OMG. Popular Science Magazine finally comes true !?
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| Author | Content |
|---|---|
| BernardSwiss Jul 14, 2011 12:04 AM EDT |
Or was it Popular Mechanics? Probably both. And Tesla's smirking in his grave... |
| techiem2 Jul 14, 2011 12:11 AM EDT |
Sweet. |
| cr Jul 14, 2011 3:30 AM EDT |
To really scavenge rf emissions like that, they're going to have to come up with a better detector material. Silicon's forward voltage is something like 0.65v; germanium's is something like 0.25v. That forward drop is cut in half if they use a hot-carrier diode (the old AM-radio standby germanium point-contact signal diode is such, with about 0.125v forward drop), with a metal contact substituting for one of the doped areas, cutting the depletion region in half. That makes for a faster diode as well, but at the cost of low reverse breakdown voltage, so scavengers using them are vulnerable to high ambient rf environments. Not that most installations are likely to ever see that. Even with broadband antennas like that shown, the signal coming off the antenna is likely to be down in the tens of millivolts or lower in most human-occupied environments. That won't rectify in modern diodes without either a bias source or amplification, which defeats the whole purpose: if the circuit self-powers that bias or amplification, it's not self-starting. MOSFET synchronous chopper detectors don't do broadband. Unless I'm really missing something recent in analog, power or rf technology, they'll need a breakthrough semiconductor, something with a forward drop down where the signal is, to realize this dream. |
| JaseP Jul 14, 2011 11:46 AM EDT |
Yeah,... What he said... Seriously, though, it seams like this tech is either going to be, at best, a way to help sleeping devices lose less battery power, or to help make energy saving devices a smidgen more energy efficient. This isn't going to be able to make normal devices self-sufficient, with current tech, any way. |
| penguinist Jul 14, 2011 2:58 PM EDT |
Quoting:This isn't going to be able to make normal devices self-sufficient, with current tech, any way. Actually, we have micro power technology already. Look at the Texas Instruments MSP430. There you have a 16 bit microprocessor chip with plenty of onboard I/O and the current draw is only 165 microamps per MIPS while the cpu is active and only 0.7 microamps if you suspend the cpu but leave the clock running. The author claims to be producing "milliwatts of power" now using wideband approaches, with the potential of 50 milliwatts after further work. Seems like we have a match using today's technology. |
| cr Jul 14, 2011 5:40 PM EDT |
@penguinist: QRPp FTW. Hardware like that is great for saving power once you've got it, but running at what voltage? The problem here is fundamental: all the rf they hope to scavenge is AC. Since their scheme is broadband, they can't use synchronous techniques to detect (rectify) the received signal, so they're left needing to get that signal high enough in voltage to pass it through a rectifier, which has a very nonlinear threshold below which it just plain won't conduct. Working from my experience as a homebrewer radio amateur, I can maybe see them bringing the signal in from the antenna through a ferrite-loaded broadband transformer, trading bandwidth and amperage for voltage, but not if the antenna impedance is already high, which is how physically small antennas like the one shown tend to be. Even then, to make it work, they'd need to bathe it in ambient rf at a level which is unhealthy for people and thus generally inaccessible. (In 1978, QST carried a note about the fact that radio amateurs as a group have a leukemia incidence 4 times that of the general populace; high ambient rf does things to people no matter what the wireless/cellphone lobbyists say. These days, FCC Part-15 testing as part of type-acceptance protects people in the name of protecting the airwaves. I do believe that Tesla's wireless power transmission idea, if implemented, would have slow-motion killed us, as demonstrated by the Amana Radarange.) I see this as a clever experiment, leading to being able in some corner cases (close encounters with square-law) to trickle-charge or chargetime-boost other power systems. The research into extreme-wide-bandwidth receiving-antenna design will be useful in other areas such as surveillance and cell-phone node systems. I don't see this as being useful in daily life unless and until we find a semiconductor material with a much lower forward voltage and get good at finessing wafer fabs to use it. |
| penguinist Jul 14, 2011 7:05 PM EDT |
@cr: You are spot on correct that the challenge would be "detection" of the signal in a way where some efficiency was achieved, and I agree that conventional silicon, germanium, or schotky diodes would provide too high a voltage drop to be useful. Too bad the author of this article doesn't give more details. He claims to be harvesting "milliwatts" of power and claims that 50 milliwatts is achievable. Perhaps he has a novel detection technique which he is not disclosing. |
| helios Jul 14, 2011 8:58 PM EDT |
And Tesla's smirking in his grave... Foss should learn from the Tesla vs. Big Business Tycoons. Between Edison and Westinghouse, Tesla's ideas were crushed and some were buried. It was a tragic loss for the world...I can only imagine where we would be now. Of course, when you start screwing with a planet's magnetic field... |
| dinotrac Jul 14, 2011 10:07 PM EDT |
@helios -- At least the nifty little guns are still around to keep Warehouse 13 safe. |
| cr Jul 14, 2011 10:18 PM EDT |
Quoting: Too bad the author of this article doesn't give more details. He claims to be harvesting "milliwatts" of power and claims that 50 milliwatts is achievable. Perhaps he has a novel detection technique which he is not disclosing. Or maybe he's slapping that antenna right up against his monitor or inside the computer's case to get it in the square-law (signal strength falls off as the square of the distance from the radiant source) corner. If his chosen rectifiers will switch that fast, he can also get a nice half-kilowatt boost from sticking it in the microwave oven and turning on the magnetron. He ain't saying, which is why I ain't buying. Most of my HF QSOs were QRPp and my early designs were heavily CMOS back when that meant working around the slowness of series-4000 metal-gate; I could really get into his trip if it weren't for that pesky semiconductor physics stuff. |
| helios Jul 14, 2011 11:04 PM EDT |
@ dino...and yea...Mika's back to shoot them. Errrr, not that I watch religiously or anything.... |
| JaseP Jul 15, 2011 8:38 AM EDT |
Mmmm,... Mika,... Not that I watch the show either (after the wifee goes to bed) or anything... |
| penguinist Jul 15, 2011 8:55 AM EDT |
Here is what they say about their detector approach which uses inkjet printing of a special emulsion:Quoting:However, they add what Tentzeris calls “a unique in-house recipe” containing silver nanoparticles and/or other nanoparticles in an emulsion. This approach enables the team to print not only RF components and circuits, but also novel sensing devices based on such nanomaterials as carbon nanotubes. You can read some more detailed coverage of this project here. |
| dinotrac Jul 15, 2011 7:54 PM EDT |
Hey, even secular humanists are allowed to enjoy watching Mika, but only True Believers in the High Gospel of Geek are allowed to enjoy watching Claudia. |
| helios Jul 15, 2011 11:23 PM EDT |
Dino....lecherous geeks at that...I would guess |
| dinotrac Jul 16, 2011 10:30 PM EDT |
@Kenny boy -- You say that like it's a bad thing. |
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