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EM WAVE EQUATIONS Combine Maxwell Electromagnetic Wave On the History e of Wireless f 600 BC - 1901 Richard A. Formato, PhD, W3AZ Life Senior Member, IEEE: [email protected] © 2015 Chatham Marconi Maritime Center. All rights reserved worldwide. 2015-09-30 1 WIRELESS TIMELINE The “Industrial Revolution” First Battery (Allesandro Volta) Galvani-Volta “Debate” (~20 yrs) Lightning = Electricity (Ben Franklin) “Electricity” coined (William Gilbert) Induction (Faraday) Static Electricity & Magnetism “Electrodynamics” (Andre Ampere) A.D. E&M Theory (Maxwell) “Electric waves” produced/detected B.C. Marconi Creates the Wireless Industry 2 c600 B.C.: Thales of Miletus discovers static electricity & magnetism (lodestone) WIRELESS 1600: Gilbert coins term ‘electricity’ TIMELINE: 1752: Franklin proves that lightning is a form of electricity SOME KEY 1780: Galvani studies electricity in frog's legs EVENTS 1800: Volta develops the first battery (“Pile”) 1820: Oersted discovers magnetic fields can be caused by electricity 1826: Ampère publishes a theory of electrodynamics 1827: Ohm publishes a mathematical theory of electricity 1831: Faraday demonstrates electromagnetic induction 1867: Gauss’ Law Published (formulated 1835) 1870s: Thomas Edison builds a DC electric generator 1873: Maxwell publishes “A Treatise on Electricity and Magnetism” 1880s: Nikola Tesla developed an AC motor 1888: Hertz produces & detects radio waves 1892: Lorentz publishes the theory of the electron (discovered 1896). 1897: Marconi radios 20 miles (Isle of Wight to Poole) The competition: 1858, Transatlantic undersea telegraph cable 3 Communication Before Wireless - 1 Smoke Signals Drums Carrrier Pigeons Semaphores (still used) Delivery (e.g. Pony Express) 4 Communication Before Wireless - 2 BPL Leventhal CC from Bill Burns Undersea Cables in 1901 5 ELECTRICITY’S “GROWTH SPURT” - 1 Stephen Gray (1666-1736) - Sent 150 m on wet hemp, even further on metal - Identified different types of conductors - Discovered the earth to be an electric “reservoir” Gray’s first experiment with different conductors Ben Franklin (1706-1790) - Only one electric “fluid,” but two types: “Positive” and “Negative” - Famous kite experiment: Lightning is atmospheric electricity (1752) - Boy suspended by (insulating) silk cords could be charged and then as a (conducting) body could (electrostatically) attract small objects (pub. 1744 in a German book on Gray’s work) 8 ELECTRICITY’S “GROWTH SPURT” - 2 Pieter van Musschenbroek (1692-1761) - The “Leyden” jar (1746) - Stored electric charge - Finally, portable electricity - Today’s Capacitor - 18th century craze: shocking chains of people! (Abbe Nollet zapped 600 monks in a circle) Charles-Augustin de Coulomb (1736-1806) - Torsion balance (1785) - 1st precise statement on electric force - Coulomb’s Law (1785) Electricity could be carried around in a jar! r 9 VOLTA’S BATTERY: FINALLY, PORTABLE DC ELECTRICITY Volta invited by the French Academy of Sciences to demonstrate the ‘Pile’ to Napoleon (Paris, 1801). Napoleon bestowed on him the title ‘Count.’ Dissimilar metals 10p: Ni-plated steel 2p: 97% Cu Lemon juice electrolyte 11 ELECTRICITY & HEALTH, CURRENT & MAGNETISM John Wesley (1703-1791) - Co-founder Methodist Church - The Desideratum, or Electricity Made Plain and Useful by a Lover of Mankind and of Common Sense (1760) - Electric shock treatment of mental disorders - Genesis of widespread therapeutic use of electricity - Two views: good health requires electric “balance” illness caused by obstructed electric “fluid flow” Hans Christian Ørsted (1777-1851) - Discovery: Electric current creates magnetism - Famous compass needle experiment (1820) - Demonstrated circular magnetic field surrounding straight current-carrying wire Der Geist in der Natur (1854) “The Spirit in Nature” (Ørsted) 12 Four Pieces to the EM Puzzle 1. Gauss’ Law • Electric & Magnetic Flux 2. Ampere’s Law • Steady-state Current & Magnetic Field 3. Faraday’s Law of Induction • Varying Magnetic Field → Electric Field 4. Maxwell’s Displacement Current • Varying Electric Field → Magnetic Field 13 James C. Maxwell (1831-1879) – 1 • Age 18, two papers at the Royal Society of Edinburgh - On the Equilibrium of Elastic Solids; Rolling Curves • Age 24, presented On the Transformation of Surfaces by Bending (1854) • Age 29, published On the stability of the motion of Saturn's rings (1859) showing rings composed of individual particles (verified by spacecraft Voyager flybys in the 1980s!) • Published the seminal paper in Control Theory, On Governors http://www.edinphoto.org.uk • On reciprocal figures, frames and diagrams of forces (1870) [rigidity of lattices] • Textbooks Theory of Heat (1871) and Matter and Motion (1876) • Introduced statistical analysis in physics • Maxwell-Boltzmann Distribution (kinetic theory of gases) • Introduced Dimensional Analysis in physics (1871) • Developed the Color Triangle (four parameters: hue, intensity, brightness, tint) • Published On the Theory of Colour Vision; developed first durable color photograph. • On the anniversary of Maxwell’s 100th birthday, Einstein said his work was the “most profound and the most fruitful that physics has experienced since the time of Newton.” 18 James C. Maxwell - 2 - Quintessential theoretician (Faraday experimented in a lab, Maxwell in his head) - Used mechanical analogies and imagined being inside the machine (“Gedankenexperiment”) - Philosophically a world apart from Michael Faraday - One of the world’s most influential scientists On Physical Lines of Force (1861) A Dynamical Theory of the Electromagnetic Field (1865) in which he wrote “The agreement of the results seems to show that light and magnetism are affections of the same substance, and that light is an electromagnetic disturbance propagated through the field according to electromagnetic laws.” The complete EM theory in a seminal book: A Treatise on Electricity and Magnetism (1873) • relationships: electric/magnetic fields, electric charge, electric current LAST • introduced a radical new idea, Displacement Current → Electromagnetic Waves PIECE 19 EM WAVE EQUATIONS Combine Maxwell Eqs. Electromagnetic Waves 1 2E 1 2B 2E 0 2B 0 c2 t2 c2 t2 In free space the wave propagates at a constant speed 1 c 0 0 the Speed of Light, 2.99792458 x 108 meters/sec (186,282.397 miles/sec). 21 AT LAST – EM WAVES IN THE LAB! Heinrich Hertz (1857-1894) - Series of experiments 1886-1889 - Credited with creating and receiving EM waves - 1m Cu wires with 30cm Zn spheres ~100 MHz - Christmas Eve 1887: Hertz realized that he had produced and received an electromagnetic wave “It’s of no use whatsoever… just an experiment that proves Maestro Maxwell was right. We just have these mysterious electromagnetic waves that we cannot see with the naked eye. But they are there.” 22 Hmmm… USELESS? NOT QUITE… EVERY PORTION OF THE EM SPECTRUM IS USED IN TODAY’S TECHNOLOGY! Scientific American Magazine 23 From “The Long Road to Maxwell’s Equations,“ James C. Rautio, IEEE Spectrum Magazine, Dec. 2014. 24 MARCONI CREATES THE WIRELESS INDUSTRY - 1 Guglielmo Marconi (1874-1937) - Son of Giuseppe Marconi and Annie Jameson Marconi - Mother was daughter of Andrew Jameson, owner Jameson Irish Whiskey Distillery - Annie & Giuseppe eloped because her family objected, but over time Annie regained good relations which was important in Marconi’s commercial success - Guglielmo was mostly home schooled (Annie was Protestant and uncomfortable with Italy’s Catholic school system) - Marconi was enthralled by stories about Michael Faraday and Ben Franklin (books in the family library) - Age 13, constructed a Lightning Detector (1887) Wireless lab aboard Yacht Elettra, 1923 26 MARCONI CREATES THE WIRELESS INDUSTRY - 2 - Tutored in experimental physics by Prof. Vincenzo Rosa - Annie arranged visit to Professor Augusto Righi (University of Bologna) who appointed Guglielmo as lab assistant (age 17) - Righi’s article on Hertz’s experiments cemented Marconi’s interest in wireless - Marconi made many improvements to Righi’s spark apparatus and became an accomplished experimentalist (i.e., ‘engineer’) - Age 20, built wireless telegraph system using his own design for the spark gap transmitter/receiver and adding a Morse Code key/printer - Reproduced Franklin’s Kite Experiment which later influenced his development of much better wireless antennas - Discovered that increased antenna height improved range outdoors and that grounded vertical antennas worked best 27 The ‘COHERER’ Detector Branly Effect: metal filing-filled tube exhibits very high resistance (MΩ) due to surface oxidation. External disturbance → resistance drops to only a few ohms. Mechanical shock → restores the initial high resistance . Popov’s Coherer Lightning Detector, mid-1890’s? Branly’s Experiment Nov. 1890 (IEEE History of Communications, Sept. 2009) Marconi’s range: • mid-1895, 1600m • mid-1896, 2400m [with TX/RX gnd ] Marconi’s 1896 Receiver Marconi’s Improved Coherer 28 MARCONI CREATES THE WIRELESS INDUSTRY - 3 - Marconi methodically extended his communication range • At first, room-to-adjacent-room in the family home • Earliest outdoor tests in 1895 over 100’s of meters using his new antenna • Family physician and parish priest so impressed they together with Marconi’s parents composed a letter Marconi and his apparatus in England, 1901 to the Italian Ministry of Posts • The response was encouragement for maritime use but nothing more, whereupon Marconi turned to England: (i) the world’s dominant maritime power; (ii) Annie’s influential family connections might help • Guglielmo and Annie set off to
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