The Tesla Coil
Nikola Tesla, in his investigation into high-frequency electricity phenomena, needed a way to go beyond the limitations of the iron-coil transformer to generate higher frequency radio waves. His inspiration lead him to invent a special transformer, without the iron-core, which allowed the secondary coil to be free to oscillate or "electrically vibrate" into higher and higher frequencies. The infamous Tesla Coil (invented 1891) is an air-core resonating transformer became the forerunner of the radio-frequency coil and allowed the "Radio Age" to take one of it's first formative steps.
Tesla coils as spark radio transmitters have been phased out since the late 1950's, but have been miniaturized and today, form the heart of every television, radio and VCR.
You can think of the coil as a string on a musical instrument. If you pluck the string then it will vibrate with a certain frequency, which is based on the length of the string. This is a "resonant frequency". After all, isn't music is based on the science of vibrations?
Now a basic principle of electrical engineering is that the ground is an electrical sinkhole, where energy returns to. But what would happen if the ground was suddenly reversed and became a source of energy? When electricity is "sunk" into the ground it travels much like a ripple in a pool of water, traveling through the earth and bouncing back to the point of origin. By correctly timing the discharge of electricity from a Tesla coil, you can continue amplifying your electric ripple until it builds up to great strength. (3)
(3) "Nikola Tesla - the Tesla Coil", teslaenergy.org
Nikola Tesla was a multi-disciplinary genius. His discovery of the rotating magnetic field in 1882 led to a series of US Patents in 1888, which gave us the AC electric power system still in use today. This one achievement earned him the honor of being called “The Man Who Invented the 20th Century”.
His research went way beyond what has found its way into everyday use. He is the recognized inventor of the brushless AC induction motor, radio, remote control by radio, super-conductivity, fluorescent lighting, the bladeless turbine engine and pump, the capacitor discharge ignition system for automobile engines, the mechanical oscillator, and dozens of other inventions. But he also discovered that useful energy could be extracted from the heat of the ambient air, and that electric power in the form of Radiant Energy could be broadcast to everyone in the world through the ground. (1)
Tesla also introduced a very important energy concept, high frequency oscillations, to allow our technology to be in harmony with nature and to realize new, undiscovered, limitless resources of energy. With over 700 patents, Tesla is considered to be the father of our modern technological age and one of the greatest scientific minds that has ever lived! The electronics produced by Tesla’s inventive mind transformed the world we now enjoy. Furthermore, Tesla’s mind worked unceasingly to open a new window of high-frequency electronic science that was, beyond a future dependency on fossil fuel technologies. He warned that this dependency would eventually turn on us, like a Frankenstein monster, poisoning and suffocating our planet; he offered the world a pollution-free wireless broadcast of power. Tesla often advised that in order to discover the secrets of nature and the universe we should think in terms of frequency, vibration, and energy. (2)
(1) abstracted from article "Nikola Tesla", freeenergy.ws
(2) abstracted from article "Nikola Tesla - High Frequency Currents" on teslaenergy.org