Editing Wireless power transfer (section)

== History ==

=== 19th century developments and dead ends ===

The 19th century saw many developments of theories, and counter-theories on how electrical energy might be transmitted. In 1826, [[André-Marie Ampère]] discovered a connection between current and magnets.  [[Michael Faraday]] described in 1831 with his [[Faraday's law of induction|law of induction]] the [[electromotive force]] driving a current in a conductor loop by a time-varying magnetic flux. Transmission of electrical energy without wires was observed by many inventors and experimenters,<ref>[[Luigi Galvani]] (1791), Peter Samuel Munk (1835), [[Joseph Henry]] (1842), Samuel Alfred Varley (1852), [[Edwin Houston]], [[Elihu Thomson]], [[Thomas Edison]] (1875) and [[David Edward Hughes]] (1878)</ref><ref>{{cite book |first1=T. K. |last1=Sarkar |first2=Robert |last2=Mailloux |first3=Arthur A. |last3=Oliner |first4=M. |last4=Salazar-Palma |author4-link=Magdalena Salazar Palma|first5=Dipak L. |last5=Sengupta |title=History of Wireless |publisher=John Wiley & Sons |year=2006 |pages=258–261 |isbn=9780471718147 |author-link1=Tapan Sarkar |author-link3=Arthur A. Oliner}}</ref><ref>Christopher H. Sterling, Encyclopedia of Radio 3-Volume, Routledge – 2004, page 831</ref> but lack of a coherent theory attributed these phenomena vaguely to [[electromagnetic induction]].<ref>{{cite book |first=W. Bernard |last=Carlson |title=Innovation as a Social Process: Elihu Thomson and the Rise of General Electric |publisher=Cambridge University Press |year=2003 |pages=57–58}}</ref> A concise explanation of these phenomena would come from the 1860s [[Maxwell's equations]]<ref name="Shinohara">{{cite book |url=https://books.google.com/books?id=TwegAgAAQBAJ&pg=PP11 |last=Shinohara |year=2014 |title=Wireless Power Transfer via Radiowaves |page=11 |publisher=John Wiley & Sons |isbn=9781118862964}}</ref> by [[James Clerk Maxwell]], establishing a theory that unified electricity and magnetism to [[electromagnetism]], predicting the existence of electromagnetic waves as the "wireless" carrier of electromagnetic energy. Around 1884 [[John Henry Poynting]] defined the [[Poynting vector]] and gave [[Poynting's theorem]], which describe the flow of power across an area within [[electromagnetic radiation]] and allow for a correct analysis of wireless power transfer systems.<ref name="Shinohara" /><ref name="Angelo">{{cite book |last1=Angelo |first1=Joseph A. |title=Encyclopedia of Space and Astronomy |publisher=Infobase Publishing |date=2009 |pages=292–293 |url=https://books.google.com/books?id=VUWno1sOwnUC&pg=PA293 |isbn=978-1438110189}}</ref> This was followed on by [[Heinrich Rudolf Hertz]]' 1888 validation of the theory, which included the evidence for [[radio wave]]s.<ref name="Angelo" />

During the same period two schemes of wireless signaling were put forward by [[William Henry Ward]] (1871) and [[Mahlon Loomis]] (1872) that were based on the erroneous belief that there was an electrified atmospheric stratum accessible at low altitude.<ref>{{cite book |first=Christopher |last=Cooper |title=The Truth About Tesla: The Myth of the Lone Genius in the History of Innovation |publisher=Race Point Publishing |year=2015 |pages=154, 165}}</ref><ref>{{cite book |first1=Theodore S. |last1=Rappaport |first2=Brian D. |last2=Woerner |first3=Jeffrey H. |last3=Reed |title=Wireless Personal Communications: Trends and Challenges |publisher=Springer Science & Business Media |year=2012 |pages=211–215}}</ref> Both inventors' patents noted this layer connected with a return path using "Earth currents"' would allow for wireless telegraphy as well as supply power for the telegraph, doing away with artificial batteries, and could also be used for lighting, heat, and motive power.<ref>{{cite book |first=Christopher |last=Cooper |title=The Truth About Tesla: The Myth of the Lone Genius in the History of Innovation |publisher=Race Point Publishing |year=2015 |pages=154}}</ref><ref>{{Cite web |url=https://earlyradiohistory.us/sec021.htm |title=21. Fakes, Frauds, and Cranks (1866–1922) |website=earlyradiohistory.us}}</ref> A more practical demonstration of wireless transmission via conduction came in [[Amos Dolbear]]'s 1879 magneto electric telephone that used ground conduction to transmit over a distance of a quarter of a mile.<ref name="Christopher Cooper 2015, page 165">{{cite book |first=Christopher |last=Cooper |title=The Truth About Tesla: The Myth of the Lone Genius in the History of Innovation |publisher=Race Point Publishing |year=2015 |pages=165}}</ref>

=== Nikola Tesla ===
[[File:TeslaWirelessPower1891.png|thumb|upright=1.5|Tesla demonstrating wireless transmission by "electrostatic induction" during an 1891 lecture at [[Columbia College, Columbia University|Columbia College]].&nbsp; The two metal sheets are connected to a [[Tesla coil]] oscillator, which applies high-voltage [[radio frequency]] alternating current.&nbsp; An oscillating electric field between the sheets [[ionize]]s the low-pressure gas in the two long [[Geissler tube]]s in his hands, causing them to glow in a manner similar to [[Neon light|neon tube]]s.]]

After 1890, inventor [[Nikola Tesla]] experimented with transmitting power by inductive and capacitive coupling using spark-excited [[radio frequency]] [[resonant transformer]]s, now called [[Tesla coil]]s, which generated high AC voltages.<ref name="Shinohara" /><ref name="LeeZhongHui" /><ref name="Tesla1891" >Tesla, Nikola (20 May 1891) [http://www.tfcbooks.com/tesla/1891-05-20.htm   ''Experiments with Alternate Currents of Very High Frequency and Their Application to Methods of Artificial Illumination''], lecture before the American Inst. of Electrical Engineers, Columbia College, New York.  Reprinted as a {{cite book |title=book of the same name by |publisher=Wildside Press |date=2006 |url=https://books.google.com/books?id=94eH3rULPy4C |isbn=978-0809501625}}</ref> Early on he attempted to develop a wireless lighting system based on [[Near and far field|near-field]] inductive and capacitive coupling<ref name="LeeZhongHui" /> and conducted a series of public demonstrations where he lit [[Geissler tube]]s and even incandescent light bulbs from across a stage.<ref name="LeeZhongHui" /><ref name="Tesla1891" /><ref>{{cite book |first1=W. Bernard |last1=Carlson |title=Tesla: Inventor of the Electrical Age |publisher=Princeton University Press |year=2013 |page=132 |isbn=978-1400846559 |url=https://books.google.com/books?id=5I5c9j8BEn4C}}</ref> He found he could increase the distance at which he could light a lamp by using a receiving [[LC circuit]] tuned to [[resonance]] with the transmitter's LC circuit.<ref name="Wheeler" /> using [[resonant inductive coupling]].<ref name="LeeZhongHui" /><ref name="Sun1" /> Tesla failed to make a commercial product out of his findings<ref>{{cite book |first=Christopher |last=Cooper |title=The Truth About Tesla: The Myth of the Lone Genius in the History of Innovation |publisher=Race Point Publishing |year=2015 |pages=143–144}}</ref> but his resonant inductive coupling method is now widely used in electronics and is currently being applied to short-range wireless power systems.<ref name="LeeZhongHui" /><ref name="Leyh">{{cite book |doi=10.1109/NAPS.2008.5307364 |year=2008 |last1=Leyh |first1=G. E. |last2=Kennan |first2=M. D. |title=2008 40th North American Power Symposium |chapter=Efficient wireless transmission of power using resonators with coupled electric fields |pages=1–4 |isbn=978-1-4244-4283-6 |s2cid=3685850}}</ref>

{{multiple image
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| image1   =  TeslaWirelessIllustration.png
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| footer   = ''(left)'' Experiment in resonant inductive transfer by Tesla at Colorado Springs 1899. The coil is in resonance with Tesla's magnifying transmitter nearby, powering the light bulb at bottom. ''(right)'' Tesla's unsuccessful Wardenclyffe power station.
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Tesla went on to develop a wireless power distribution system that he hoped would be capable of transmitting power long distance directly into homes and factories. Early on he seemed to borrow from the ideas of Mahlon Loomis,<ref>{{cite book |first1=W. Bernard |last1=Carlson |title=Tesla: Inventor of the Electrical Age |publisher=Princeton University Press |year=2013 |page=H-45 |isbn=978-1400846559 |url=https://books.google.com/books?id=5I5c9j8BEn4C}}</ref><ref>{{cite book |first=Marc J. |last=Seifer |title=Wizard: The Life and Times of Nikola Tesla : Biography of a Genius |publisher=Citadel Press |year=1996 |page=107}}</ref> proposing a system composed of balloons to suspend transmitting and receiving electrodes in the air above {{convert|30000|feet}} in altitude, where he thought the pressure would allow him to send high voltages (millions of volts) long distances. To further study the conductive nature of low pressure air he set up a test facility at high altitude in Colorado Springs during 1899.<ref>{{cite book |first=Robert |last=Uth |title=Tesla, Master of Lightning |publisher=Barnes & Noble Publishing |year=1999 |page=92}}</ref><ref>{{Cite web |url=https://www.pbs.org/tesla/ll/ll_colspr.html |title=Tesla – Master of Lightning: Colorado Springs |publisher=PBS}}</ref><ref>{{cite book |first1=W. Bernard |last1=Carlson |title=Tesla: Inventor of the Electrical Age |publisher=Princeton University Press |year=2013 |page=264 |isbn=978-1400846559 |url=https://books.google.com/books?id=5I5c9j8BEn4C}}</ref> Experiments he conducted there with a large coil operating in the megavolts range, as well as observations he made of the electronic noise of lightning strikes, led him to conclude incorrectly<ref>{{cite book |first1=W. Bernard |last1=Carlson |title=Tesla: Inventor of the Electrical Age |publisher=Princeton University Press |year=2013 |page=301 |isbn=978-1400846559 |url=https://books.google.com/books?id=5I5c9j8BEn4C}}</ref><ref name="Christopher Cooper 2015, page 165"/> that he could use the entire globe of the Earth to conduct electrical energy. The theory included driving alternating current pulses into the Earth at its resonant frequency from a grounded Tesla coil working against an elevated capacitance to make the potential of the Earth oscillate. Tesla thought this would allow alternating current to be received with a similar capacitive antenna tuned to resonance with it at any point on Earth with very little power loss.<ref>{{cite book |first1=W. Bernard |last1=Carlson |title=Tesla: Inventor of the Electrical Age |publisher=Princeton University Press |year=2013 |pages=209–211 |isbn=978-1400846559 |url=https://books.google.com/books?id=5I5c9j8BEn4C}}</ref><ref name="Tesla1904">{{cite journal |last=Tesla |first=Nikola |title=The Transmission of Electric Energy Without Wires |journal=Electrical World and Engineer |volume=43 |pages=23760–23761 |date=5 March 1904 |url=http://www.tfcbooks.com/tesla/1904-03-05.htm}}, reprinted in ''[https://books.google.com/books?id=qPI5AQAAMAAJ&pg=PA30 Scientific American Supplement, Munn and Co., Vol. 57, No. 1483, 4 June 1904, p. 23760–23761]''</ref><ref name="Sewall">{{cite book |last1=Sewall |first1=Charles Henry |title=Wireless telegraphy: its origins, development, inventions, and apparatus |publisher=D. Van Nostrand Co. |date=1903 |pages=38–42 |url=https://books.google.com/books?id=q_J3qYI5erkC&q=Tesla&pg=PA38}}</ref> His observations also led him to believe a high voltage used in a coil at an elevation of a few hundred feet would "break the air stratum down", eliminating the need for miles of cable hanging on balloons to create his atmospheric return circuit.<ref>{{cite book |first1=W. Bernard |last1=Carlson |title=Tesla: Inventor of the Electrical Age |publisher=Princeton University Press |year=2013 |page=252 |isbn=978-1400846559 |url=https://books.google.com/books?id=5I5c9j8BEn4C}}</ref><ref name="Cooper_1916_110">Cooper, Drury W., internal document of the law firm Kerr, Page & Cooper, New York City, 1916. (Cited in {{cite book |last1=Anderson |first1=Leland |title=Nikola Tesla on His Work with Alternating Currents and Their Application to Wireless Telegraphy, Telephony, and Transmission of Power: An Extended Interview |publisher=Sun Publishing Company |date=1992 |page=110 |url=https://books.google.com/books?id=KRg9HWakBmQC |isbn=978-1893817012 }}</ref> Tesla would go on the next year to propose a "[[World Wireless System]]" that was to broadcast both information and power worldwide.<ref name="Carlson2" >{{cite book |first1=W. Bernard |last1=Carlson |title=Tesla: Inventor of the Electrical Age |publisher=Princeton University Press |year=2013 |pages=302–367 |isbn=978-1400846559 |url=https://books.google.com/books?id=5I5c9j8BEn4C}}</ref><ref name="CenturyMag">{{cite journal |last=Tesla |first=Nikola |title=The Problem of Increasing Human Energy |journal=Century Magazine |date=June 1900 |url=http://www.tfcbooks.com/tesla/1900-06-00.htm |access-date=20 November 2014}}</ref> In 1901, at Shoreham, New York he attempted to construct a large high-voltage wireless power station, now called [[Wardenclyffe Tower]], but by 1904 investment dried up and the facility was never completed.

=== Post-war developments ===

Before World War II, little progress was made in wireless power transmission.<ref name="Brown1984"/> [[Radio]] was developed for communication uses, but could not be used for power transmission since the relatively low-[[frequency]] [[radio wave]]s spread out in all directions and little energy reached the receiver.<ref name="Shinohara" /><ref name="Brown1984"/> In radio communication, at the receiver, an [[amplifier]] intensifies a weak signal using energy from another source. For power transmission, efficient transmission required [[transmitter]]s that could generate higher-frequency [[microwave]]s, which can be focused in narrow beams towards a receiver.<ref name="Shinohara" /><ref name="Brown1984"/><ref name="Curty">{{cite book |last1=Curty |first1=Jari-Pascal |last2=Declercq |first2=Michel |last3=Dehollain |first3=Catherine |last4=Joehl |first4=Norbert |title=Design and Optimization of Passive UHF RFID Systems |publisher=Springer |date=2006 |page=4 |url=https://books.google.com/books?id=uFjpH3Cl7z8C&pg=PA4 |isbn=978-0387447100}}</ref>

The development of microwave technology during World War II, such as the [[klystron]] and [[magnetron]] tubes and [[parabolic antenna]]s,<ref name="Brown1984"/> made some radiative ([[Near and far field|far-field]]) methods practical for the first time, and the first long-distance wireless power transmission was achieved in the 1960s by [[William C. Brown]].<ref name="Shinohara" /> In 1964, Brown invented the [[rectenna]] which could efficiently convert microwaves to DC power, and in 1964 demonstrated it with the first wireless-powered aircraft, a model helicopter powered by microwaves beamed from the ground.<ref name="Brown1984"/>