Here's something which should be interesting to play with, and might lead
to some fascinating engineering applications, or at least aid our
understanding of some of the more obscure electromagnetic lecture demos.
This is from the earlier thread "Teeny atoms absorb huge EM waves." I
added it to my website recently, so people here might not have encountered
it as yet.
Use a dipole antenna to gather EM waves. If your antenna is <<
wavelength, then what happens if you *transmit* a cancelling wave which is
phase-locked to the incoming waves being absorbed? This will partially
cancel the energy in a significant part of the nearfield region of your
antenna. Since the antenna is so small, it does not radiate much EM, so
the effect only applies to the nearfield region. At low frequencies this
region is titanic. But this is impossible! Energy cannot simply vanish!
You are correct sir.
When the "cancelling wave" has grown to maximum, the antenna is "sucking"
a poynting-flow out of the entire nearfield region surrounding itself. The
intense AC electromagnetic fields generated by these devices act as a type
of enormous "virtual EM funnel." By manipulating the e- and b-fields of
the nearfield region separately, we can change the power and hence the
effective area of the receiving antenna. For example, by actively
increasing the b-field surrounding an electrically small loop-antenna,
while leaving the e-field alone, we can hugely increase the rate of EM
energy being intercepted by the antenna.
What's really cool is that these are passive devices. Any resonant
circuit of extremely high "Q"-factor will build up the desired
phase-locked active-cancellation field and become an "energy sucker." This
only ocurs if we use components which allow the fields within the coil
and/or capacitor to couple with the surrounding volume. A large square
loop-antenna built using large-diameter copper plumbing pipe would make an
excellent low-resistance coil. Superconductor vacuum-capacitors and coils
would be all the better. Or instead just extend a short whip antenna from
your hi-Q tuned circuit and connect the other terminal to ground, and
you'll see an immense AC voltage appear on the antenna as the "virtual
funnel" extends itself and begins to suck energy out of the weak ambient
fields of whatever distant transmitter which you've tuned the system to.
In physics the effect is hidden within the concept regarding the
"collision crosssection area" of particles. These areas change as the
particle energies approach certain resonant absorbtion values. The size
of your "barn" dance can vary wildly depending on whether your music is
"in tune." :)
This isn't high-energy particle physics, either. At resonance, a
1-angstrom atom can spread its field-nets outwards to 3000 angstroms and
punch a vast hole in the propagating light waves at 6000 angstrom
frequencies. For example, that's why sodium gas is so opaque to the
sodium-line spectrum, even though the individual atoms in the gas present
almost no cross-section to the incoming waves. (And perhaps it's also why
sodium bose-einstein-condensates can slow light down to a
propagation-speed similar to that of "heat conduction.")
In theory these concepts allow us to steal power from both AM antenna
towers and distant 60Hz power lines, transmit kilowatts from tiny desktop
antennas, perhaps explain the human hearing system and ball lightning,
build portable AM radios which need no longwire antennas... and
communicate usable power to planes, trains, and automobiles through a sort
of, ahem, "World System" VLF radio-energy distribution apparatus which
lets us use extremely feeble RF fields as the transfer medium for energy
flows greater than anyone could possibly suspect. The *receivers* develop
the intense EM fields, and this eliminates any requirement that we
transmit high-power radiation.
This stuff has always been around, but in my opinion modern engineering is
partially clueless about it. Physics is the same. It seems to be an
overlooked hole in physics which leads to a relatively unexplored realm.
I always knew that EM resonance was weird, but when I had an epiphany
regarding this stuff it gave me a serious case of brain-burn. (So what
else is new?)
I looked for conventional physics papers and discovered only two so far,
both of which were written in the 1980s. And one is by my hero Dr.
"Beer-Clouds" Bohren. If Chris Bohren has noticed this topic, then my
alarm bells ring wildly.