research

Hunter R. J. Stevenson

AP English Literature Period 2

Mr. Frederic White

20 November 2015

The Audio Modulated Tesla Coil

Senior Project Research Paper

Introduction

Many people nowadays have heard the term “Tesla Coil” thanks to sci-fi movies and viral Youtube videos. These often showcase the fascinating ability of Tesla Coils to amaze and inspire by producing music solely with electrical sparks. But what is a Tesla Coil, and how does it work? More importantly, how can I make one that plays music? My senior project will be to explore these questions by constructing an audio modulated Tesla Coil, or “Musical Tesla Coil.” First, I will research the history of the Tesla Coil and its inventor, Nikola Tesla, to find how the Tesla Coil came to be. I will then research the original purpose and application of the Tesla Coil and how this has translated to the modern day. I will also need to research the different types of Tesla Coil to find which one is most suited for audio modulation. I will research the different components and construction of the Tesla Coil and how this relates to audio modulation. Finally, I will find possible sources of inefficiencies and how to minimize them. The project will culminate in constructing an audio modulated Tesla Coil and performing songs with it.

Research

Tesla was a public figure of great interest, working on the bleeding edge of science and exciting the imaginations of the people. His most famous contribution to electrical science was his work in alternating electrical currents, however, he did much more than this (Electrical Review). By the time of his death, he had patents in 23 countries, including 112 U.S. patents, 30 German patents, 14 Austrian patents, 13 French patents, 11 Italian patents, and many more (Jadwani). He also invented the induction motor and the three phase power system that is still in use today several years before his work on the Tesla Coil. Tesla’s contributions to science have truly changed the course of human history (Choudhury).

Tesla designed the first Tesla Coil in 1891. It was what is now classified as a Spark Gap Tesla Coil (SGTC) and consisted of a “primary” circuit that was charged and discharged into the “secondary” circuit across a small “spark gap” (Soleyman). In this way, each cycle added energy to the last and larger charges than seen in previous transformers could be accrued (Dunn). Seeing a great potential in this system, Tesla desired to upscale his device in order to accomplish several goals. These were: to create a more powerful radio transmitter than previously capable, develop the means for singling out transmitted energy for specific uses, and discover the laws of how electrical currents move through the earth (Tesla 1904). He built his laboratory on a plateau in Colorado Springs, where the air was dry and static electricity was in abundance, for this purpose (Choudhury). This laboratory consisted of an 80-foot wooden tower with a 200-foot mast on top. This mast had a copper ball on the end and was used as his transmitting antenna (Jadwani). Eventually, Tesla’s goals were realized when one day a large electric storm came in, and by measuring fluctuations in the electric fields during lightning strikes Tesla observed stationary waves propagating through the atmosphere (Tesla 1904). Tesla was then persuaded that in building a large enough Tesla Coil he could ionize the entire atmosphere, allowing it to conduct electricity. This, unfortunately, proved to be a fruitless endeavor (Choudhury). However, Guglielmo Marconi, the inventor of long distance radio transmission, borrowed heavily from Tesla’s work when building the first radio transmitter (Jadwani).

Tesla had big plans for his new coil. In general, Tesla envisioned his invention being capable of vastly improving three areas of interest: Dissemination of intelligence, transportation, and transmission of power (Petković). More specifically, Tesla believed that there was a significant military application in his work, which would bring to pass the much-needed peace of the time. His Tesla Coils could be used to  power and control ships and torpedoes at a distance (Tesla 1905). Coils could also transmit messages and information instantaneously across vast distances. One transmitter coil could be used to power many other diverse devices, such as precisely synchronized clocks, geolocation devices, airplanes, and lightbulbs (Tesla 1904). In terms of practical use, however, the latter of these devices sparked the most interest. Tesla conducted numerous experiments with powering fluorescent and incandescent lamps at a distance, as well as using the coil’s arcs themselves as high-frequency arc lighting (Connick). He realized that this would be one of the Tesla Coil’s chief uses as electric lighting was just coming into popular use (Tesla 1904). This research led him to develop the first high-efficiency high-frequency lighting ballasts, which paved the way to the modern Metal Halide Lamps (Connick).

Wireless power is a highly sought after technology still today. It makes devices more convenient by eliminating the need for a power cord or replacement batteries, which is also good for the environment (Makaa). Wireless power also does away with the dependence on power lines, substations, and towers which dot the face of the Earth (Mohammed). It reduces system costs by being able to power multiple devices simultaneously. Also, unmanned planes and robots can be employed for research and run for months at a time in places where wires cannot be involved (Makaa). Today, the most notable use of Tesla Coils themselves is for entertainment and educational displays. However, the concepts applied in the Tesla Coil are essential to many modern technologies (Choudhury). The first applications of the Tesla Coil could be seen in early flyback transformers and the ignition system in combustion engines (Connick). Induction coils have also been used in medical x-ray devices and particle accelerators, in addition to electrical stage shows and entertainment (Choudhury). While the technology needed to realize these ideas were not available to Tesla in his time, the principles applied survived the test of time and saw fruition in modern times (Ercegovac).

There are currently three main types of Tesla Coil. These are the Spark Gap (SGTC), Solid State (SSTC), and Dual Resonant Solid State (DRSSTC) Tesla Coils (Connick). In an SGTC, the charge is built in cycles, meaning that the primary coil is first charged, then discharged across a gap into the secondary coil which holds the charge as the primary is recharged and then discharged again. When the charge in the secondary reaches a certain level, it will then discharge and produce the visible spark (Soleyman). An SSTC is very different, in that the charge in the primary is continuously being discharged into the secondary and is controlled by solid state devices (Dunn). While the SGTC is the simplest design, it is less suitable for audio manipulation and the spark gap can produce intense harmful UV light. Because of this, the SSTC is the most favorable and most common design for use in audio manipulation (Connick). The DRSSTC is the newest and most efficient form of the Tesla Coil because it combines the effectiveness of the SSTC with the resonance rise of the SGTC (Dunn). This is due to the Resistor-Inductor-Capacitor circuits, or RLC resonant circuits, being energized at a specific resonant frequency (Makaa). The DRSSTC is very similar to the SSTC but has greater control over length, appearance, and sound of the spark. The DRSSTC also, however, is at increased risk of component failure and has a more complicated design, making it slightly less popular among hobbyists (Connick).

The most prominent component of a Tesla coil is the metal ball placed on top, which is known as the “top load”. The top load of a Tesla Coil acts as a capacitor in the secondary circuit, meaning that it holds a charge (Makaa). In practice, the toroid is found to be the preferred shape of the top load. This is due to its distribution of surface area near the center (Jadwani). As the coil operates, a charge will accumulate on the surface of the toroid and will discharge once a limit has been reached, creating the iconic electric sparks (Choudhury). Tesla Coils also rely on devices known as Interrupters and Controllers. The Interrupter consists of IGBTs (Insulated-Gate Bipolar Transistors) and is designed with Pulse Width Modulation and Breaks Per Second control (Dunn). Pulse Width Modulation is a technique used to encode a message into a pulsing signal (Connick). The number of Breaks Per Second control the amount of time that the system is active and reduces the likelihood of overheating (Dunn). The main functions of the Controller, on the other hand, are to reduce the current and provide overcurrent protection (Connick). The way this is done is by first using transformers, which drastically reduce the current and in turn sharply increase the voltage. This voltage is then run through several diodes and resistors to keep the circuit from overloading (Dunn).

Audio modulated Tesla Coils rely on Pulse Width Modulation (PWM) to produce sound. Through PWM, an audio signal can be transformed into high and low signals that vary with changes in audio voltage (Choudhury). This directly influences the current moving through the primary coil, which controls the current in the secondary coil. The secondary determines the charge buildup on the toroid and the resulting sparks, so this technique can be used to cause the discharges to reflect the sound of the original audio signal (Connick). Breaks Per Second (BPS), induction, and impedance are also important to the proper operation of audio manipulated Tesla Coils. As the frequent change in current can cause the systems in a Tesla Coil to overload, BPS are used to control the amount of time that the system is “on,” limiting the possibility of overload (Choudhury). When current flows within a circuit, it generates a magnetic field. When the current changes, as in an alternating current, the magnetic field that crosses the circuit changes (Jadwani). That leads to a force that opposes this change. This property is known as inductance (Choudhury). Inductors use this property to store energy in the form of electric fields (Jadwani). Impedance is related to inductance and is the measurement of a component’s resistance to a change in current. Both of these concepts are essential to the operation of Tesla Coils (Choudhury).

There are several factors to keep in mind when working with Tesla Coils that might lead to the less than ideal operation of the coil (Soleyman). Proper tuning of the coil is essential to achieve good power output. If the resonator is not driven at the correct frequency, an unnecessary strain may be put on the driver system (Jadwani). The simplest way to combat this problem is by using a small antenna near the resonator. This will measure the electric field and relay this information directly to the driver, which adjusts accordingly (Soleyman). The wires of the coils themselves have a resistance, which dissipates some energy as heat. The generated sparks themselves also act as resistors, dissipating energy in the forms of light, heat, and sound (Jadwani). In addition, because the Tesla Coil operates at radio frequencies, a fraction of the energy is radiated out as electromagnetic waves (Soleyman). Finally, due to the ionization of the air surrounding the coil, there is a phenomenon known as the Corona Effect. The Corona Effect is a continuous discharge from conductors kept at a high voltage and produces a violet halo around the conductor (Jadwani).

Conclusions

After researching the history, types, application, and construction of the Tesla Coil, I decided that I would construct a DRSSTC, as this perfected form of the Tesla Coil lends itself very well to audio manipulation. I originally set out to source all the components and designs myself, however, I quickly realized that this would become a much bigger project than I had anticipated. Fortunately, a company called OneTesla has kits with all necessary components and circuit boards included. This greatly reduces the timescale of the project, as I can focus on the construction of the coil and not have to wait for multiple manufacturers to ship individual components. The overall cost is also reduced, as they are able to buy their parts in bulk. I will also have the assurance that the coil will be properly tuned and operating correctly and efficiently. I have contacted the company, but due to a backorder the kits will not ship for a few weeks and I have not been able to begin work. This delay should not, however, prevent me from completing the project as planned before the project deadline.

The Tesla Coil was one of the most significant inventions of the early 1900s. It was mankind’s first step into the realm of wireless energy. And while it never realized its full potential as a household energy source, the concepts applied in this device paved the way to modern communication and energy transfer. Radio, Bluetooth, and the emerging trend of induction charging for mobile devices would not be possible without this pioneering effort. Modern Tesla Coil enthusiasts have modified and improved the device in ways that Tesla himself never dreamed, allowing it to work with high efficiency and accomplish stunning feats of electrical engineering. Its sparks ignited the imagination and continue to amaze and inspire today.

Works Cited

Choudhury, Abinash, R. Nikhil Kumar, and Hanhu Charan Behera. Design Of Tesla Coil. Gunupur: Gandhi Institute of Engineering and Technology, 7 Nov. 2014. DOC.

Connick, Robert. The Acoustics of Tesla Coils. Worcester: Worcester Polytechnic Institute, 8 Apr. 2011. PDF.

Dunn, E. K. DRSSTC. Lawrence, KS: University of Kansas Physics Dept., 8 May 2012. PDF.

Ercegovac, Milos D. Omnipresence of Tesla's Work and Ideas. Los Angeles: UCLA, Oct. 2006. PDF.

Jadwani, Vinay, Ashutosh S. Khope, Jyoti Sahu, N. Nagaraju, and Shivani Singh Chandel. A Project Report On "Tesla Coil" Raipur: Columbia Institute of Engineering & Technology, 11 May 2014. DOCX.

Makaa, Bernard Mumo. "Wireless Power Transmission Using Solid State Tesla Coils." Researchgate.net. 14 May 2015. Web. 10 Sept. 2015.

Mohammed, S. Sheik, K. Ramasamy, and T. Shanmuganantham. "Wireless Power Transmission - A Next Generation Power Transmission System." International Journal of Computer Applications IJCA 1.13 (2010): 102-05. Web. 11 Nov. 2015.

Petković, Tomislav. "The Achievement, Legacy, Intuition, and Cosmopolitanism of Nikola Tesla." Almagest 4.2 (2013): 60-85. Web. 11 Nov. 2015.

Soleyman, Sean. Solid State Tesla Coils and Their Uses. Berkeley: University of California at Berkeley, 14 Dec. 2012. PDF.

Tesla, Nikola. "The Transmission of Electrical Energy Without Wires." Electrical World and Engineer (1904). Tfcbooks.com. Twenty-First Century Books. Web. 17 Sept. 2015. <http://tfcbooks.com/tesla/1904-03-05.htm>.

Tesla, Nikola. "The Transmission of Electrical Energy Without Wires as a Means for Furthering Peace." Electrical World and Engineer (1905): 21-24. Tfcbooks.com. Twenty-First Century Books. Web. 17 Sept. 2015. <http://tfcbooks.com/tesla/1905-01-07.htm>.

"Tesla's High Potential and High Frequency Work." The Electrical Review 44.1,119 (1899): 730-33. Tesla-coil-builder.com. Web. 17 Sept. 2015. <http://www.tesla-coil-builder.com/Articles/Tesla_ElectricalReviewLondon_44_730_733.pdf>.

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