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Cellphones Power

Nokia Developed Wireless Power-Harvesting Phones 246

Al writes "An engineer from Nokia's UK research labs says that the company is developing technology that can harvest ambient electromagnetic radiation to keep a cellphone going. The researcher says that his group is working towards a prototype that could harvest up to 50 milliwatts of power — enough to slowly recharge a phone that is switched off. He says current prototypes can harvest 3 to 5 milliwatts. It will require a wideband receiver capable of capturing signals from between 500 megahertz and 10 gigahertz — a range that encompasses many different radio communication signals. Other researchers have developed devices that can harvest more modest power from select frequencies. A team from Intel previously developed a compact sensor capable of drawing 6 microwatts from a 1.0-megawatt TV antenna 4.1 kilometers away."
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Nokia Developed Wireless Power-Harvesting Phones

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  • Crystal radio (Score:5, Informative)

    by davidwr ( 791652 ) on Wednesday June 10, 2009 @07:02PM (#28286809) Homepage Journal

    Crystal radio sets [] harvested enough power to drive an earphone-sized speaker.

    In some circumstances, florescent light bulbs can draw enough power from a nearby power source to light up.

  • Re:Why not solar? (Score:2, Informative)

    by j0se_p0inter0 ( 631566 ) on Wednesday June 10, 2009 @07:16PM (#28286929)
    Well yeah, I thought of that. But if my battery was low and I didn't have a charger, simply leaving it in a windowsill or something would be a pretty handy feature.
  • Huh? (Score:4, Informative)

    by wsanders ( 114993 ) on Wednesday June 10, 2009 @07:16PM (#28286943) Homepage

    Most of that power would be absorbed by some material, nearby concrete, or ground.

  • by geekoid ( 135745 ) <dadinportland AT yahoo DOT com> on Wednesday June 10, 2009 @07:30PM (#28287089) Homepage Journal


    Mahlon Loomis used radio for wireless transmissions in 1868. about 25 years before Tesla.

    Tesla created a circuit for doing it, but he wasn't the first and it isn't the only way.
    Cool boat, tho'.

  • Re:Henrich Hertz (Score:5, Informative)

    by Accursed ( 563233 ) on Wednesday June 10, 2009 @07:38PM (#28287145)
    It's more an electrochemical signal, though, not really anything to do with the energy of radio waves. It's electrical in the sense that it's charged (ions), not in the sense that there's an actual stream of electrons moving along like wires.
  • Re:Why not solar? (Score:3, Informative)

    by sznupi ( 719324 ) on Wednesday June 10, 2009 @07:45PM (#28287211) Homepage

    Interesting...the holsters disappeared from here long time ago. They were only somewhat popular at the very beginning of cellphone availability...mostly as a pseudo status symbol.

    I don't miss them at all.

  • by TinBromide ( 921574 ) on Wednesday June 10, 2009 @07:50PM (#28287241)
    no more so than a bunch of radios tuning in. If an antenna or chunk of metal is between you and a signal, your signal quality will be degraded. If not, you have a virtual line of sight (or LOS via reflections from the ground, buildings, etc) and can receive like normal. Its like worrying about your lawn receiving less light because your neighbor has solar panels on his roof. If the panels were between you and your lawn, it wouldn't matter if they were generating power, or just made of plywood, your lawn would be in the shade, but since they're not, your grass will be just as green. Its not like these antennas suck up the power, it won't bend the radio waves towards it like a magnetic pole would affect magnetic fields.
  • by Anonymous Coward on Wednesday June 10, 2009 @07:55PM (#28287265)
    I call BS on the phone call. I think your prof may have been pulling your legs. For one thing, 60 watts is a drop in the bucket compared to megawatt transmitters, for another, radio waves behave like light waves, there isn't a return loop or any sort of return transmission involved in radio waves.
  • Re:Crystal radio (Score:4, Informative)

    by FooRat ( 182725 ) on Wednesday June 10, 2009 @08:44PM (#28287697)

    this could result in a non-trivial reduction

    6 microwatts from a 1MW antenna - so a "mere" 166000 phones charging off just one transmitter would sink a massive 1W, or one millionth of that transmission power ... that sounds trivial to me.

  • by mpoulton ( 689851 ) on Wednesday June 10, 2009 @08:59PM (#28287825)

    Its not like these antennas suck up the power, it won't bend the radio waves towards it like a magnetic pole would affect magnetic fields.

    Well, actually they do. It's not at all significant in the grand scheme of things, but antennas do affect (reduce) the signal in the area near them. Antenna designers refer to an antenna's "aperture", the effective area in space from which it can "suck" signal. This is a very abstracted view, but is a useful analogy to understand how antennas affect electromagnetic waves passing near them. It is as if your power-sucking cell phone device creates a radio shadow a couple feet in diameter, instead of only the size of the antenna. Fortunately, the effect only extends a few wavelengths from the antenna at most (the so-called near field region) and has absolutely no impact on receivers outside that space.

  • Re:Henrich Hertz (Score:5, Informative)

    by Ungrounded Lightning ( 62228 ) on Wednesday June 10, 2009 @09:16PM (#28287971) Journal

    Hertz came up with the math for (transverse) electromagnetic waves.

    Tesla was into broadcast power - which he apparently visualized as using capacitive coupling to the ionosphere at high impedance and low frequency) along with conduction in it and the ground below it as the transport medium. That's just electric fields and conduction (or longitudinal waves in the ionosphere's plasma) rather than electromagnetic waves.

    It happens that his systems would also generate electromagnetic radiation and propagate power with it. But it's apparently not the particular mechanism he had in mind. (It's also not as efficient as the one he envisioned, since EM waves radiate in all directions and falls off as inverse square, while Tesla's system would essentially pump energy into a resonant cavity and contain it between the ground and the ionosphere until it was dissipated by loads or parasitic resistances).

    Now the devices in question in TFA are designed around Hertz's EM radiation rather than Tesla's "elevated capacitance" system. But it was Tesla, not Hertz, who was the big cheerleader for broadcast power using electric and magnetic phenomena (if not precisely Hertizan waves).

  • by shadanan ( 806810 ) on Thursday June 11, 2009 @01:34AM (#28289723) Homepage

    Can a device like the ones we are discussing actually "pull" more power from the source if present ?

    Yes, the process uses inductive coupling and works just like a transformer. []

    There are two ways to transfer energy wirelessly. Either you couple the receiver to the transmitter using the near field (inductive coupling), or you obtain the energy from the radiated energy in the far field (electromagnetic radiation). []

  • by pipedwho ( 1174327 ) on Thursday June 11, 2009 @03:42AM (#28290369)

    Not entirely true.

    When I was working for the Australian Telecom monopoly back in the late eighties. We had a problem with one of our coastal emergency radio transmitters (100kW iirc) that continuously broadcast a beacon and emergency information out to sea.

    Someone living in the vicinity of the transmitter decided they could power their house lights off our transmitter. This deformed the beam pattern in that direction and created a radio blind spot that was over 50km wide at the horizon.

    It wasn't hard to track the guy down. But, since this was a 'disruption of national communication infrastructure' issue, the federal police became involved and one of the offences for this was listed as 'treason'. I kid you not. These days it would probably come under some ludicrous 'terrorist' law.

    In the end, the guy got a slap on the wrist and promised not to do it again. But, it goes to show, that syphoning power off a transmitter can indeed have non-trivial consequences.

  • Re:Crystal radio (Score:3, Informative)

    by Timmmm ( 636430 ) on Thursday June 11, 2009 @05:45AM (#28290881)

    Well it was a few mW received from a 1 MW transmitter. So.... 12 zeros...

  • Re:Henrich Hertz (Score:3, Informative)

    by Sique ( 173459 ) on Thursday June 11, 2009 @06:27AM (#28291023) Homepage

    No, Mahlon Loomis may have invented a kind of long wave radio with his kites, but he had the theory behind it wrong. He was theorezing about layers in the atmosphere that carry a current, while Heinrich Hertz was correctly pointing out that it was electromagnetic waves he was demonstrating. Of course, Heinrich Hertz had the big advantage of knowing James Clerk Maxwell's Theory of Electromagnetism (1879), and he was indeed looking for an experiment that could test if radio waves have the same characteristics (e.g. transversal wave travelling at the speed of light) as light waves.

  • by shadanan ( 806810 ) on Thursday June 11, 2009 @09:50AM (#28292855) Homepage

    Your example is actually an instance of the second form of energy transfer using the far field. Photons are the carrier particles for electromagnetic radiation. []

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