it. With most broadcast media, this is rarely a problem, because there is plenty of signal and the antennae in question are very inefficient at harvesting energy.

        However, attempting to make a (relatively) high-efficiency antenna that works over a broad band is likely to upset that situation.


  7. John Smith 19 Gold badge

    Interesting thing about this is the *bandwidth*

    Conventional RFID systems rely on a narrow band *resonant* antenna tuned to the powering frequency which is nearby.

    The implication is that this can absorb *any* signal of whatever power level in Ghz of bandwidth.

    Systems wise it's the difference between a taxi radio system (private base station) and a cell phone.

    From my very dim recollection of broadband antenna design in the 80s they may be using spirals rather than straight sections.

    Note that such antennas would make good RD shields or primitive bug detectors, If you're in the middle of nowhere inside an enclosure with 2 layers of these things and the *inner* layer is picking up a power reading when all your laptops/PMP/whatever are switched off you're carrying something.

    1. Asiren

      Since it absorbs *any* signal

      Doesn't this double up as a shield as well? So you wrap your building in this signal-sucking antenna, keeping all your WiFi signals inside AND generating/recovering some micro-energy for your site?

    2. amanfromearth


      Given that they need to print the antenna, I expect that is probably a fractal.

  8. Anonymous Coward

    Infra Red

    Heard much about doing this with infrared to generate solar power.. but then no products yet what going on...

    1. Lyndsay Williams
      Thumb Up


      This is a practical idea but very old. Crystal radios and antennas have been shown to power a Light Emitting Diode. Some Microcontrollers now work at 0.9V or less. A computer powered by this technology has many useful applications.

  9. Anonymous Coward
    Anonymous Coward


    It could be possible to power a wristwatch from picking up stray signals from cellphone towers.

  10. b-a-r-k-i-n-g-m-a-d


    "I've had for 2 years the idea that slowly accumulating WiFi energy would be a good way to reverse the normal trend of an emergency torch to STOP working after a while (the classic "a torch is a case with which to carry dead batteries" symptom). As LEDs use a lot less power there ought to be enough there to drive at least one simple HiBri LED."

    Those crank torches are an option - but mostly they are pretty cr@p.

    Just make life easy and fit either hybrid NiMH rechargeable cells (like Sanyo Eneloop) or better still Energiser Lithium (primary) cells - the latter has a shelf life of 5-10+ years. In an emergency do you really want to be cranking a torch for a couple of minutes use.

    Keep some spare cells handy and remember to check / recharge it every year.

    1. Marky W

      Thanks, Dad!

      Found any use for all those wood off-cuts and old hinges yet?

  11. Anonymous Coward

    Probably defeats the object...

    Probably defeats the object - i.e. if too many people 'harvest' (steal) these signals they companies may have to 'up' the power = more cancer, headaches (if you believe that) and more cost passed on to us 'the consumer'.

  12. Anna Logg
    Thumb Down

    what a silly idea

    I agree with Vic and Paul Turner, this is a daft idea, most of this 'stray' energy has been transmitted with a purpose, and that purpose wasn't providing someone else with a very inefficient source of 'free' power.

    Good luck trying to make a mobile phone call with a few dozen of these things attenuating the signal between you and the base station.

  13. Frederic Bloggs

    It's illegal

    There have been at least two cases of farmers being successfully prosecuted for "stealing electricity" by lighting their animal sheds (or some such) with fluorescent tubes powered by a nearby BBC transmitter or HV power lines.

  14. You're all dinosaurs

    Space power

    Could this be of use to the space industry? There must be huge amounts of radio energy washing out from the sun, through the Earth's radiation belts. Jupiter and Saturn are allegedly awash with radio energy - could probes use this to recharge their batteries instead of carrying radioisotopic power generators?

  15. KitD

    What's the decimal point?

    "hundreds of microwatts" sounds SO much better than "a few milliwatts"

  16. Anonymous Coward
    Anonymous Coward

    Technically interesting, maybe.

    Sustainable and economical? My arse.

  17. Solomon Grundy


    Aren't these "stray" signals alreadly licensed by the companies that send them out? This will never become mass market until someone gets the billing sofware worked out.

  18. Anonymous Coward
    Anonymous Coward

    No! Don't do it!

    It's hard enough getting a decent signal on an iPhone without people leeching the signal.

  19. Kevin McMurtrie Silver badge

    Tune higher

    There are already devices that can turn a few hundred THz into a tiny amount of power - solar cells.

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