The Tesla coil: A Frankenstein folly or a brilliant Nikola Tesla creation?
A mini Tesla coil using a DC voltage input8
The electrical engineering faculty members at UTeM Malaysia, put together a pretty neat design for a Tesla coil with better mobility, being less bulky than typical designs. Their goal was to generate a high frequency current with a medium voltage, that is, 2.5kV on the secondary with an unusual 24VDC at the primary input side instead of an AC voltage as is typical with most designs.
The proposed mini Tesla coil uses all the same components as a traditional Tesla coil such as the toroid, primary and secondary coils, spark gap and capacitor. On big difference is that the mini-design does not use a rotary of sphere gap, but instead a contactor of a relay since conventional spark gaps would not work with a 24 VDC input.
The 24 VDC is not enough to fire the gap across the relay contactor since a one millimeter gap needs 3 kV to generate an arc. Instead, the arc is created by opening and closing the gap very quickly. During the opening and closing of the relay, the 24V will charge the tank capacitor which will in turn transfer energy to the primary of the transformer.
Guiding high voltage arcs in the Tesla coil
Finally, let’s take a look at a technique guiding the high voltage arcs of the Tesla coil by using laser-induced plasma filaments in air5.
A terawatt femtosecond laser was used to guide high-voltage arcs in the air using plasma filaments. A high-voltage electrode, set at the top of a Tesla coil voltage elevator, emanates arcs to a grounded node.
Extremely short, pulsed laser beams, having energy in the mJ region, have non-linear propagation in air. Long plasma filaments, also known as Birkeland currents (Much of Nikola Tesla’s research and experimentation was in the plasma region of guided energy and power) having electron density of 1016 – 1018 cm-3 are able to be generated due to dynamic competition between the non-linear Kerr self-focusing (which eventually collapses the beam) and plasma de-focusing (which tends to halt the collapse of a beam). The laser ionizes the air and causes this effect.
The plasma filaments in this experiment5 with radii of 200 um can exist over relatively long distances carrying high-voltage energy across the air gap. The high voltage Tesla coil in the experiment produced bursts of pulses up to 350 kV at tens of us rise times. By modifying the Tesla coil to give it the capability of triggering the discharge pulses with sub-nanosecond jitter, perfectly straight laser-guided arcs were generated between the electrodes.
Figure 7: Diagram of coupling device for creation of a plasma antenna (Courtesy of reference 10)
Virtual plasma antennas10 in the RF region might be a practical application using this technique. This phenomenon gives passive radar a tremendous advantage in using a wideband diverse pulse train that improves detection probability of the radar with stealthy fluctuated targets which traditional antennas have difficulty in generating. Plasma antennas vs. copper antennas have great success with wideband frequencies enabling them to transmit a more diverse radar waveform.
Other practical uses of Tesla coil technology
When Tesla created his Tesla coil, he actually made an antenna out of the high-voltage secondary which acted as a very powerful radio transmitter. A great many early radios used Tesla coils in their transmission antennas. After creating the Tesla coil, the inventor used it to investigate and experiment with fluorescence, biological effects, x-rays, wireless power, radio and ultimately the Earth’s electromagnetic nature related to the atmosphere.
Tesla coil circuits were used in early wireless telegraphy in spark gap radio transmitters until the 1920s.
The Tesla coil technology was used in an early 20th century, but now obsolete, medical therapy----electrotherapy. A violet ray was the old medical appliance that would apply a high-voltage, low current, high-frequency current to the human body. This technique was said to cure many ailments. Unfortunately, this was a misguided use of Tesla’s technology which caused more problems to people than it cured.
An early particle accelerator design in 1928 by Rolf Wideroe, generated its high voltage using a Tesla coil. Even the flyback transformer is a form of Tesla coil which was first used to generate the high voltage in a TV tube.
Please share with our readers your Tesla coil experiments, experiences and designs.
1 Tesla coil theory on Terry Blake home page
2 Richie’s Tesla coil web page
3 Tesla coil design web page
4 The Zeus Tesla coil on the Hazardous Physics webpage
5 TRIGGERING AND GUIDING OF HIGH-VOLTAGE TESLA COIL DISCHARGES BY FEMTOSECOND LASER-INDUCED PLASMA FILAMENTS IN AIR, Yohann Brelet, Aurélien Houard, Bernard Prade, Jérôme Carbonnel, Yves-Bernard André and André Mysyrowicz
6 BUILDING THE WORLD'S LARGEST TESLA COIL HISTORY AND THEORY, Gary L. Johnson 1990
7 SOLID STATE TESLA COIL, Dr. Gary L. Johnson 2001
8 A Simple Design of a Mini Tesla Coil With DC Voltage Input, M. B. Farriz, A. Din, A.A. Rahman, M.S. Yahaya, J.M. Herman
9 Solid State Tesla Coils and Their Uses, Sean Soleyman submitted in 2012 as a research project for his Master of Science degree at U of C Berkeley, CA
10 Reconfigurable Plasma Antenna Produced in Air by Laser-induced Filaments: Passive Radar
Application, Mostafa Alshershby and Jingquan Lin
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