Nikola Tesla was one of the first minds to envision a wireless future. In the year 1900, he claimed that there would be precise wireless transmission of signals that would be received by devices no larger than a watch. He's of course describing what we now know as radiowaves, the foundation of how our modern connected electronics work.
Tesla, in fact, believed in this idea of wireless communication and energy transfer so much that he started constructing a transmitting station in New York to prove his point. Called Teslas' 'World System of Wireless', it was unfortunately never completed due to Tesla running out of money.
With that said, we still have the plans from Tesla for this wireless technology so we can take a closer look at its design and how it would've worked.
Tesla's idea of wireless transmission
After Tesla had already made a name for himself in the scientific and electrical realm, he started opening up laboratories in New York City. In 1888, he was conducting experiments at one of the laboratories specifically focused on alternating current.
Through these experiments and tests, he was able to develop a method of converting direct current and even low-frequency alternating currents into high-frequency currents.
It was during the development of these transformers and alternators that he realized alternating current circuits can still function if they aren't fully 'complete'. Rather, that the current can still flow along just one wire from one grounded terminal to a second grounded terminal and the circuit would still work. Tesla discovered that when the source of the current was of high enough frequency, he could essentially use the ground as a part of the circuit.
If the grounded terminal had a high enough voltage grounded, and a wire was connected to the other terminal, the current could be drawn along the wire by the capacitance of a conducting body connected to the other end of it.
The capacitance of say, a light bulb, was enough to draw current from the circuit to light it up, which is similar to how radio transmitters work.
Along the same train of thought, Tesla came up with a brilliant wireless transmission idea. It was to use the earth as the conductor for transmitting currents. As described in a lecture from Tesla in 1893, the device would connect a generator between the ground and a spherical conductor raised into the air.
The electromagnetic frequencies resulting from the generator in this setup would ensure that the alternating current was of opposite sign from the earth. Tesla consequentially believed that the ground—the earth—could be set into a state of oscillations with little dissipation of energy.
Through this discovery of the ground's ability to be utilized as a transmission medium, Tesla developed a plan to send high-frequency currents through the ground that would propagate anywhere around the globe, being received by a resonant receiver.
The conductivity of soil and water is much smaller than metals, but the resistance between the transmitter ground terminal and a given distant point would be very small, due to the large cross-sectional area of the Earth.
The formula for the transmitter current that would wirelessly propagate throughout the earth looks like this:
I = 2πfCV
I is current in amps, f is the frequency in hertz, C is the self-capacitance of the transmitter sphere and Earth in farads, and V is the voltage between the sphere and the ground.
Tesla went on to utilize this equation to build his station on Long Island, where he first started testing the idea. A generator was used to produce 10 million volts at 700 amps at 10 kilohertz. The high voltage was necessary to produce a strong enough current for his wireless transmission idea, so he constantly pushed the limit of what he could generate with his machines.
By this time, Tesla had a semi-working prototype and he began patenting his wireless transmission and reception technology around 1897. His patent was granted after review in 1900, with one of the diagrams of the device shown below.
While the receiver and transmitter parts of Tesla's invention were clear in his patent filing, many of the functioning principles and inner workings of the device were not explained in great detail. He theorized that if he was able to transmit a high enough voltage and current that he would be able to transmit useful levels of wireless energy anywhere in the world.
The machine was also capable of producing such high amounts of electricity that they could theoretically have been used to create man-made aurora borealis, or northern lights.
Teslas' oscillating devices
Tesla's generators, transmitters, and oscillation devices were groundbreaking for their time. Aside from simply electronic electricity transmission, his kinetic oscillation devices were also equally as interesting. By leveraging oscillations in the ground and in structures Tesla believed that he could transmit energy as kinetic waves through matter, which could then be translated back into electrical energy on the receiving side.
To achieve this, he built a steam-powered oscillation device that could have its frequencies manipulated. When the frequency of the oscillation device matched the resonant frequency of the receiver, the mechanical motion would be transformed back into usable electrical energy.
Tesla was actually able to get this technology working too. He built his first mechanical oscillator in 1897 and in 1898, he was able to oscillate his laboratory with just a small generator. Located in New York City with close proximity to neighbors, the oscillations and shakings in the building were enough that neighbors eventually called the police, fearing something very bad was happening.
It wasn't until 1912 that the first article about Tesla's resonator device was published.
Tesla being somewhat of a fringe brilliant mind would take his small vibration device and test it on different structures in the cities. According to The World Today Magazine from 1912,
"He put his little vibrator in his coat-pocket and went out to hunt a half-erected steel building. Down in the Wall Street district, he found one, ten stories of steel framework without a brick or a stone laid around it. He clamped the vibrator to one of the beams, and fussed with the adjustment until he got it. Tesla said finally the structure began to creak and weave and the steel-workers came to the ground panic-stricken, believing that there had been an earthquake. Police was called out. Tesla put the vibrator in his pocket and went away. Ten minutes more and he could have laid the building in the street. And, with the same vibrator, he could have dropped the Brooklyn Bridge into the East River in less than an hour."
That reference creates quite the devious and interesting picture of Tesla going throughout New York City testing his various inventions. Tesla did take this technology further, even into fields that you might not be aware of.
He developed a way to utilize the oscillations created by his steam generator in order to analyze the subsurface conditions of the Earth. By generating seismic waves with the oscillator, the reflected waves could give Tesla and other researchers information about the layers of rock below.
In essence, this technology was the first way that geologists were able to see into the Earth without digging holes or taking bore samples. In fact, the principle of using an oscillation generator that creates seismic waves to study subsurface conditions is still used by seismologists today.
Today, the equipment is much more high tech of course, but it still owes a lot to Tesla's invention from over a century ago.