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Registered Member #29
Joined: Fri Feb 03 2006, 09:00AM
Location: Hasselt, Belgium
Posts: 500
I think there is some science in the BBC article. There is nothing miraculous about it tho'.. It seems to be nothing more than inductive energy transfer not unlike what is used in RFID chips and thos electronic key cards that you wave in front of a sensor.
Essentially, in the "power supply", we have a resonant LC circuit that draws negligible power when nothing is near it (high Q, "long-lived resonances"). When you put your PDA equipped with an inductive pickup coil (perhaps resonant too) near the power supply's resonant circuit inductor, some power is coupled into the PDA's pickup coil and rectified and charges the battery. It is inherently short range....a few 10s of centimeters at best... I am sceptical about the "transmitting significant power over many meters" claim... I'd have to think about it a bit...
The thing I find absurd about this article is not that it may be BS, but the technology is older than I am...someone has just discovered that it can be made "fashionable" by charging your cute little electronic "lifestyle" devices with it.
Registered Member #63
Joined: Thu Feb 09 2006, 06:18AM
Location:
Posts: 1425
wrote ... The thing I find absurd about this article is not that it may be BS, but the technology is older than I am...someone has just discovered that it can be made "fashionable" by charging your cute little electronic "lifestyle" devices with it.
Mmm, that's why BBC is full of crap. =(
Here's good reading regarding the 'localized heating' argument re: the businessman/teenager and microwaves/EM through the head:
If little wireless energy transfer systems come into vogue, it'll give the activists a new lease on life, if power lines and mobile phones aren't bad enough. ^^
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
I guess I should clarify the statement I made that high Q=low efficiency, since intuitively you'd think the opposite. (Q is quality factor, and the higher quality something is, the more efficient it must be, right?)
Not necessarily. I'm referring to the loaded Q of the system as a whole, which is really more related to power factor than anything else. If the loaded Q of the power transmission system is, say, 100, then you have reactive currents (or voltages) 100 times higher than if you'd just transmitted the power directly with wires. That is the same thing as having a power factor of 0.01. Hence the losses (either I2R or dielectric) could be up to 10,000 times greater than with direct transmission.
That was one of the findings we took away from the work done on DRSSTCs in the last year or two. The unloaded Q of a Tesla coil can be several hundred, but once the streamer discharge is established, the loaded Q is about 10. It's also discussed at length in articles on RF power amp design.
P.S. For the frequencies and antenna geometries they seem to suggest, I think the loaded Q would be at least 100. (in other words, the coupling's maybe not that strong)
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"resonance" hype on BBC news
