All true, except in the case of evanescent waves, which are
exponentially attenuated, as in the case of the external waves
seen when you have "total internal reflection" in optics, or
more familiar to hams, a waveguide beyond cutoff. Mathematically,
you have an imaginary wavelength (wavenumber), IIRC.
I did some Googling and found the MIT paper by Soljacic here:
http://arxiv.org/pdf/physics/0611063
Beware - math & physics. The trick is to get slow enough
exponential attenuation. To answer my original question,
it seems that 6.4 MHz is the frequency for optimal power
transfer, given some particular geometry, i.e. a typical
room size, etc.
The authors seem to be theoreticians -- their claims really
beg for a little bench work!
73 Martin AA6E
Tom Rauch wrote:
>> Induction without a ferromagnetic material to contain the
>> flux still results
>> in a magnetic field in the air, and where there is a
>> changing magnetic field
>> there will be an electric field and therefore radiation.
>
> Radiation is caused by time varying current in conductors.
> It is an entirely different mechanism than the induction
> fields. Anytime there is charge acceleration there is
> radiation.
>
> The only way to prevent radiation is by creating an exactly
> opposing radiation. When that happens is just so happens we
> can't transfer a magnetic or electric field outside that
> boundary either. We shield or take any one field to zero,
> the others all go to zero too.
>
> If they are transferring energy via a time-varying magnetic
> field through space, or if they are conducting RF energy
> along conductors that don't fit the criteria of a very good
> transmission line, it will radiate. We can bet on it.
>
> I think BPL, EH antennas, CFA antennas, shielded magnetic
> loops, and other stuff like this come from people who don't
> understand how RF systems work or who want to pretend there
> is some sort of magic.
>
> 73, Tom
>
>
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