John Larkin wrote...
This very group had an extended thread on this subject, started by
Mr Beaty as I recall. Nothing he says is remarkable: a short antenna
can be matched with a high-Q tuning network such that it radiates
like a longer antenna. And antannas are reciprocal devices. So a
short receive antenna can be tuned to radiate or gather as much
energy as, say, a half-wave dipole. It just takes a very high-Q
matching network; the smaller the antenna, the higher the Q.
Indeed, a standard part of Poynting vector classical EM physics,
and antenna design. One could start their investigation with the
nice article by CF Bohren, "How can a particle absorb more than
the light incident on it," Am J Phys 51 (4), April 1983, pg 323,
and follow the citation links. For example, ZB Wang in Physical
Review B 70, pg 035418, 30July 2004. It's also become a newly-
interesting subject in the high-tech field of nanoparticles, e.g.
S Papernov, J Applied Physics 92 (10) pg 5270, 15Nov 2002.
A useful way to think of the scene in energy terms is to realize
that very small antennas have a high impedance, hence the required
high-Q network. It becomes a matter of extracting energy at high
voltages and low currents (from the external field). Even though
the resonant currents may be fairly high, one cannot directly
extract this as the Q would be spoiled.
Alternately, consider low-frequency active receiving antennas,
which are very short compared to the wavelength. These dispense
with trying to extract the energy, and the high Q required, and
simply use a high-impedance preamp to grab the antenna voltage.
The only resonant elements involved would be parallel series LC
traps, tuned to attenuate strong (local) RF sources that would
otherwise overload the wideband preamp.
The ball-lightning and stuff seems over the top, though.
Well, ball lightning is certainly another story.
