long, very thin metal secondary coil ball | __ | __ / \ \|/ |||| \__/--========================||||====--| |||| _|_ primary /// Gnd connection coil fig. 1 A typical Tesla coilIf we wrap a single-layer coil of wire upon a very long plastic tube, we have a Tesla resonator as in Fig 1. In essence, this is an an electrical transmission line. We can inject AC into one end with a little primary coil wrapped around. Now look at Fig 2, where we place a SECOND "primary coil" at the far end. This second coil would act as a "receive" coil, and would collect the energy we had injected into the "transmit" coil at the other end. Since the long think coil is actually a single piece of wire, we've managed to send electrical energy along a single wire. There is no electric circuit involved! This only works because the long, thin coil can support slowly-moving EM waves, and the electron-sea of the wire in this coil behaves as if it has become compressible.
Now put a metal sphere on either end to prevent corona from spewing out of
the dangling wire tips, and we've built a simple electrical power system.
Put high-freq AC into the first "primary coil", and the same AC comes out
of the second "primary coil" at the far end. Choose the right load
resistor for the "receive" coil, and all of the electromagnetic energy
flowing along the long thin secondary will be absorbed without reflecting.
metal metal ball ball __ __ __ __ / \ |||| long, thin secondary coil |||| / \ \__/--==||||=============================================||||==----\__/ |||| (plastic rod wrapped with wire) |||| primary 2nd "primary" coil coil fig. 2 A single-wire transmission lineNote that this is a SINGLE WIRE transmission line! It apparantly uses LONGITUDINAL WAVES! However, there is nothing crackpot about it, since it obeys conventional physics: the propagating electric fields and magnetic fields which surround any part of the long coil are always at 90 degrees to each other. Successive waves of positive and negative charge move along the coil, and these waves are connected to each other with EM fields. The EM fields are transverse. The only thing that acts like a "longitudinal" wave or compression wave is the density of free electrons in the wire. Is this crazy? No. Within a normal piece of coaxial cable, the electrons of the metal move as part of a compression wave, even though the EM fields within the cable's dielectric remain part of a transverse wave.
In conventional cables there are two conductors, and the voltage between
them forms the "E" part of the EM wave. In the above one-wire coil
device, the voltage between the travelling lumps of net-charge distributed
along the long thin coil forms the "E" part of the wave. The single wire
acts as its own "circuit." The motion of the net-charge is an electric
current, and this creates the "M" part of the EM wave.
Interesting? A single wire transmission line! It doesn't violate the
rule forbidding longitudinal EM waves. However, it violates the
fundamental rule regarding electric circuits in that there *is* no
circuit here. The two ends of the system are connected by a single wire.
HOWEVER, this is not unique. Once long ago I encountered an article about
a single-wire transmission line. This had nothing to do with Tesla; it
was about an old microwave transmission scheme called a Goubau
transmission line or "G-line." The article was in an old copy of QST
magazine (amateur radio mag) in the 1960s or '70s.
It turns out that you can send microwave or UHF signals along a *single*
wire as long as that wire is coated with a dielectric. To do this, you
start out with a normal coaxial cable. You strip the shield from a
central section, then solder on a pair of large, cone-shaped copper horns
which attach to the coax shield at either end of the coax cable. The
dielectric-coated single wire extends between the ends of the coax. Sort
of like this:
hollow hollow cone ____ ____ cone _____----- | | -----_____ _----------- |______________| ------------_ -----------_____ | | _____------------ coax -----____| "G-line" |____----- coax cable cable fig. 3 The "G-Line"In the above diagram, the single-wire section between the two hollow cones can be as long as desired, but it must be fairly straight. Those cone-shaped parts must be about one wavelength across (or was it 1/2 wavelength? I don't remember exactly.) The metal cones act as "wave launchers" or "wave catchers". As the EM waves come out of the coax cable, the cones allow the waves to spread out and attach to the "G-line" part. There must be a plastic coating on the "G-line" wire, otherwise the waves will not lock onto it, and they will tend to wander away into space. The article noted that you COULD put a bend in the G-line, as long as it was a long, smooth bend of large radius. Because of the plastic coating, the waves would follow the bend. If there was no plastic coating, the waves would miss the bend and go straight out into space, missing the "catcher cone" entirely.
Obviously this can only work with AC. There is no electric circuit,
instead we have waves of "electron compression" which propagate along a
single wire. Let's quickly look at a fluid analog. The fluid analogy of
an electric circuit is a closed loop of water-filled hose. To send energy
to any part of the loop, we simply force the water in one part of the loop
to begin flowing, and all the water in the entire loop must therefore flow
as well. It acts like a drive belt. Is it possible to break the circuit
and use a non-circular hydraulic system? Can we send compression waves
through the "water" in the "hose?" Sure! That's what the G-line does.
If we have a long hose with closed ends, we can send sound waves through
the water of the hose, although we cannot create DC as we can with the
closed circuit hose-loop. Single-wire systems are inherently AC systems.
They are analogous to sending acoustic energy along a fluid-filled
Because there is only one conductor in the G-line, the "E" part of the EM
wave must extend between successive lumps of net-charge which propagate
along the wire. The "voltage" on the transmission line extends outwards
as radial e-field flux, but rather than connecting with a coaxial shield
as it does in a normal cable, it curves around and connects with the
opposite flux-lines which extend from another place on the wire. The "M"
component of the wave acts like the magnetic field around any normal wire:
the magnetic flux lines act like circles which surround the wire. The
energy flows lengthwise along the wire as is commonly shown by Poynting's
vector (E x B).
__ | _____ | ___ \ | / \ | / \ | / \ | / | | | | | | | | | | | | | | | | | | wire ============ --------- =========== +++++++++ =========== | | | | | | | | | | | | | | | | | | / | \ / | \ ___/ | \_____/ | \___ fig. 4 The e-field of the "G-Line", extending between regions of moving chargeSo, here we have a one-wire transmission line based on electron density waves. Inside the metal of that single wire, the electrons wiggle back and forth while the EM wave propagates along in surrounding space at about the speed of light. It's almost like sound waves moving on a string, but electrons take the place of cellulose fibers, and the sound waves are replaced by transverse EM waves. It's the electromagnetic version of a "tin can telephone." But in this case, the energy is stored in the EM fields connected to the electrons, rather than being stored in the kinetic energy and potential energy of the string.
How does this relate to Tesla? Well, once we have the ability to send energy along a single wire, we should also have the ability to send energy along any conductor at all, as long as that conductor has a dielectric coating. Like this:
____ ___ ____ _____----- | ___--- --__ | -----_____ ------- |_______/ \_______| ------ -------_____ | \_ _/ | _____------ -----____| --_____---- |____----- fig. 5 "G-line" with a large conductive lumpAny large, metallic hunk could be stuck in series with the "G-line". Yes, there might be wave-reflections where the thin wire connects to the big metal hunk. But that's beside the point. With the above setup, we can send waves along the surface of a conductive object, while within the object itself the "electron sea" vibrates longitudinally. Hmmm. Where have I heard THAT before? I know. Nikola Tesla's "World System," in which he intended to transmit usable electrical energy to any receiver anywhere on the Earth.
In the above diagram, suppose the "hunk of conductor" is the entire planet
Earth! Suppose the "cone shaped" launchers are replaced with an elevated
sphere which supplies a "virtual ground" reference capacitance? Suppose
the frequency of the waves is below the UHF band in frequency? The
entire Earth will then behave as a "G-line" single wire transmission
metal _____ metal ball / \__ ball __ __ _/ \__ __ __ / \ |||| / \ |||| / \ \__/--==||||========-----\ /-----==========||||==----\__/ |||| \__ __/ |||| primary \_______/ 2nd "primary" coil conductive lump coil (the entire Earth!) fig. 5 Tesla's version of the "G-line"In his writings, Tesla was convinced that his devices did NOT use the same physics as Hertzian waves. He was right... and wrong. When radio- frequency energy propagates through empty space, the E and the M components are transverse, and the waves propagate at 90 degrees to both of them. However, when EM energy is sent along a cable, we also have electrons involved: the electron-sea within the metal wires. The electrons slosh back and forth in the cable while the EM waves flow along outside of the metal surfaces. Why is this important? Because the physics of a transmission line is the physics of the "near field" of a coil or capacitor, not the physics of freely-propagating "Hertzian" waves. When Tesla sent energy around the Earth, he was treating the Earth as an electrical cable. His waves were coupled to the charges within the surface of the Earth. He was not transmitting pure radio waves, even though the frequency of the wave-energy might be the same as any normal radio wave. Instead he was using a one-wire transmission system where the conductive Earth served as the wire. Tesla's technology used "near field" effects of coils, capacitors, and transmission lines, not the dipole antennas that Hertzian waves use, and in that sense his waves were "non-Hertzian."
But wait a minute. This stuff can only work if there is a dielectric
substance coating the Earth. Without that coating, the waves will not
follow the curve of the Earth, they will just fly out into space. The
atmosphere supplies this coating. And even better, there is a conductive
ionosphere which will act a lot like the "shield" of a coaxial cable and
force the waves to go around the Earth.
Tesla was using the ground as a transmission line. He was correct when he
insisted that he was producing longitudinal waves in the "natural medium."
He was correct in saying that the ground was not just a voltage reference.
In this case the "natural medium" is the population of mobile ions in the
dirt and oceans which cause the Earth act as a conductor. He was
converting the Earth's surface into a "G-line" conductor. Any
electrical device could intercept a portion of that energy, as long as
that device was connected to the ground and to an elevated metal object.
So, what was Tesla's big mistake? Initially he did not realize that the
Earth's atmosphere was critically important for his system to work. If
the Earth had acted like a metal ball hanging in a vacuum, then Tesla's
would not have worked. The waves would have travelled along the ground
and then shot out into space rather than curving around the Earth. His
system would have been like a "G-line" with a sharp bend in the middle:
except for a bit of diffraction, the waves ignore the bend and go right
off the cable and are lost.
Because of the "dielectric" effect of the atmosphere, and also because a
conductive ionosphere was present, Tesla's system was feasible. Yet any
scientist of the time would "correctly" see that Tesla's system totally
violates well-known theory. If Tesla had started out from known theory,
he would never
have pursued the path he did. Tesla actually started out with empirical
observations that the Earth resonated electromagnetically like a struck
bell. The atmosphere and the ionosphere made this so, but Tesla only knew
that it worked, and he really did not know why, at least at first.
Tesla's other big mistake was in thinking that his wireless
transmission system had nothing to do with "Hertzian" waves. In fact, the
waves in a coaxial transmission line are not much different than the waves
which fly off any dipole antenna connected to the end of that transmission
line. Whether it is ruled by "near field" or "far field" equations,
electromagnetism is electromagnetism.
Tesla's mistake was not really so big. Especially not a big mistake when
compared to those contemporary scientists who were absolutely certain that
the Earth *didn't* have any resonant frequencies, who *knew* that radio
waves would not travel around the curve of the Earth, and who dismissed
Tesla's wireless transmission system as crackpottery; as an unworkable
violation of known physics. When "Schumann" VLF earth-resonance was
rediscovered in the 1950s, nobody in the conventional sciences dared court
the embarassment of admitting that Tesla had been right all along.
Tesla is mostly a hero among the non-scientist "underground," while in
conventional circles he is still ridiculed for trying to distribute
electric power without using wires, or rather, by sending it through the
ground. Everyone (still) knows that this is
impossible, even in theory.
Geog Goubau, "Surface waves and their Application to Transmission Lines," Journal of Applied Physics, Volume 21, Nov. (1950)