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Is RCA's Airnergy Snake Oil?

Posted by kdawson on 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?"

7 of 271 comments (clear)

  1. Yeah, tens of meters from a 50mW power source... by francium+de+neobie · · Score: 5, Insightful

    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.

  2. In answer to the headline, let's simply say by MrEricSir · · Score: 4, Insightful

    YES

    --
    There's no -1 for "I don't get it."
  3. Re:Yeah, tens of meters from a 50mW power source.. by Zondar · · Score: 3, Insightful

    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.

  4. back to basics by vacarul · · Score: 5, Insightful

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

  5. Re:Yeah, tens of meters from a 50mW power source.. by PhilHibbs · · Score: 3, Insightful

    You're blocking the signal by absorbing large amounts of it. A shared resource should be shared, and not abused.

  6. Well two things by Sycraft-fu · · Score: 3, Insightful

    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.

  7. Re:Yeah, tens of meters from a 50mW power source.. by aXis100 · · Score: 4, Insightful

    Frequency plays a massive difference in EM radiation and magnetic induction.

    For EM, you really need an antenna that's close to the wavelength, and for 50Hz that's 6000km. For 2.4GHz it's about 12cm.

    For induction, frequency affects the overall number of turns required. A 50Hz transformer that copes with 300W is the size of a shoe box, but for a switchmode power supply at 100KHz it's the size of a match box.