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Is RCA's Airnergy Snake Oil?
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?"
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.
Yes, when I am confronted with an RCA TV, the first thing I think is, "a legitimate company produced this."
the mythbusters tried to get power from the em radiation from a high voltage line. That doesn't work nothing will.
YES
There's no -1 for "I don't get it."
Not necessarily, frequency is just as important as voltage and current.
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.
I think it is the _change_ in magnetic flux that generates a current in a conductor, not just the presence of magnetism.
They whose government reduces their essential liberties for temporary security, receive neither liberty nor security.
Yes. Solar power from visual light (EM radiation) works very well. We know that.
http://michaelsmith.id.au
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.
Carry a cell tower... I think I'd rather carry a microwave oven - much more compact and convenient, since it can reheat my lunch too.
Excuse me, but please get off my Pennisetum Clandestinum, eh!
That really should have worked, with a sufficiently long antenna. It'll be induction, but that ought to count too.
Finally! A year of moderation! Ready for 2019?
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.
Nasa HAS tried this.
http://en.wikipedia.org/wiki/Electrodynamic_tether
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.
...unless you want to cook the user holding the phone at the same time.
Your ideas are intriguing to me and I wish to subscribe to your newsletter.
Literalism isn't a form of humor, it's you being irritating.
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.
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.)
Cellphones do not use 2.4Ghz, so the frequencies would not be jammed. The problem is that the people using them would be cooked or at least feel a slight pain.
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.
Tesla seemed to think this idea was workable. Can't say about RCA's product but I'll trust Tesla.
At what price learning? At what cost wisdom? The price is a man's peace of mind, and the cost is his life.
I'll get more energy with a hand-crank generator...
How can you steal that what is freely given? Laws are weird.
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.
Most ACs are not even worth the keystrokes to insult them. Be generically insulted by this and ignored otherwise.
You're blocking the signal by absorbing large amounts of it. A shared resource should be shared, and not abused.
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.
Wansu, th' chinese sailor
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.
Most ACs are not even worth the keystrokes to insult them. Be generically insulted by this and ignored otherwise.
Frequency effects your ability to absorb the energy. I can only pick up NSA broadcasts on my dentalwork, for example.
If you were blocking sigs, you wouldn't have to read this.
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.
No kidding!!! What do you say at this point?
Actually, the article says "At CES, the device's battery, which I believe was precharged with Wi-Fi power, was able to charge a BlackBerry from 30% power to full power in about 90 minutes." Note the "which I believe was PRECHARGED" part. So they managed to charge a Blackberry from a pre-charged external battery in 90 minutes. Yay. But they never actually said how long it takes to charge the battery in the Airnergy device via wi-fi signals - probably for a good reason, because that would take probably a couple hundred days or more.
Multiply it by the hundreds to thousands of cellphones within one cell ... can you imagine how much power the cell tower much emit in order to charge all those phones?
FWIW: the article says that the charger makes electricity from "ambient WiFi signals" -- not from the cell tower. Allegedly, at the trade show, "they were able to charge a BlackBerry from 30% to full in about 90 minutes."
That's amazing, because it takes that long to charge my POS cell from the wall with a ... hmmm... ya know, something just doesn't seem right here...
If you aren't suspicious of your government's actions, you aren't doing your job as a responsible citizen.
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.
You just failed physics 101. Frequency has absolutely no impact on energy in a signal.
Indeed, That's Why the the GHz Barrier was a myth, in fact we should have Thz machines if it weren't for the man keeping them down.
*cough*E = h*(c/lambda)*cough*
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
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.
Most ACs are not even worth the keystrokes to insult them. Be generically insulted by this and ignored otherwise.
I suspect the sun is putting out slightly more than 50mW, though...
The greek nu is the standard notation for frequency in physics, or at least it generally was when I did that kind of thing. f is sometimes used, though less commonly. However, photons are not relevant for RF - the photon energy is so small that the quantum nature of the radiation is not apparent, and it behaves for all practical purposes as a classical wave.
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.
Meh, according to the German broadcasting agency I'm already stealing radio waves by owning a computer.
I'm not kidding.
Well, try standing next to a microwave antenna.
You use the "nu" when dealing with particles. For waves it is f. In electronics it is practically always f.
Most ACs are not even worth the keystrokes to insult them. Be generically insulted by this and ignored otherwise.
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?
http://slashdot.org/~GuyFawkes/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.
Free Martian Whores!
Actually you only need about 1/4 of the wavelength to get a good antenna. A full wave antenna doesn't provide a good match for real work situations.
It's easier to fight for one's principles than to live up to them.
I believe the standard rule of thumb is ~ 1 kW / meter^2.
I can feel the energy from the sun on my hand. I can't feel the energy from a router. Not even with my EM allergies :-)