Is RCA's Airnergy Snake Oil? 271
Posted
by
kdawson
from the deepness-in-the-sky dept.
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?"
Yeah, tens of meters from a 50mW power source... (Score:5, Insightful)
The inverse square law and dBm being a logarithmic unit can all go to hell.
In answer to the headline, let's simply say (Score:5, Insightful)
YES
Re:Yeah, tens of meters from a 50mW power source.. (Score:4, 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.
Re:Yeah, tens of meters from a 50mW power source.. (Score:3, Insightful)
That really should have worked, with a sufficiently long antenna. It'll be induction, but that ought to count too.
back to basics (Score:5, Insightful)
Re:Yeah, tens of meters from a 50mW power source.. (Score:3, Insightful)
You're blocking the signal by absorbing large amounts of it. A shared resource should be shared, and not abused.
Well two things (Score:4, 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.
Re:Yeah, tens of meters from a 50mW power source.. (Score:3, Insightful)
Look again into that physics text. Frequency is denoted by "f", not "ny" (no, that is not a lowercase v). The formula you quote relates to the energy of a single photon, no voltage or current in there anywhere and is completely irrelevant to the discussion at hand.
Re:Snake Oil (Score:3, Insightful)
I am constantly amazed at what people are willing to believe.
Ignorance makes you gullible. And in general people are pretty ignorant about technology.
Re:Yeah, tens of meters from a 50mW power source.. (Score:5, 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.
Do **NOT** invoke Tesla (Score:3, Insightful)
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?
Re:Snake Oil (Score:1, Insightful)
Not enough energy available. Would probably not even offset self-discharging unless a pretty large antenna is used...
If it could offset self-discharge, that would be a nice feature for a portable battery pack.