A reader writes:
They claim it will “harvest” energy from 2.4GHz devices, like wireless phones and WiFi devices. They say it can charge a cell phone from 30% to full in 90 minutes on the CES floor, which is confusing because of all the wireless devices on the CES floor and the fact that many cell phones report full early to make their batteries look better. Since a Wi-Fi device operates at 100mW and that shrinks with the inverse-square law, wouldn’t any Wi-Fi power be trivial?
Would this only be practical if you had a lot of overlapping Wi-Fi hotspots and/or a huge charger, or am I missing something? They’re even claiming they can integrate this into batteries in the future.
If this is a scam or borderline useless, why is RCA promoting it? I could understand this kind of trash from a fly-by-night operation like all the fuel-pill pages, but I would think RCA would want to keep some of its reputation.
Yes, I think this has to be some sort of hoax. I ain’t no RF physicist, but I don’t think the numbers add up at all.
(I am, unsurprisingly, not alone.)
The output of the very small charger for my very low-powered mobile phone (a Motorola F3) is specified as 6.4V @ 200mA, which is 1.28 watts. The output of a standard Wi-Fi access point is, as you say, limited by the spec to 100 milliwatts. And, again as you say, the laws o’ physics dictate that even if this thing contains a beautifully-engineered rectenna that hoovers up 90% of the 2.4GHz-ish RF energy that impinges upon it, it’ll still collect far, far too little power to do anything very useful. For the same reason, it is difficult for a device the size of a canoe to harvest much energy from the wake of a passing ocean liner.
It’s actually not quite as bad as you might think from a pure inverse-square law calculation, because the “impossible antennas” used in normal access points have a sort of inverse-hourglass-shaped radiation pattern, concentrating output around the antenna at the expense of output above and below it. If you’re lined up with the radiation pattern of one of the larger “omnidirectional” Wi-Fi antennas, you could easily be getting three or four times as much power as you’d get if it were a real omnidirectional antenna.
But unless the Airnegy is squished right up next to the antenna so it covers, and near-totally absorbs, some relatively large fraction of the entire radiation pattern (and, of course, thereby makes devices in its “shadow” unable to see the AP any more…), then the energy it’ll receive even from several out-of-specification half-watt Wi-Fi adapters will be extremely low. Never mind charging a phone - you wouldn’t even be able to light an LED.
(A crystal radio can run on the RF energy from its own antenna, but that’s in the microwatt range, at best.)
I suppose a device with some sort of broadband fractal antenna in it, that can suck up everything from 50Hz mains hum to high-gigahertz radar beams, might be more practical. But the Airnegy is said to be 2.4GHz-only.
Oh, and there doesn’t seem to be any mention of this product on the RCA site. And although the Airnegy CES stand looks professional, the products themselves look like quick mock-ups to me. Look at this battery, for instance. It looks as if they put a construction-paper wrapper around a standard battery.
(I presume someone’s paid to have the stand there, too, unless CES was having trouble filling the floor and let in hoaxers for free, like the funny fake ads that fill holes in newspaper classifieds.)
Note also that RCA is now, I think, one of those “zombie brands” that has been reduced to nothing but a logo that’s slapped on random Chinese flea-market gadgets. So even if it actually is a “real RCA product”, that doesn’t mean much any more.
This also isn’t a new idea. Here’s a piece about a “prototype Nokia phone” that’s supposed to somehow harvest five milliwatts from incident RF.
Can any readers who’ve got some of that fancy book-learnin’ about that thar electrickery help me out, here?
Has anything at all like this thing ever actually been made to work?
(And no, inductive chargers don’t count!)