The wireless method Tesla planned to use at Wardenclyffe involves an electric current flowing through the earth between a Tesla coil transmitter and a Tesla coil receiver. Both the transmitter and receiver would be built the same way, with a powerful Tesla coil located inside each of the tower structures. In the case of Wardenclyffe the second plant was to be constructed on the southern coast of England, possibly in Cornwall.
The atmospheric conduction method depends upon the passage of electrical current through both the earth and the atmosphere.
"The earth is 4,000 miles
radius. Around this conducting earth is
an atmosphere. The earth is a
conductor; the atmosphere above is a conductor, only there is a little stratum
between the conducting atmosphere and the conducting earth which is insulating.
. . . Now, you realize right away that if you set up differences of potential
at one point, say, you will create in the media corresponding fluctuations of
potential. But, since the distance from
the earth's surface to the conducting atmosphere is minute, as compared with
the distance of the receiver at 4,000 miles, say, you can readily see that the
energy cannot travel along this curve and get there, but will be immediately
transformed into conduction currents, and these currents will travel like
currents over a wire with a return. The
energy will be recovered in the circuit, not by a beam that passes along this
curve and is reflected and absorbed, . . . but it will travel by conduction and
will be recovered in this way. [Nikola Tesla On His Work With Alternating
Currents and Their Application to Wireless Telegraphy, Telephony, and
Transmission of Power, pp. 129-130]
The electric current through the earth is balanced by an equivalent electrical displacement of the opposite sign through the space above it. This displacement can be achieved by means of electrical conduction through the atmosphere without violating any of the known laws of physics. With energy transmission by true electrical conduction, a very high voltage on the order of 15 million volts is needed on both of the elevated terminals to break down the insulating air around and above each plant. The ionization of the atmosphere directly above the elevated terminals is facilitated by a vertical ionizing beam of ultraviolet radiation that leads to the formation of a plasma high-voltage electrical transmission line. The upper troposphere between the transmitter and the receiver is available for a conductor by inducing the plasma state within that region. This is the “aurora” effect described by Tesla in the 1916 interview.
"I have constructed and patented a
form of apparatus which, with a moderate elevation of a few hundred feet, can
break the air stratum down. You will
then see something like an aurora borealis across the sky, and the energy will
go to the distant place." [NTAC, p. 110]
The end result is a flow of true conduction currents between the two elevated terminals by a path up to and through the troposphere, and back down to the other facility. To learn more about this mode of operation read the paper "Nikola Tesla On Wireless Energy Transmission, with additional comments by Henry Bradford and Gary Peterson" located at http://www.teslaradio.com/pages/tesla.htm .
In addition to the atmospheric-conduction method the Tesla coil transmitter design is also adaptable to another method that Tesla had for wireless transmission called "earth resonance." Comparing Tesla's patents covering his wireless system using the earth resonance method and those covering the atmospheric conduction method reveals that both the basic transmitting and receiving apparatus are identical. Both consist of large Tesla coils connected to the earth and to high-voltage elevated terminals. (It is important to note that a single earth-resonance Tesla coil transmitter can be made to perform exactly as intended without any additional stations being present. In this case the earth itself overrides the requirement that one or more additional stations be placed into operation.)
The differences between the two methods are in the potential that is required at the TC transmitter's elevated terminal, and also in the operating frequency. For atmospheric conduction about 15 million volts is needed. For earth resonance the elevated terminal has to be charged up to about 100 million volts! As for frequency, the usable base frequency spectrum is about the same for both types of system, say 1,000 to 35,000 cycles per second (1-35 kHz). An atmospheric conduction system can operate at any arbitrarily selected frequency in this region. With an earth resonance system it is compulsory that it operate on some harmonic of the fundamental earth-resonance frequency, reported by Tesla as being about 12 Hz.
By the way, there is a misconception among many Tesla researchers that he intended to transmit electric power through the Schumann or earth-ionosphere cavity. While Tesla definitely spoke of exciting a terrestrial resonance mode, he was not talking about exciting a Schumann resonance. The terrestrial resonance mode that he apparently excited in 1899 at Colorado Springs is referred to by some as an "earth resonance mode," which are different from the Schumann resonance modes. Also remember that Tesla made a distinction between electrical energy transmission by atmospheric conduction and electrical energy transmission using earth resonance principles.
". . . In one the ionizing of the
upper air would make it as good a conductor of electricity as a metal. In the
other the power would be transmitted by creating "standing waves" in
the earth by charging the earth with a giant electrical oscillator that would
make the earth vibrate electrically in the same way a bell vibrates mechanically
when it is struck with a hammer. . . ." ["Tesla Cosmic Ray Motor May
Transmit Power 'Round' Earth," Brooklyn Eagle, July 10, 1932, John J. A.
O'Neill]
One final note, the earth possesses a naturally existing negative charge with respect to the conducting region of the atmosphere beginning at an elevation of about 50 kilometers. The potential difference between the earth and this region is on the order of 400,000 volts. Near the earth's surface there is a ubiquitous downward directed E-field of about 100 V/m. In LIGHTNING PROTECTOR, May 6, 1916, U.S. Patent 1,266,175, May 14, 1918 Tesla referred to this charge as the “electric niveau” or electric level.
"A point of great importance would
be first to know what is the capacity of the earth? and what charge does it contain if electrified? Though we have no positive evidence of a
charged body existing in space without other oppositely electrified bodies
being near, there is a fair probability that the earth is such a body, for by
whatever process it was separated from other bodies—and this is the accepted
view of its origin—it must have retained a charge, as occurs in all processes
of mechanical separation. If it be a
charged body insulated in space its capacity should be extremely small, less
than one-thousandth of a farad. But the
upper strata of the air are conducting, and so, perhaps, is the medium in free
space beyond the atmosphere, and these may contain an opposite charge. Then the capacity might be incomparably
greater. In any case it is of the
greatest importance to get an idea of what quantity of electricity the earth
contains. It is difficult to say
whether we shall ever acquire this necessary knowledge, but there is hope that
we may, and that is, by means of electrical resonance. If ever we can ascertain at what period the
earth's charge, when disturbed, oscillates with respect to an oppositely
electrified system or known circuit, we shall know a fact possibly of the
greatest importance to the welfare of the human race. I propose to seek for the period by means of an electrical
oscillator, or a source of alternating electric currents. . . . [“On Light and Other High Frequency
Phenomena,” Franklin Institute, Philadelphia, February 1893, and National
Electric Light Association, St. Louis, March 1893.]
Tesla coil earth resonance transmitters create a local disturbance in the earth’s charge that manifests itself as an annular deviation in the strength of the background electric field. This disturbance moves away from the transmitter and diminishes in intensity as the distance from the transmitter increases. A sufficiently powerful transmitter produces a field distortion that propagates to the antipode at which point the energy is reflected back towards its point of origin. The transmission of electrical energy across the entire globe and its reflection all the way back to its source is the basis of Tesla's earth resonance method. While the atmospheric conduction method requires that both transmitting and receiving apparatus be placed into operation, a properly tuned and sufficiently powerful earth resonance transmitter, on the other hand, can be made to operate exactly as intended without any man-made Tesla coil receivers being activated. The earth itself fulfills the important requirement that a synchronized receiver be present.
To conclude this section, the two fundamental principles behind the operation of Tesla's system are:
1. Low frequency alternating current can be transmitted through the earth with low resistive loss due to the fact that the resistance between antipodes of the earth is considerably less than 1 ohm.
2. Low frequency high voltage alternating current can be transmitted through the atmosphere with low loss. The electrical displacement takes place by a) electrostatic induction, b) electrical conduction, or a combination of these two.
http://www.teslaradio.com/pages/wireless_transmission_theory.htm
One question to be answered about Tesla’s wireless system is whether the energy is being carried from the transmitter to the receiver by ordinary radio waves or if some other mechanism is involved. We are speaking here of scaled-down versions of Tesla’s wireless system such might be assembled by the typical Tesla coil experimenter. The operational power levels involved are assumed to be insufficient to excite earth resonance or result in massive atmospheric ionization in the vicinity of the oscillators. No provisions are made for the generation of vertical ionizing beams originating at the elevated terminals and projecting up to an elevation of say 8 km where conductivity can more easily be imparted to the air.
Regarding the transmission of electrical energy from a Tesla coil transmitter to a Tesla coil receiver, seven possible mechanisms have been identified that are available according to present electromagnetic field theory. The first three are far-field electromagnetic radiation or ordinary radio waves, mutual induction, and mutual capacitance. The fourth is the Goubau or G-line waveguide transmission line model presently being advanced by William Beaty. There may be aspects of the physics behind the G-line that are not fully understood. The fifth is an alternative mechanism involving ordinary radio waves produced in the far-field zone as a result of ground currents propagating to a great distance from operating Tesla coil transmitters. Henry Bradford is presently developing this hypothesis. The sixth mechanism is the propagation of an ion-acoustic wave in the intervening space between the two elevated terminals. The seventh mechanism is the modulation of natural plasma that exists because of the electrical potential gradient between the earth’s surface and the conducting region of the atmosphere beginning at about 50 kilometers.
An eighth proposed mechanism considers the transmitter and receiver as being “self-referencing” by means of virtual electrical grounds, a theoretical concept developed by Eric Dollard and others in the 1980s.
The ninth proposed mechanism is what might be called "electrostatic induction."
Far-field electromagnetic radiation or ordinary radio
waves
Ordinary radio waves can be excluded because field measurements taken on actual Tesla coil transmitters demonstrate that when these devices are in a higher state of refinement they are very inefficient in terms of the production of electromagnetic radiation. There is insufficient signal strength to account for the amount of energy received in the far-field zone.
Mutual induction
Energy transmission by "mutual induction" can also be excluded because the magnetic field density falls off too rapidly to account for amount of energy received in the far-field zone.
Mutual capacitance or displacement current
The elevated terminal of a Tesla-coil transmitter functions as a capacitor plate. Opposite to this plate is every other electrically conducting body to which it is connected, including the earth and, in some cases, the receiving transformer's elevated terminal. The transmitter's elevated terminal serves two purposes: first, it acts as a charge reservoir in relation to the earth's surface in the immediate vicinity of the transmitter; second, it is one of two electrodes, the other electrode being the receiving facility's elevated terminal. The transfer of energy between a Tesla coil transmitter and the requisite Tesla coil receiving transformer is by electrical conduction between the two respective ground terminals. For distances up to about 1/2 wavelength the propagation of energy between the respective elevated terminals is the result of displacement currents, exactly like the transfer of electrical energy between the plates of a conventional capacitor in an AC circuit. This explanation is fine for distances up to about 1/2 wavelength, but in general the electric field intensity follows an inverse square, and diminishes rapidly with distance. Therefore, energy transmission by "mutual capacitance" can be excluded because when the two elevated terminals are separated by more than one-half of a wavelength of the applied current they are, for practical purposes, electrically decoupled.
The Goubau or G-line waveguide transmission-line model
This explanation is a strong candidate. A Tesla coil transmitter consisting of a high voltage, pulse-driven, end-loaded resonator launches a transmission-line wave, similar to the Zenneck Surface Wave, in the form of earth currents and a charge-coupled electromagnetic field.
This explanation is also in the running. The basic idea is that the earth currents and charge-coupled electromagnetic field associated with Tesla coil transmissions gradually decouple from the associated charge carriers and become ordinary radio waves as a function of the distance from the transmitter. Mr. Bradford states, “I do not believe that the theory for it has been worked out, but in principle it is a straightforward application of electromagnetic theory.”
Electrostatic or magneto-hydrodynamic plasma wave model
In operation a radio-frequency current is applied to each of
the two resonators creating, at each location, an oscillating magnetic field. In turn, the oscillating magnetic field
induces an oscillating electric field.
The oscillating electromagnetic field creates a weak to highly ionized
plasma in the vicinity of each resonator, depending on the amount of power
applied to the oscillation transformer primary. The volume of the ionized region is proportional to the peak
energy of the oscillation. If the currents in the two resonators have a
180deg phase relationship with each other, then conditions are favorable for
interconnection of their respective magnetic fields. In addition to the inductively coupled discharge created plasma,
conditions also exist for the creation of capacitively coupled discharge plasma
between the two respective elevated terminals.
These would be either electrostatic waves or more likely magneto-hydrodynamic waves, assuming the
presence of inter-connected magnetic field lines. The
transfer of energy between a Tesla coil transmitter and the requisite Tesla
coil receiving transformer is by electrical conduction through the earth
between the two respective ground terminals, and also through artificially
created weakly ionized plasma between the two elevated terminals. For a
high-power system, coupling between the elevated terminals is by electrical
conduction through highly ionized plasma. The two electrodes act as high
voltage discharge terminals for the formation of capacitively coupled discharge
plasma with the electrical interconnection taking place through the upper level
atmosphere. The ionization of the denser atmosphere
directly above the elevated terminals is facilitated by the use of an ionizing
beam of ultraviolet light to form what might be called a high-voltage plasma
transmission line.
Modulation of naturally existing plasma model
The entire earth
possesses a naturally existing negative charge or DC electrostatic potential
with respect to the conducting region of the atmosphere beginning at an
elevation of about 50 kilometers. The potential difference between the
earth and this region is on the order of 400,000 volts. Near the earth's
surface there is a ubiquitous downward directed E-field of about 100 V/m.
In operation, a grounded Tesla coil transmitter creates a local disturbance in
this charge. The disturbance manifests itself as an annular distortion of
the background electric field around the transmitters ground terminal. At
a point in time when a measurement of the e-field component of the EM field at
the ground terminal should show zero volts above the background potential,
other measurements should show it rising in intensity until a point 1/4
wavelength (1/4 λ) away from the ground terminal is reached (axial
projection). From there the e-field should diminish in intensity until,
at 1/2 wavelength from the terminal, it again shows zero. At a
measurement point approximately one wavelength away from the ground terminal,
an induced e-field once again should begin to emerge above the average
background field level, again increasing in intensity until a second maxim is
reached at 1 1/4 wavelengths away from the oscillator. It is possible
that measurements would reveal a zero crossing to a relative potential of the
opposite sign. With a sufficiently
powerful transmitter this phenomenon would be expected to repeat itself over
and over until the antipode is reached, at which point reflection would take
place and the transmitted energy would begin to travel back to its point of
origin in the reverse direction. With the proper selection of operating
frequency constructive interference with the outgoing wave will take place.
Virtual ground model
The transmitter and receiver are viewed as being “self-referencing” through the establishment of virtual electrical grounds comprised by the two elevated terminals. The system would use earth resonance to circumvent the Newtonian law of action and reaction. “In this arrangement energy is continuously bounced back and forth between the earth and the reflecting capacitance at a rate tuned to a natural rate of the earth.” [Eric Dollard] Alternatively, circumvention of Newton’s Third Law would be due to electrodynamic force interactions between heavy ions and electrons, known as the anomalous cathode reaction force. [P.N. and A.N. Correa]
"Electrostatic induction"
For distances beyond about 1/2 wavelength the propagation of energy between the respective elevated terminals is the result of what might be called “electrostatic induction” somewhat like the transfer of electrical energy between the two plates of a capacitor in an AC circuit. This is a proposed mechanism by which the two distant elevated terminals might be electrically coupled together in a manner similar to mutual capacitance, but at distances greatly exceeding 1/2 wavelength. Tesla used the term electrostatic induction to describe the behavior capacitors, or more generally, the electrical coupling of two or more conducting surfaces that are separated by one form or another of dielectric. This term appears in Tesla’s “SYSTEM OF TRANSMISSION OF ELECTRICAL ENERGY (U.S. Patent No. 645,576, dated March 20, 1900) and elsewhere.
“In some cases when small amounts of energy are required the high elevation of the terminals, and more particularly of the receiving-terminal D' may not be necessary, since, especially when the frequency of the currents is very high, a sufficient amount of energy may be collected at that terminal by electrostatic induction from the upper air strata, which are rendered conducting by the active terminal of the transmitter or through which the currents from the same are conveyed.”
Notes:
In the cases of mutual capacitance, the Goubau-line model, the two plasma wave models, the virtual ground model, and electrostatic induction it is an absolute requirement that both the Tesla coil transmitter and the terrestrial Tesla coil receiver be very well connected to the earth’s subsurface, allowing them to be coupled together by electrical conduction through the earth between their ground terminals.
It is quite conceivable that it will be found the best explanation for the long-distance transmission of electrical energy between a Tesla transmitter and receiver is a combination of two or more of the above-proposed mechanisms.