17-05-2012, 10:55 AM
TESLA ON GLOBAL WIRELESS ENERGY TRANSMISSION FOR TELECOMMUNICATIONS AND OTHER PURPOSES
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Atmospheric Conduction Method
Energy Transmission By Means of a Spherical Conductor Transmission Line With an Upper Half-space Return Circuit.
Tesla's ideas about electrical conduction through the "natural media" fall into two categories: closed circuit and open circuit. [Henry Bradford]
In 1932 journalist John J. O’Neill conducted an interview with Tesla in which he talked about the difference between the wireless transmission of electric energy using what Mr. Bradford describes as either “closed circuit” or “open circuit” principles.
I also asked him if he is still at work on the project which he inaugurated in the '90's of transmitting power wirelessly anywhere on earth. He is at work on it, he said, and it could be put into operation. . . . He at that time announced two principles which could be used in this project. 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 is 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. "I do not use the plan involving the conductivity of the upper strata of the air," he said, "but I use the conductivity of the earth itself, and in this I need no wires to send electrical energy to any part of the globe." [“Tesla Cosmic Ray Motor May Transmit Power 'Round’ Earth,” Brooklyn Eagle, July 10, 1932.]
The closed circuit system consists of a large Tesla coil transmitter, an ionized path connecting the transmitter to the upper atmosphere, the upper atmosphere, a second ionized path connecting the upper atmosphere back down to a receiving location, and the receiver itself. The circuit back to the transmitter is completed through the earth. The upper atmosphere, like any low-pressure gas, is not an ohmic conductor, but will conduct electricity if broken down; i.e., ionized. The portion of the upper atmosphere between the transmitter and the receiver would then conduct current like a neon tube of planetary proportions. It would require a certain amount of energy to maintain the electrical discharge through it.
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, Leland I. Anderson, Editor, Twenty First Century Books, 1992, pp. 129-130.]
In operation, the electrical energy flowing through the air is characterized by its high voltage and low current, and through the earth by its high current and low voltage. For any given power level, the I2 R losses in the plasma transmission line is proportional to the value of the resistance ® of the ionized path between the two stations, and inversely proportional to the amount of current (I) flowing along this path. The voltage drop (E) across R is given by Ohm’s law, E = IR. There is an inverse relationship between voltage and current, so for any given load, increasing the transmission line voltage would reduce the current. For any given load, with a constant transmission-line resistance, lowering the current that flows through the transmission line would also reduce the voltage drop. This equates to greater transmission-line efficiency. In Tesla’s words,
. . . by such means as have been described practically any potential that is desired may be obtained, the currents through the air strata may be rendered very small, whereby the loss in the transmission may be reduced. [SYSTEM OF TRANSMISSION OF ELECTRICAL ENERGY, Sept. 2, 1897, U.S. Patent No. 645,576, Mar. 20, 1900.]
Tesla’s wireless transmitter-receiver station was designed to develop extremely high potentials on the elevated terminal in order to minimize the loss due to the plasma transmission line resistance. Another characteristic of the Tesla apparatus is that a high current flows in the conductor that connects the oscillator to the earth. Looking at an entire atmospheric conduction system, each of the transmitter-receiver stations serves, in a sense, as a lever and a fulcrum that converts the power flowing through the air and ground paths. [Kenneth L. and James F. Corum]
An independent power source is required at the receiving location to sustain the conducting path to the upper atmosphere. Both the transmitter and the receiver have to be capable of ionizing the upper atmosphere out to some distance, in much the same way that a corona discharge ionizes the air out to a radius at which its electric field falls below the breakdown value for air, or the leader in a lightning discharge ionizes the air ahead of the bolt.
Tesla described the ionization process like this:
For example, a conductor or terminal, to which impulses such as those here considered are supplied, but which is otherwise insulated in space and is remote from any conducting-bodies, is surrounded by a luminous flame-like brush or discharge often covering many hundreds or even as much as several thousands of square feet of surface, this striking phenomenon clearly attesting the high degree of conductivity which the atmosphere attains under the influence of the immense electrical stresses to which it is subjected. This influence is however, not confined to that portion of the atmosphere which is discernible by the eye as luminous and which, as has been the case in some instances actually observed, may fill the space within a spherical or cylindrical envelop of a diameter of sixty feet or more, but reaches out to far remote regions, the insulating qualities of the air being, as I have ascertained, still sensibly impaired at a distance many hundred times that through which the luminous discharge projects from the terminal and in all probability much farther. [SYSTEM OF TRANSMISSION OF ELECTRICAL ENERGY, Sept. 2, 1897, U.S. Patent No. 645,576, Mar. 20, 1900.]
Both wireless stations would be individually capable of ionizing the upper atmosphere in their vicinities out to distance that is based upon four physical parameters. Tesla identified these as the “electromotive force” of the transmitted impulses, the atmospheric density, the height of the elevated terminal above the ground, “and also, apparently, in slight measure, . . . the degree of moisture contained in the air.” By using a vertical ionizing beam the requirement for very tall towers is reduced.
I have also found it practicable to transmit notable amounts of energy through air strata not in direct contact with the transmitting and receiving terminals, but remote from them, the action of the impulses, in rendering conducting air of a density at which it normally behaves as an insulator, extending, as before remarked, to a considerable distance. . . . [Ibid.]
The upper troposphere between the transmitter and the receiver would become available as 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." [Nikola Tesla On His Work With Alternating Currents and Their Application to Wireless Telegraphy, Telephony, and Transmission of Power, 1992, p. 110.]
Tesla also spoke about instances in which the connection between the elevated terminals is, in part, by electrostatic induction.
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. [SYSTEM OF TRANSMISSION OF ELECTRICAL ENERGY, Sept. 2, 1897, U.S. Patent No. 645,576, Mar. 20, 1900.]
This means that a wholly conductive path between the transmitting and the receiving stations is not an absolute requirement. A portion the transmitter’s energy can be collected at the receiver by electrostatic induction alone. This also suggests that a flow of energy may occur between the two high-altitude ionized regions by means of electrostatic induction, that is to say, by so-called displacement current. Once the initial atmospheric connection is established by the means of true conduction (through the vertical ionized path), and displacement currents, each high-altitude ionized region might grow in size in the direction of its counterpart with the passage of time,
I have likewise observed that this region of decidedly-noticeable influence continuously enlarges as time goes on, and the discharge is allowed to pass not unlike a conflagration which slowly spreads, this being possibly due to the gradual electrification or ionization of the air or to the formation of less insulating gaseous compounds. [Ibid.]
To accomplish this would be a stupendous undertaking. It strikes me that Tesla’s concept of transmitting electric power wirelessly via electrical conduction through a closed circuit consisting of the earth and the atmosphere is not promising from a practical viewpoint. This is because of the enormous voltages needed to reach to useful distances from the transmitter through the atmosphere, and the power requirements for maintaining the air path in an ionized state.
Wireless power transmission by means of the atmospheric method appears to be feasible. It can be accomplished exactly as Tesla said it could without violating the known laws of physics. Perhaps it has not been adopted for economic reasons, and because certain basic engineering challenges that Tesla addressed while developing the system have not been revisited. Perhaps the point-to point atmospheric conduction method is simply impractical.
I [have] contemplated the possibility of transmitting . . . high tension currents [on the order of twenty million volts] over a narrow beam of radiant energy ionizing the air and rendering it, in measure, conductive. After preliminary laboratory experiments, I made tests on a large scale with the transmitter referred to [in Colorado Springs] and a beam of ultra-violet rays of great energy in an attempt to conduct the current to the high rarefied strata of the air and thus create an auroral such as might be utilized for illumination, especially of oceans at night. I found that there was some virtue in the principal but the results did not justify the hope of important practical applications. [The New Art of Projecting Concentrated Non-dispersive Energy Through Natural Media.]
Tesla spoke about the commercial establishment of a wireless system in which the transmitted energy is utilized in at least three different ways—high-frequency lighting, turning electric motors, and wireless telecommunications.
Wireless communications is not as demanding as the transmission of power. Tesla seems to have favoured carrier frequencies in the range of tens of kilohertz or so, which would be reasonable for transmission of information at a useful rate. He had in mind transmitters and receivers as those shown in his patent drawings, communicating through the earth via current from the ground terminal of the transmitter and the partially or wholly ionized path described above. This raises the question of whether the current from the ground terminal of a Tesla transmitter, which definitely would exist, would have a range comparable to or greater than that of a radio wave from a radio transmitter of the same power and frequency, and the induced earth current that would accompany it.
The principal difference between Tesla’s system, either closed or open circuit, and open circuit low frequency radio systems is that a radio transmitter is designed primarily to emit energy in the form of electromagnetic radiation from its antenna, whereas the Tesla communications transmitter is designed primarily to inject an electrical current into the earth at its ground terminal. The mode of propagation for both systems appears to me to be the same; i.e., earth currents and surface charge coupled to a vertical electric field in the Earth-ionosphere cavity.