Wireless power transmission in the HF region is definitely not a 'green'
technology, with efficiencies hovering around 60% at best for any useable
separation distance. Of course, if you make the distance zero then efficiency
can be more like 96% -- it's called a transformer. Better yet, use wires and
get 99+% for a well designed interconnect, at a tiny fraction of the price of
wireless. Maybe I should patent that... Given the low efficiency of the MIT
scheme and for other reasons that resonate (so to speak) at multiple levels, I
refer to wireless power as a 'brown' technology.
Also note that the MIT psuedoinvention has a scaling issue. Want two meters
distance at about the same efficiency? Then use two meter coils! Ten meters?
Well, you get the idea. I suppose that you could power everything in a house
by putting a pair of coils on the outside walls, assuming you are willing to
live in the EM field of a giant helmholtz coil and pay electric bills that are
twice normal.
The comment about 10MHz being a protected frequency is absolutely correct. I
was appalled that the MIT folks were so clueless.
There has been some serious work at microwave frequencies, where it is
possible to at least focus the energy. One company
http://www.powerbeaminc.com/industry.php uses infrared laser diodes at 214
THz. As yet unexplored is the possibility of using giant fans to turn your
house into a wind tunnel so miniature wind turbines can power your appliances,
all in the name of avoiding efficient, cheap, and simple power cords.
Orin Laney
On Tue, 18 May 2010 06:25:31 -0700 "Price, Edward" <[email protected]> writes:
I recently read a follow-up on wireless transmission of energy. Back
maybe as
long as last year, there was a burst of publicity about a prof at MIT(?) who
had created a demonstrator of energy transfer. The demo showed about a 1
square meter, several turn, flat coil transmit and a similar receive antenna;
the separation distance was also about a meter. The receive and transmit
antennas had parallel tuning capacitors, and the receive antenna drove a 40
Watt incandescent lamp (not clear if the lamp was in series or parallel with
the capacitor).
OK, the point is that I was surprised to see transmission of 40 Watts
over a
meter. At the time, the tech details were slim, but the follow-up points out
that the operational frequency of this demo was 10 MHz! And the efficiency was
somewhere around 10%. Of course, the prof wasn’t claiming anything about
efficiency, he just wanted to show the transfer demonstration.
My immediate reaction is that he was pumping out maybe a half kW at 10
MHz!
Didn’t anybody notice that the room felt strangely warm, and that some
digital cameras did strange things? My second reaction was that 10 MHz is an
internationally protected frequency (no emissions allowed at all, to protect
time-standard signals). He might at least move on over to 13.56 MHz.
In any case, all these schemes about wireless power transmission seem to
crash on the shores of acceptable human exposure. Remember those wild schemes
>from the 60’s, where huge orbital solar arrays would convert sunlight to
microwave, and then beam it back to Earth? Maybe that’s where the concept of
aluminum foil hats originated!
Ed Price
[email protected] <blocked::mailto:[email protected]> WB6WSN
NARTE Certified EMC Engineer
Electromagnetic Compatibility Lab
Cubic Defense Applications
San Diego, CA USA
858-505-2780
Military & Avionics EMC Is Our Specialty
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