Re: Tesla Coil RF Transmitter

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: William Beaty <billb@xxxxxxxxxx>

On Fri, 23 Sep 2005, Tesla list wrote:

> Original poster: Steve Conner <steve@xxxxxxxxxxxx>
>
> But! Is it not the case that a standing wave can't
> transmit power, by definition?

Then microwave ovens can't cook food!


I think you're referring to the fact that, when standing waves are present
and no absorption exists, then energy isn't propagating on average, since
the power vector of the two waves cancels out in the long term (and in the
short term it oscillates back and forth over half a wavelength rather than
proceeding forwards.)

But if there is an EM field present, that means an absorber (an antenna)
could extract energy from it.   And, if an absorber is present, then the
power vector would be directed inwards towards that absorber, indicating
that the energy stored in the standing wave was flowing into the absorber.

Where wireless energy transmission is concerned, the real goal of
planet-wide EM standing waves is to take advantage of the greatly
increased coupling caused by resonance. For example, a tuned-primary,
tuned secondary air-core transformer has tight coupling, it resembles an
iron-core transformer.  But if we remove the tuning capacitors, the
coupling becomes extremely small.  Or going in the other direction, if we
design the two resonators for extremely high Q, and also place the tuned
primary and secondary inside a high-Q resonant cavity, the value of
coupling becomes much higher.  Ideally the transmitter and receiver coils
would behave as if they were linked by an iron core.  And as with any
contemporary power transformer, the load would "draw" energy from the
power supply.  This is very different than, say, a microwave power link
where the transmitter sends out EM energy at a constant rate, and if the
load doesn't intercept it, that energy is lost.


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William J. Beaty                            SCIENCE HOBBYIST website
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