Transcript of "Nikola tesla the man and his coil by matthew gebben, 35p"
Nikola Tesla: The Man and His Coil By Matthew Gebben Throughout history there have been many people who have made their mark bycontributing to humanity’s advancement. Many of these people have been largelyforgotten, while some went on to become legends. Scientists such as Newton andEinstein, and inventors like Edison, rose to fame through their achievements. One man,whose work has faded from the minds of many today, managed to accomplish more inthe creation of the modern world than most. Nikola Tesla, an inventor and scientist bornin the Victorian age, was a star in his time. He transformed the world, giving companiesthe technology to send electricity to every corner of the world through the invention ofefficient alternating current systems. In order to understand this man and his creationsmore, a thorough investigation into his life and inventions, especially his famous coil, isneeded. Early Life Born in 1856 in Smiljam, Croatia, Nikola Tesla would grow up in a ruralenvironment. With a father in the church, a mother who worked the fields, and foursiblings, Tesla had an eventful childhood. He began to invent at an early age, creatingsuch devices as paddle-less waterwheels and motors driven by insects.1 Much like hismother, Tesla also showed signs of possessing great memory; his parents emphasizedimproving memory and performing mental calculations. Tesla was also a voraciousreader, learning many skills in the process. Tesla’s childhood was not without tragedy,however. At the age of five, Tesla’s brother, Daniel, died in an accident which remainsshrouded in mystery. This event would affect Tesla for the rest of his life, and it is
possible that several of his unusual habits may have had their roots there.2 His obsessivecompulsive behavior included such things as counting his steps, calculating the volumeof what he ate, and favoring “numbers divisible by three.”3 Tesla would also developseveral phobias, including a fear of bacteria. Reflecting on his own childhood, Teslawould later make several claims that did much to encourage a sort of cult following afterhis death. Tesla would claim to have seen visions of objects along with bright flashes oflight.4 Tesla’s claims, which also include superhuman hearing, among other things,invited people to make bizarre theories on his nature. These theories ranged from Teslabeing a psychic to him being a Venusian who came to Earth.5 These strange conjecturesshould in no way diminish Tesla’s true accomplishments, however. Tesla’s childhoodcontinued fairly normally, despite his supposed afflictions. In his late teens, Tesla began to earnestly take interest in invention. Using hisexcellent memory and visualization skills, Tesla would create and test ideas in his mindbefore actually producing anything physical. Tesla’s mathematical ability also becameevident in school. Despite several bouts of illness, Tesla worked through his educationand enrolled in the Austrian Polytechnic School. His life there was quite different fromhome.6 Tesla Emerging Genius and his Motor Tesla was a very studious person. Studying much of the day, Tesla wasdetermined to make the most of his time at the school. His second year brought hardship,however. The scholarship, which allowed him to live comfortably the year before hadbeen taken away, so Tesla had less than a year to stay. During this time, Tesla had plenty
of exposure to electrical equipment. One such experience is especially noteworthy.“When one day there arrived from Paris a direct-current apparatus called a GrammeMachine that could be used both as a motor and a dynamo, Tesla examined the machineintently, feeling a strange excitement. It had a wire-wound armature with a commutator.While operating, it sparked badly, and Tesla brashly suggested to Professor Poeschl thatthe design might be improved by dispensing with the commutator and by switching toalternating current.”7 (It should be noted that a commutator is a mechanical solution tomaking direct current motors. Basically, in order for the motor to generate continuousmotion in one direction, the current had to be “mechanically switched to run first one wayand then the other.”8) Although the professor thought such a feat impossible, Teslawould later go on to prove him wrong. Despite excelling at the school, Tesla’s financialsituation, not helped by his gambling, forced him to leave. Tesla would continuestudying on his own, with the problem of the alternating current motor staying in hismind. Tesla studied in Prague until he was twenty-four years old. During his studies, hehad to leave once when his father passed away in 1879. Then, in 1881, Tesla moved toBudapest and secured a job at the new telegraph office. It was here that he would havehis revelation. While exercising with a friend, the design for the new motor wassuddenly realized. “Tesla’s long, waving arms froze in midair as if he had been seizedwith a fit. Szigety, alarmed, tried to lead him to a bench, but Tesla would not sit until hehad found a stick. He then began to draw a diagram in the dust.”9 This would be therevolutionary motor that would change the world.
The basic idea behind a motor is to send an electrical current through some wiresto create a magnetic field. Then the magnetized part, the rotor, will move to align itself,giving the desired motion. A direct current (DC) motor must have to have something (thecommuatator) to physically change the magnetic field; otherwise, the rotor would simplyalign itself and stop moving. Alternating current (AC) presents the challenge of a currentthat is also changing back and forth in direction, making smooth, one-directional motiondifficult. By using more than one alternating current, Tesla realized he could create arotating magnetic field. This was done in an ingenious way. By using four coils in acircle (for two currents), each ninety degrees from the other, and by attaching eachdiametrically opposed pair to the same current (so that each pair operates on a differentcurrent) the rotor would continuously move about as the magnetic fields from the coilschanged.10 This design is outlined in the following figure provided by“http://www.allaboutcircuits.com/vol_2/chpt_13/7.html”.Figure 1. Tesla’s Alternating Current Motor. (Note the four coils positioned at twelve,three, six, and nine o’ clock. These create the rotating magnetic field mentioned before.)
By expanding upon this concept, Tesla would have a great many designs. Tesla’s First Professional Experiences Although Tesla had the full design in his mind, he built no working model at first.Instead, he continued to explore the concept and would think up many other usefulinventions in the following months. “He conceived of such practical alternating-currentmotors as polyphase induction, split-phase induction, and polyphase synchronous, as wellas the whole polyphase and single-phase motor system for generating, transmitting, andutilizing electrical current.”11 Nevertheless, Tesla had no means of building any of hisideas; thus, he returned his attention to his work at the telegraph office. However, Teslawas soon recommended to the Continental Edison Company in Paris. In 1882, Teslawould find himself working for this company, and he was on his way as an inventor. Tesla performed well at his new job, but frustration with his superiors caused himto resign and emigrate to the United States. At the time, America was the center of theelectric revolution; Thomas Edison was busy spreading his direct current system and lightbulbs across the nation. Tesla wasted no time in going to work for the famous inventor.Although Tesla was an excellent employee, the two men were fated to duel in one of thegreatest scientific and industrial competitions of the modern era. Once again, Teslawould resign, but this time he would push forward on his own. Tesla’s first attempt at business was a failure. The Tesla Electric Light Companywas created in the middle of a national financial crisis, so it came as no surprise whenTesla was forced to move on. Working as a laborer, Tesla still managed to conceive ofnew ideas. This inventiveness would help him greatly; soon Tesla attracted the attentionof “A.K. Brown, manager of the Western Union Telegraph Company.”12 Mr. Brown was
interested in Tesla’s dream of AC power, and he soon helped Tesla found the TeslaElectric Company in 1887. Now Tesla would be able to show the world what he couldreally do. Tesla soon set to work filing patents for his new AC system. He was verythorough about it, too. He filed patents for “the entire polyphase AC system. This was infact three complete systems for single-phase, two-phase, and three-phase alternatingcurrents. He experimented with other kinds too. And for each type he produced thenecessary dynamos, motors, transformers, and automatic controls.”13 These systems arestill in use today. The two-phase and three-phase systems simply have multipleoscillating signals at the same time, as shown in the following figures.Figure 2. The graph on the picture’s right shows a two-phase signal with a 90 degreephase difference. (http://en.wikipedia.org/wiki/Two_phase)
Figure 3. A three-phase signal with what appears to be a 120 degree phase difference.(http://en.wikipedia.org/wiki/Three_phase)Despite the innovations he had created, Tesla had yet to find a means to push AC as aviable power source. Many were against AC because they had already invested in theirown DC systems. One company did have an interest in AC, however. A Great Partnership and the Competition for a New Market George Westinghouse’s company had also entered the electric power market, andthey had decided to go with AC. Although their operations expanded quickly enough,Westinghouse needed to make his system more effective. It was at this time that Teslabegan to receive recognition. Tesla’s activity filing patents caught the attention of theAmerican Institute of Electrical Engineers, and he gave a well-received lecture to themon May 16, 1888.14 Hearing of this, Westinghouse went to pay a visit to the inventor. Tesla and Westinghouse got along with each other quite well. Tesla’s AC systemmust have seriously impressed Westinghouse; he made Tesla an excellent business deal.“…for his forty patents Tesla received about $60,000 from the Westinghouse firm, which
included $5,000 in cash and 150 shares of stock. Significantly, however, according toWestinghouse historical records, he was to earn $2.50 per horsepower of electricitysold.”15 Tesla would then go to work for Westinghouse, although he did not exactly getalong with the engineers; it took some effort to convince the engineers to use sixty cyclesper second (Hertz) as the frequency (60Hz was the frequency for which Tesla’s motorhad been designed). The other AC systems of the period were designed for 25, 30, or 50Hz. With the nation’s economic crisis over, companies were looking to expand and the“war of the currents” began in earnest. Not wanting to lose business, Edison began to launch attacks on AC. Edisonproclaimed AC to be too dangerous, and set about distributing flyers highlighting this. Inaddition, Edison collected animals from the neighborhood to electrocute with AC; ratherthan say the animals were electrocuted, he used the phrase “Westinghoused.”16 Edison’scampaign also managed to introduce the electric chair as a means of execution, using AC,of course. Westinghouse launched a counter-campaign to educate the public, but, luckilyfor them, Edison would soon have other matters to worry about. The Edison ElectricCompany and the Thomson-Houston Company, a business under the control of J.P.Morgan, merged in 1892 to form the General Electric Company. Unfortunately, Morganwas about to make an attempt to take control of Westinghouse’s company.Westinghouse’s determination to fight would have lasting consequences for Tesla. Westinghouse was in a position of weakness against Morgan’s empire of banks,railroads, and manufacturing firms. Morgan’s financial clout made the takeover seeminevitable, but Westinghouse merged his company with several others to form theWestinghouse Electric and Manufacturing Company. This was not enough, however;
some other way to stay afloat had to be devised. The deal Westinghouse made with Teslanow came back to haunt him. With the expansion of his business, Westinghouse had made an error. He nowowed massive royalties to Tesla due to their contract. Tesla could become an incrediblywealthy man, but then Westinghouse could not compete with Morgan. Westinghouse hadto find a way out of paying the royalties, so he confronted Tesla with the problem. Tesla,who wanted his system to succeed, had no problem with helping his friend. Tesla said toWestinghouse, “You will save your company so that you can develop my inventions.Here is your contract and here is my contract – I will tear both of them to pieces, and youwill no longer have any troubles from my royalties.”17 This act of generosity not onlysaved Westinghouse, but it also doomed Tesla to later having financial problems of hisown. Whether or not Tesla considered the possible outcomes of renouncing his royaltiesis unknown, as he was busy performing new experiments. New Horizons In his lectures, Tesla would demonstrate the products of his new research. Heoften displayed his new lamps, many of which were glass containers filled with gas.These were “the forerunners of today’s fluorescent lights.”18 Tesla had also begun todiscuss the possibility of sending power through the air or drawing it out of nowhere.These ideas would prove to be some of the inventor’s more controversial thoughts.However, Tesla also introduced his carbon-button lamp during these demonstrations. The carbon-button lamp was a relatively simple device. It consisted of a partiallyevacuated glass bulb with a small ball of “refractory material” in the center. The ball, orbutton, was suspended there with the wire which would supply electricity. The whole
lamp, once sealed, would be supplied with high frequency electricity. The molecules ofgas left in the bulb would fly away from the button, but would be repelled back by theglass walls. These molecules would bombard the button, heating it, and the processwould repeat. The bulb is said to have burned very brightly, and the button would oftenget so hot that it would be destroyed. Tesla tested different materials for use as thebutton, and carborundum (aluminum oxide) lasted the longest. Tesla stated in an addressto the American Institute of Electrical Engineers that this lamp was very efficient.19Tesla had indeed begun work on many projects other than motors. Tesla built many other notable inventions during this time. One of these, perhapshis most famous, was the Tesla coil. This device is simply “an air-core transformer withprimary and secondary coils tuned to resonate – a step-up transformer which convertsrelatively low-voltage high current to high-voltage low current at high frequencies.”20Because this is such a famous invention, a full discussion of its details will be left untilTesla’s life has been adequately covered. Although Tesla worked on many subjectsduring the 1880s, the 1890s would prove to be just as productive, if not more so. The 1890s began with Tesla putting everything aside and returning to Croatia.His mother was dying, and Tesla was greatly affected. After her death, Tesla was sickfor quite some time. Nevertheless, Tesla resumed his scientific explorations uponrecovering. Tesla, who had taken an interest in using electromagnetic waves, gave aseries of demonstrations in 1893 not only detailing but also testing radiocommunication.21 Tesla was making ground-breaking contributions to radio years beforethe traditionally accepted inventor of radio, Marchese Guglielmo Marconi, demonstratedhis system. As later court cases would show, the title of inventor of radio would be hotly
contested for years to come. However, as these problems had not yet presentedthemselves, Tesla had to turn his attention to other concerns. Success and Disaster A major success came for Westinghouse and Tesla at the 1893 Chicago World’sFair. The whole fair was supplied with power using Tesla’s AC system, and became awindfall for Tesla and Westinghouse. Westinghouse was able to gain people’sconfidence by lighting up the fair and showing the safety of AC. Tesla was able to seehis system make an excellent impression on the visitors and had a chance to display hisother inventions. The fair was incredibly successful, and it heralded a new age oftechnological progress. By this time, Tesla had become very famous, and the inventorwould soon enjoy the fruits of his success. At the time, the Waldorf-Astoria Hotel was where all of the movers and shakerswould gather to socialize after work. Tesla, who enjoyed having as high class a life aspossible, often went there to mingle with the rich and famous. The great opportunitythese gatherings afforded was the chance to find financiers. Tesla was also able toincrease his fame through his encounters with others, especially the press. Tesla seemedto have affected many people, as there are quite a few letters people wrote admiringlydescribing the inventor. Despite keeping up a good social image, Tesla devoted himselfmore to his work than to other people. Tesla had been making progress with his radio experimentation, but this was to besoon eclipsed. In late 1893, Tesla was informed by Westinghouse that the power ofNiagara Falls was to be harnessed to supply electricity, and it would use Tesla’salternating current system. Although Westinghouse was not totally in charge of the
project – General Motors would construct the power lines – Tesla’s AC system wasagreed upon by all involved.22 The Niagara project proved to be very successful, andthere is a large statue of Tesla at Niagara Falls to this very day. With the Niagara projectgoing smoothly, Tesla returned to his New York laboratory. Hoping to make further progress towards his goal of wirelessly transmittingenergy, Tesla began to use higher and higher voltages. Using a modified coil he hadbuilt, Tesla was able to get roughly one million volts.23 Occupied with testing newinventions and contemplating his various theories, Tesla could not have been morecontent. However, this happiness was not to last. In early 1895, Tesla’s laboratoryburned to the ground, destroying everything he had been working on. The fire’s sourcewas never really identified, but it was theorized that Tesla’s investigation into theproduction of liquid oxygen may have been a factor.24 Now Tesla had to start over again. A Fresh Start Tesla’s fame helped him a great deal now; capital came in quickly, and theinventor quickly set to work preparing a new laboratory. With the discovery of X-raysannounced, Tesla began his own investigation. At the time, the danger posed byoverexposure to the rays was unknown, and Tesla learned first-hand that safety measureshad to be taken. Both Tesla and an assistant were injured, although the assistant sufferedthe most; he was standing very close to the emitting source for five minutes.25 Thisaccident was just one of many that Tesla would be lucky to survive. For instance, in1896 Tesla received a shock of roughly 3.5 million volts at a low current.26 Tesla’s driveto achieve higher and higher potentials would mean this would not be an isolatedincident.
Continuing his research, Tesla pushed his radio technology to new heights. Soonhe was able to transmit and receive over reasonably distances of a few miles. In 1898,Tesla both received a patent for and tested a remote control boat.27 Not content with thecurrent technology, Tesla once again pursued the wireless transmission of power. Hisannouncements to the press would seem terribly premature today; Tesla’s statementsoften made it sound like a great discovery had been made, when, in fact, nothing concretehad been produced. This showmanship by Tesla not only increased his fame and helpedto acquire financial support, but would also later on work against him. One excellent example of this exaggeration was the infamous earthquakemachine. Tesla had long theorized that if one sent a wave through some substance (byhitting it, for example), energy could be slowly added by tapping it exactly when thewave came back to the point of origin. This theory was blown out of proportion by Teslahimself when he claimed to have used one of his mechanical oscillators to cause anearthquake. Supposedly, he attached the oscillator to a pillar in his laboratory and thevibrations went into the bedrock. According to Tesla, the vibrations were amplified eachtime the wave returned to the oscillator, and eventually a small earthquake occurred.There is no proof that this ever happen, but the myth persisted (no doubt Tesla helped: heclaimed the same principle could be used to shatter the Earth itself).28 This story was putto the test on a Discovery Channel show called Mythbusters.29 In this program,oscillators which performed the same function as Tesla’s design were used to try and geta bar of steel to sway violently. The mechanical oscillators seemed to be too imprecise,but an electromagnetic linear motor (it has a bar that moves straight back and forth) got areaction. Able to tune the frequency with precision in the hundredths of a hertz, the bar
of steel did indeed begin to vibrate violently at a certain frequency. When attached to aunused bridge, not much happened until another specific frequency was reached. Thenvibrations could be felt throughout the structure, but nothing like Tesla claimed. Even ifTesla was exaggerating, the theory manages to hold some weight. In betweenincreasingly incredible announcements, Tesla was still busy putting out noteworthy work. Around the turn of the century, Tesla was still busy with his remote controlvehicles. Nevertheless, progress in other fields was made. Fascinating examples of thiscan be found in patents 723,188 and 725,605. The patents actually were useful long afterTesla’s death. “Their [Brattain, Bardeen, and Shockley] patents and the Tesla patentswere both directed at applications in the communications field, he [Leland Anderson]notes. Both patents are combined to produced the physical embodiment of a solid-stateAND gate.”30 The AND gate is just one of the logic gates so important to the operationof computers today. Even with successes such as these, Tesla’s desire to pursue radioand the wireless transmission of electricity drove him to seek new grounds in which towork. Colorado Springs In 1899, seeking higher voltages and more space, Tesla arrived in ColoradoSprings. Working outside of town, Tesla constructed a special laboratory where he couldcarry out experiments at very high voltages. Luckily for Tesla, power would be free:Leonard Curtis, the man who suggested Colorado Springs to the inventor, had invested inthe local power plant.31 The new lab had an antenna-like mast coming out the top, with ametal ball topping it (something like the top of a giant Tesla coil). This building wouldhouse the magnifying transmitter.
The magnifying transmitter seems to have been a large, modified Tesla coil.What was special about this was the secondary coil. Tesla told Electrical Experimenterthat the secondary coil’s area was very large and its parts were “arranged in space alongideal enveloping surfaces of very large radii of curvature, and at proper distances fromone another thereby insuring a small electric surface density everywhere so that no leakcan occur even if the conductors are bare.”32 In other words, Tesla avoided dischargesfrom the surface by increasing the area and thus decreasing the surface density ofelectricity. Tesla said in the same article that either high voltage or current were possible,but not both. He also stated that any frequency would work, and that the “tension,” orvoltage, only depended on “the curvature of the surfaces on which the charged elementsare situated are the area of the latter.”33 The whole system was designed to effectivelyinteract with the “globe” (Whether this refers to the Earth or the ball on the antenna isdifficult to determine considering the context). With this massive device, Tesla hoped topush the envelope of projecting electrical power. The magnifying transmitter appears to have been quite powerful. It seems that thedevice created thunder from its long sparks and imparted an electrical charge to theground that could be felt easily. Expanding the facility’s capabilities, Tesla prepared tomake a high voltage, high current test. The test was impressive: very long sparks jumpedfrom the antenna’s top, and the thunder could be heard fifteen miles away.34 However,the test was abruptly cut short by a power failure; the local power plant’s generator hadfailed catastrophically. After helping to restore the generator, Tesla continued hisexperiments in Colorado Springs. Indeed, his endeavors attracted a great deal ofattention, much to his annoyance.
Tesla, in order to be more secretive, had boarded up the window. This, inaddition to Tesla’s ill-advised decision to use a spring to make the main switch easier toclose, would lead to another of Tesla’s close calls. While working alone with a verylarge coil, the spring mechanism failed, closing the circuit. Tesla was forced to dive tothe floor and crawl to the switch as electrical streamers filled the room. By the time heopened the switch the building was burning. He was lucky to have been able toextinguish the blaze. Even with events such as this, Tesla had reached new heights.35 In Colorado Springs, Tesla’s records show that 12 million volts and 1100 ampereshad been the highest voltage and current he reached. It also appears that ball lightningmay have been formed by some of the coils, and the radio receiver he built was quitepowerful for the time. However, Tesla’s dream of transmitting electrical power never gottoo far. Although he believed he had made great progress, the idea would not get muchfurther. In 1900, Tesla moved to New York, and began work on what would result in hisgreatest financial mistake.36 The Beginning of the End Hoping to create a worldwide radio system, Tesla set about looking for capital.He was not having much success until J. Pierpont Morgan agreed to fund the project. Inorder to build a broadcasting station on the East Coast, Tesla bought an area of land onLong Island. There he built a famous tower which became the symbol of the place Teslacalled Wardenclyffe. This 187 foot tower would act as a massive antenna. However, asthe equipment started to come in, Marconi, using one of Tesla’s patents and a station onCape Cod, sent a signal across the Atlantic Ocean; it appeared that Marconi was going toprofit by using technology he had no permission to use. Marconi’s growing fame made
Wardenclyffe’s increasing cost even more frustrating. Quickly running out of money,Tesla again petitioned Morgan but found the financier uninterested. Despite Tesla’stechnical successes, Morgan lost interest and the money began to run out. By 1906,Wardenclyffe’s fate was assured, and work soon stopped. The site fell into disrepair andwas finally sold in 1915.37 Tesla’s fortunes would never be the same again. Tesla’s misfortune seemed to be growing rapidly. His fame made him manyenemies within the scientific community, and financiers were noticing a history ofunprofitable projects and wild claims. Along with this, the credit for who invented radioincreasingly appeared in jeopardy. Marconi, with his financial success, managed to get apatent on his wireless system. For decades, Marconi maintained his position as theinventor of radio, but not without controversy. Many lawsuits contested this claim,including one by Tesla in 1915. Tesla’s enemies were quick to defend Marconi, but thecredit would not stay with them forever. In 1943, only months after Tesla’s death,Marconi’s patent was revoked by the US Supreme Court. Although Tesla would finallyget the credit he deserved, he would not live to see it.38 Tesla would simply have topersevere with what he could get. Tesla had been affected by the misfortunes that plagued him. Some of Tesla’smore unusual and unflattering traits became more prominent. His habit of showing off tothe press became more irresponsible. “Tesla would advance scientific claims recklessly,discussing them with reporters fresh from the moment of inspiration with subjecting hisideas either to experimental verification or even much reflection.”39 Needless to say, hiscredibility suffered as a result. Tesla’s self-promoting may have been an attempt toattract the attention of financiers, but its success is debatable. Tesla also picked up the
unusual habit of taking care of hurt pigeons, a habit that would be with him for the rest ofhis life. Following attacks on his reputation or his inventions, Tesla also became moreaggressive in defending himself. Tesla’s creative genius had not dried up, however. Fleeting Optimism By 1906, Tesla had a new invention with which he hoped to achieve financialsuccess. This was the bladeless turbine, and, over the next few years, Tesla woulddevelop it into an effective machine. The idea was fairly simple: send a high pressure gasbetween a set of disks. The material moving through would sort of stick to the surface ofthe disk to get it to move. Ordinarily this would be an ineffective way to drive anything,as most of the material would be too far from the surface, taking the path of leastresistance. Tesla realized that by spacing the disks closer together efficiency could beincreased.40 This turbine had the great advantage of simplicity. Thus Tesla set aboutpromoting the new invention and began to court possible investors and buyers. During the first few years of the 1910s, Tesla had some successes with histurbine. He had been able to interest several different European nations in licensing themachine, including Belgium, from which Tesla received $10,000.41 Despite a fewsuccesses, Tesla remained far short of the funds he needed and began to petition J.P.Morgan, who had inherited his late father’s (J. Pierpont Morgan) business. This provedto be not only unsuccessful, but harmful, as Morgan took the opportunity to bill Tesla forthe previous loan’s interest. Tesla continued to have bad luck, but in 1915 somethinghappened to offer hope for the future. In 1915, the New York Times reported that the Nobel Prize in physics would beshared by Tesla and Edison. Although surprised, Tesla speculated to reporters about
what discovery of his might have led to this honor. Soon, the news had spread across theUnited States, and things were looking up for Tesla. However, the whole situation wasan illusion. The newspapers had been premature in their announcement of the winners,and the prize would, in fact, not go to either Tesla or Edison. The recipients would beWilliam Henry Bragg and his son for discovering the structure of crystals.42 Thecircumstances behind the rumor were never fully known, but the whole event must haveseemed cruel to Tesla. His predicament continued to worsen. Tesla’s Final Years Tesla’s turbine would also prove to be largely unsuccessful. The first period ofinterest in the machine was ephemeral. Many were unwilling to invest in a new turbinewhen the current ones worked fine, and Tesla’s turbine was, like most machines, havingproblems. Tesla used German silver for the disks, but the operation speeds would proveto be too much for this material. Indeed, suitable material for the disks would not beavailable for years to come. Without enough money to do much of anything, Teslaturned to the things he could do: thinking and speculation. Although Tesla was still filing patents on occasion, the majority of work forwhich he would be known was already in the past. His time was now spentcontemplating powered flight and designing lightning rods, among other things. Tesla’sfame had, in one way, worked against him. Many thought the inventor was very wealthy,so it came as a shock to many when Tesla’s relative poverty came to light in 1916. InMarch of that year, Tesla was brought to court because he had not paid some of his taxes.During this trial, Tesla’s real financial situation was totally revealed. While Tesla musthave been embarrassed by the whole situation, there was one positive outcome.
With the news of Tesla’s debts now common knowledge, many electricalengineers felt that a great injustice had been done. Tesla had practically ushered in themodern electrical age, and yet he was unrecognized for his achievements. With this inmind, the American Institute of Electrical Engineers decided to give Tesla the EdisonMedal, their highest award. Initially, Tesla vehemently denied wanting anything to dowith the award that bore the name of one of his greatest rivals. One of the engineers whopushed for Tesla to receive the prize, B. A. Behrend, set about trying to persuade the manto accept the award. Although it took many visits, Tesla eventually agreed. Despite allhis earlier protests, Tesla attended the ceremony and gave a fairly long speech. Teslawould treasure the Edison Medal for the rest of his life. After receiving the Edison Medal, Tesla was a little more optimistic. He beganworking to get out of debt and was trying hard to make successful business ventures. Itwas an honest series of attempts, but nothing substantial came of it. Instead, Tesla wasfinding himself more and more out of place with the world. Tesla, with his outdatedscientific beliefs in things such as the ether, could not come to agree with the work beingdone in quantum mechanics and relativity. As science and technology advanced further,Tesla’s work appeared to be slipping out of memory. Even the Westinghouse Company,so much in debt to Tesla for his contributions, appeared not to remember or care: theyhad turned down Tesla’s radio system while setting up their own.43 With the end of hiscareer seeming to be at hand, and with little recognition, it is no wonder that Teslabecame more eccentric. As he aged, the pigeons which Tesla cared for became ever more important tohim. Kenneth M. Swezey, a friend Tesla had made in the 1920s, wrote that the elderly
scientist had dozens of pigeons in his care. Tesla could not even keep all of them in hishotel room. Among all the birds, there was a white one to which Tesla had a deepemotional attachment. When this pigeon died, Tesla was devastated. Tesla claimed hecould communicate with this bird, and that they had some sort of connection. Hesupposedly said to his future biographer, “Yes, I loved that pigeon, I loved her as a manloves a woman, and she loved me. When she was ill I knew, and understood; she came tomy room and I stayed beside her for days.”44 While this behavior in Tesla was certainlyunusual, it did show Tesla emotional depth. Even with the end of his life not far off,Tesla proved to still have a knack for publicity. The last decade of Tesla’s life was spent making flamboyant claims. Althoughnot everything he said was outlandish, many were quite unrealistic. Taking advantage ofhis birthday parties to talk to the press, Tesla would announce things such as havingdiscovered a totally new, unlimited and free source of power. Of course, only vaguedetails were given, and nothing ever came of the matter. Indeed, much of what Teslaclaimed during this period would only fuel the theories of occultists later on, furtherobscuring Tesla’s real achievements. An excellent example of this is Tesla’s so-calleddeath ray. The New York Times reported on the device on July 11, 1934 with the claimthat it was “powerful enough to destroy 10,000 planes 250 miles away.”45 Althoughsome rudimentary designs were drawn up, there is no evidence a real working device wasever built. Nevertheless, after Tesla’s death, something of a conspiracy theory emerged.It was claimed that the government had taken Tesla’s technical designs, and the conceptshad been taken up by both the US and the Soviet Union. Supposedly, Tesla’s death beam
theories influenced their work on directed energy weapons. Such stories are fantastic, butthey have made it sometimes difficult to distinguish myth from reality in Tesla’s life. In the late 1930s, Tesla’s health began to falter. The elderly inventor was struckby a taxi in 1937 and refused to go to a doctor. He eventually caught pneumonia and wassick until the spring. Tesla never fully recovered, and his health wavered until 1943. Onthe fourth of January of that year, Tesla was going to help an old working partner set upan experiment, but had to leave early due to chest pains. Returning to his hotel room,Tesla confined himself alone for several days. On the eighth, when a maid checked theroom, the inventor was found dead. Tesla had died the day before, probably of acoronary thrombosis.46 The long and fascinating life of one of the modern world’sgreatest inventors had come to an end. Nikola Tesla’s eighty-six years of life had transformed the world. Besides his ACmotors, Tesla had created a myriad of inventions. Tesla’s AC system made electricalpower practical and eventually brought electricity to every corner of the world. Tesla’sfundamental radio patents paved the way for the mass media so ubiquitous today. Yet,many of these great contributions are largely unrecognized today. However, one ofTesla’s inventions had enjoyed popular recognition for various reasons. This invention isthe Tesla coil. The Tesla Coil The Tesla coil has been around for more than a century now, and its uses havechanged with time. What was once used for radio equipment and some medicalequipment (of an often unrealistic nature) is now used to generate lightning effects forentertainment. To put it simply, a Tesla coil is a special transformer capable of putting
out a high-voltage, high-frequency signal. Tesla designed the device to do so by aningeniously simple method. How it Works The Tesla coil is not just one coil, but rather a set of four assembled into twotransformers. One of these transformers is simply a step-up transformer used to give ahigh voltage from a relatively low-voltage source. This transformer, which operates at 60Hz from the power line, often has an iron core to increase coupling. The secondtransformer is a step-up, air-core transformer. This transformer has an air-core because itneeds to operate at radio frequencies, and the iron core of most transformers is a poorchoice for this. The common iron core is used to increase inductance, but at frequenciesabove 1 kHz the electron spins in the iron cannot keep up with the applied magnetic field,resulting in huge power losses.47 The air-core transformer does not suffer from themassive power losses an iron core transformer would have at radio frequencies. Betweenthe two transformers, however, lie the “guts” of the Tesla coil, and the mechanism forshifting to high frequencies. A spark gap, a capacitor, and an inductor are wired up between the twotransformers. The set-up of this primary circuit can be found in the following figure,courtesy of “http://www.richieburnett.co.uk/parts.html”.
Figure 4. The basic configuration of a Tesla coil. This set-up means that the primary circuit, that being the spark gap, the capacitor,and the inductor (primary coil), function as a separate circuit when the oscillations withthe secondary begin. Once the air in the spark gap ionizes and breaks down, the capacitordischarges most of its charge into the newly created loop. Then the inductor resists thecurrent, eventually sending the current back to the capacitor. The cycle then repeats; allthis happens very quickly. In fact, the current, under perfect conditions, oscillates at theresonant frequency, given by the following equation: 1fo = 2π LCEq. 1.48 Indeed, this equation governs the resonant frequency of both the primary andsecondary circuits. To help with this explanation of a Tesla coil, an example wasdesigned and constructed over a period of time. The procedure of its design, along withits issues, will help create a better understanding of the functioning.
The Design To begin, a resonant frequency was chosen. In this case, 700 kHz was selectedbecause a high frequency was wanted. From there, the wavelength (in feet) wascalculated using the classic equation λ=c/f (Eq. 2). Note that English units are often usedbecause many of the equations concerning Tesla coils are in those units (and areapproximations). Plugging in 9.84*108 ft/sec for c, and using the chosen frequency for f,a wavelength λ is equal to 1405.7 ft. Since it is easier to begin on the secondary coil, thisis where the design begins to take shape. The secondary coil acts like a vertical antenna,so rules applicable to antennas must be used. In this case, since the system is classed as amedium-frequency antenna, a quarter wavelength antenna length is preferable; thesecondary resonates the best with a length of λ/4.49 Dividing the calculated wavelengthby four gives 351.4 ft, the length of wire needed for the secondary. A fine wire(26AWG) was chosen for this to give a high number of turns. With its insulation, thewire has a diameter of 0.032 inches. Then, a PVC pipe with an outer diameter of 2.355inches was chosen as the base for the coil. Using these pieces of information, and theformula Dπ+d (D is the pipe diameter, d is the wire diameter)50, the length of wire perturn can be calculated (it is 7.4 inches). Dividing the length of wire by the length per turngives the number of turns, which happens to be 568.7 (which, multiplied by the diameterof the wire gives the coil height, 18.2 inches). Of course, these numbers are justapproximations when the coil has been constructed, due to the somewhat crude methodsused. From here, equation 1 is the determining factor. Since the secondary coil has an inductance and a capacitance of its own (plus thecapacitance of the toroid), the circuit on the secondary is nearly identical to the primary’s
circuit. There are also several approximate equations for determining these values. Theyare as follows: A2 N 2 Ls = 9 A + 10 HEq. 3. The Wheeler Formula. (The equation is accurate within 1% if the coil height H isgreater than the pipe radius A. N is the number of turns, and all length units are ininches, while the value of the inductance, Ls, is in microhenries.51) 1Cs = 4π ( fo 2 Ls ) 2Eq. 4. The capacitance for a helical coil. (The capacitance Cs is in farads, the resonantfrequency fo is in hertz, and the inductance Ls is in henries.52) CSCT = 1.4(1.2781 − ) * πCS (OD − CS ) ODEq. 5. The capacitance for a toroid. (The capacitance CT is in picofarads, CS is thecross-sectional diameter in inches, and OD is the total outside diameter in inches.53) In the case of the test coil, the toroid has an outside diameter of 11.1 inches and across-sectional diameter of 3 inches. This results in a toroid capacitance of about1.24*10-11 farads. When the known dimensions of the coil are put into the Wheelerformula, the coil inductance is found to be nearly 0.00233 henries. Using this, the coilcapacitance turns out to be 2.22*10-11 farads. Note that these numbers suggest that theactual resonant frequency of the coil will not be 700 kHz. Instead, using equation 1 andadding the coil and toroid capacitances, the operating resonant frequency ends up being561090 Hz. This is not a problem, provided that the primary circuit is designed with thisin mind. The operating resonant frequency is used with a modified version of equation 4 tofind the dimensions of the primary coil. For the sake of convenience, a high-voltagecapacitor capable of handling radio-frequency circuits that was on hand was used. Thishad a capacitance of roughly 0.005 μF and a maximum voltage of 15,000 VRMF. Putting
this into equation 4 with the capacitance and inductance switched, the needed inductanceis found to be about 16.1 μH. Then equation 3 can be used since both the wire and thecoil form had already been selected. Choosing a height of about 25 inches (to completelyencase the secondary), equation 3 yields a turn number of almost 37.4 turns. The chosenwire was 18 AWG with heavy insulation, giving a total diameter of 0.016 inches. A 3.5inch diameter PVC pipe was used as the primary coil form, so as to let the secondary sitinside the primary. This arrangement would presumably provide the best arrangement, asthe setup allows for the greater interaction of the magnetic fields. The solenoid shapecreates a magnetic field that goes up in the center of the coil, following the overalldirection of the current.54 This way, the secondary is surrounded by the primary’s field,and a current forms to oppose it according to Lenz’s law.55 Of course, since thefrequency will be high, the magnetic field is constantly switch direction, resulting in thesecondary coil’s alternating current. Checking the operating frequency, the primaryshares the secondary coil’s resonant frequency. The total primary coil wire length endsup being 34.3 feet. The design is now done, but there are still several more details tocover. One convenient item to note is that the impedance for both the primary and thesecondary is the same. Both take the following form: jZ = RT + jωL − ωCEq. 6. General form of coil impedance. 1 2| Z |= RT 2 + (ωL − ) ωCEq. 7. The general magnitude of coil impedance.56
Only the dimensions of the values differ between coil sides. On the secondarycoil, the resistance is supplied by the coil’s wire and by the separation of the terminalfrom a ground; the inductance and capacitance are supplied by the coil and its terminal.The primary side is more complex. Although the inductance simply comes from the coil,and the capacitor gives the circuit most of the capacitance, the resistive impedance comesfrom several sources. One of these is just the wire’s own resistance. The other twosources are slightly more complicated. The spark gap does offer some resistance thatcannot be totally ignored. However, this resistance is not too great once the air betweenthe terminals has ionized. The most interesting cause of impedance in the primary circuitcomes from the secondary coil. As previously stated, the primary coil’s magnetic field causes an opposing currentto form in the secondary coil. As might be expected, the secondary coil’s current thencreates its own magnetic field in the opposite direction. The result is a sort of reflectedimpedance in the primary. This adds an extra term to equation 7 for the primary circuit.Although the new term may appear simple, the truth is that there is some complexity.The term takes this form: (ωpM ) 2Z Re f = ZsEq. 8. The reflected impedance.57 (Notice here that the operating resonant frequency isspecifically for the primary, while the impedance in the denominator is for the secondarycoil.) The fact that the coefficient of mutual inductance is here signifies that thegeometry of the coils in relation to one another greatly affects the reflected impedance. Alarge mutual inductance results in a large impedance. As with many aspects of building aTesla coil, the equations for this mutual inductance are mostly empirical and are fairly
messy.58 This also holds true for the impedance of the secondary coil, as the calculationof the resistance of the coil is made difficult by certain phenomenon at radio-frequencies,such as the skin effect (which refers to the current being localized to the outer areas of thewire due to “eddy currents”59). However, the reflected impedance would only reduce thecurrent and performance, rather than affect the functionality. The actual coil should benoted before continuing, however. Testing With the design done, the actual setup should be detailed some more. Althoughthe following photographs are fuzzy, the design can be seen with some minorexplanation.
Figure 5. The Setup. (The tall gray tower on the left is the primary coil encasing thesecondary coil. The long wires on both of its sides are connected to the ground, allowingfor easy discharges.)Figure 6. The Primary Components. (The black box on the top is the high-voltagetransformer, and the red wire coming from its left terminal is connected to the gray-colored choke. From the choke, the wire goes to several resistors in series. Note thatonly one resistor is above the circuit board, and two are attached below. Then the wiregoes to the large cylindrical capacitor and its path splits; in addition to going to thecapacitor, the wire also goes to the spark gap in the upper right of the picture. Wiresfrom the other terminal of the capacitor and spark gap are attached to the primary coil.Finally, the spark gap is also connected to the HV transformer.)
Figure 7. The Coil Tower and Toroid. This setup, crude as it may be, was constructed according to the calculateddesigns. Once construction was complete, testing began. When the system wasconnected to the power outlet several loud sparks were created. The spark gap ended upcreating the brightest and loudest spark. The sparks from the toroid were not soimpressive, but managed to cross roughly 7cm of air to get to the grounded copper wiresnevertheless. When the toroid was traded for a copper spike a small, continuousdischarge formed at the end, creating a small corona. It should be noted, however, thatremoving the toroid should further reduce performance, and this did indeed seem tooccur. The machine worked great for a while, and was only used for a short period eachtime. After several runs, however, a setback presented itself.
Error and Correction After roughly 10 minutes of operation, a serious problem arose. When turned on,the coil would not spark. The spark gap did not fire, either. This seems to have resultedfrom the fact that the primary circuit is not totally disconnected from the power source.Without proper measures being taken, some of the primary circuit’s radio-frequencycurrent leaks back into the high-voltage transformer. Since the transformer is designedfor lower currents and lower frequencies, the result is fairly detrimental. The iron core ofthe transformer causes large power losses, and the energy goes into heat. In the case ofthe test Tesla coil, the 12,000V transformer was broken by this RF current. In order toprotect against this, a choke, an iron-core inductor, was put between the primary and thetransformer. This way, any RF current would be countered before reaching thetransformer. In addition to this, the current in the system was reduced by adding powerresistors. This, combined with the use of a 10,000V transformer, resulted in somewhatpoorer performance, giving weaker streamers about 4cm long. The end result was thatthe coil diagram changed a bit.Fig. 8. The practical setup of a Tesla coil. (The power resistors and choke have beenadded next to the high-voltage transformer, while the primary coil’s impedance, naturaland reflected, has been represented by an additional resistor in the primary circuit.)
However, aside from its rather lackluster output, the Tesla coil was designed andconstructed successfully. The sparks produced seemed to be quite powerful, and werecapable of penetrating roughly a centimeter of wood to reach the ground. It seems to be avery effective means of attaining high voltages and frequencies. The Tesla coil is a fairly complex system, and there are still many details thatcould be covered. It seems as though much of the material on the subject is, however,empirical in nature. The most useful equations are approximations, but, like many high-voltage devices, the tolerances are high. The Tesla coil is an ingenious means ofgenerating high-voltage, high-frequency electricity. Its design serves as an example ofNikola Tesla’s genius. Bibliography 1. “Tesla: Man Out of Time.” Margaret Cheney. Simon & Schuster, New York City, 2001. Pages 26-27. 2. Abid, page 29. 3. Abid, pages 19 & 29. 4. “My Inventions.” Nikola Tesla. Electrical Experimenter, May, June, July, October 1919, republished by Skolska Knjiga, Zagreb, Yugoslavia, 1977, pages 12-13. 5. “Tesla: Man Out of Time.” Margaret Cheney. Simon & Schuster, New York City, 2001. Page 112. 6. Abid, pages 32-39. 7. Abid, page 40. 8. “Tesla: Master of Lightning.” Margaret Cheney & Robert Uth. Barnes and Noble Publishing, Inc., New York, 1999. Page 21. 9. “Tesla: Man Out of Time.” Margaret Cheney. Simon & Schuster, New York City, 2001. Page 44. 10. “Tesla: Master of Lightning.” Margaret Cheney & Robert Uth. Barnes and Noble Publishing, Inc., New York, 1999. Page 21; “The Inventions, Researches and Writings of Nikola Tesla.” Thomas Commerford Martin. Barnes and Noble, Inc., New York, 1995. Pages 9-15. 11. “Tesla: Man Out of Time.” Margaret Cheney. Simon & Schuster, New York City, 2001. Page 45. 12. Abid, page 60. 13. Abid, page 61.
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