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FERDINAND Braun. A PIONEER IN WIRELESS technology AND electronics Ferdinand Braun – A pioneer in wireless technologY and electronics Peter Russer n 1909 Ferdinand Braun and Guglielmo Marconi jointly received the Nobel Prize for their groundbreaking contributions to wireless telegraphy. Beyond numerous important contributions to wireless transmitter and receiver cir- cuit technology Ferdinand Braun has given other epoch-making contribu- tions to electronics and wireless technology, including the discovery of the rectifying properties of a metal-semiconductor junction in 1874, the invention of the Icathode ray tube (Braunsche Röhre) in 1897, and precise voltage measurement in- struments. He has given the impact to the foundation of “Hartmann & Braun” and “Telefunken” and had a considerable influence on the industrial development of Ger- man wireless technology. Introduction Ferdinand Braun (1850-1918) has been an extraordinary influential pioneer in wire- less technology who has had a strong impact on the industrial development of that field. He has given three seminal contributions to radio science and electronics: – The discovery of unipolar conduction of metalsemiconductor junctions in 1874 is the starting point from which solid state electronics develops.1 – The invention of the cathode ray tube (Braun’s tube) in 1897 provided for a cen- tury the primary electronic display device for measurement equipment, radar, television and computers.2 – The introduction of coupled resonant circuits in wireless transmitters in 1898 al- lowed to bridge higher distances in wireless telegraphy and has been the precon- dition for Guglielmo Marconi’s success in the first transatlantic wireless trans- mission in 1901.3 © 2009 EUROPEAN MICROWAVE ASSOCIATION (EUMA). REPRINTED WITH PERMISSION, FROM P. RUSSER, “FERDINAND BRAUN – A PIONeeR IN WIRELESS TECHNOLOGY AND ELECTRONICS”, Proceedings of the 39th European Microwave Conference, ROme, ITALY, OCTObeR 2009, PP. 547-554. 1 F. Braun, “Ueber die Stromleitung durch Schwefelmetalle”, Annalen der Physik und Chemie, 229(1875), 12, pp. 556-563, . 2 F. Braun, “Ueber ein Verfahren zur Demonstration und zum Studium des zeitlichen Verlaufes variabler Ströme”, Annalen der Physik und Chemie, 296(1897), 3, pp. 552-559. 3 F. Braun, Drahtlose Telegraphie durch Wasser und Luft (Leipzig, 1901), K.F. Braun, “Electrical oscillations and wireless telegraphy”, in: From Nobel Lectures, Physics 1901-1921 (Amsterdam, 1967), pp. 226-245. 228 FERDINAND Braun. A PIONEER IN WIRELESS technology AND electronics For the third contribution Ferdinand Braun together with Gug- lielmo Marconi received the Nobel Prize in 1909. Giving the initial impulse for the foundation of companies like Hartmann & Braun and Telefunken, Ferdinand Braun has influenced strongly the industrial development of wireless technology in Germany at the beginning of the 20th century. It has been the achievement of Friedrich Kurylo, hav- ing written the first biography of Ferdinand Braun.4 As a reference the later biography of Florian Hars is more reliable.5 Interesting material also can be found in6 and in Georg Schmucker’s biography of Jona- than Zenneck.7 Early life and education Karl Ferdinand Braun was born on 6 June 1850 at Fulda in the Kur- fürstentum [electorate princedom] Hessen as the fourth child of Jo- hann Conrad and Franziska Braun. His father Johann Conrad Braun has been actuary at the district court Fulda. In his teens he attended the Gymnasium [high school] in Fulda, and after completing the Gymnasium he enrolled in courses in mathematics and chemistry at the University Marburg. After two semesters he moved to Berlin where he focused on Physics.8 Professor Georg Hermann Quincke gave him an assistantship at the Gewerbeakademie Charlottenburg. He worked on his PhD under Quincke’s supervision and received his doctor’s degree in March 1872 with a thesis on the oscillations of elas- tic strings from the University Berlin, where Hermann von Helmholtz has been his examiner. The birth of semiconductor electronics In early 1872, when Georg Quincke was appointed as Professor at the University Würzburg, Ferdinand Braun followed him there as an assistant. In Würzburg the research activities of Ferdinand Braun mainly were focused on problems of electric conductivity. In the first 4 F. Kurylo, Ferdinand Braun (Moos, 1965). 5 F. Hars, Ferdinand Braun (1850-1918). Ein wilhelminischer Physiker (Berlin, 1999). 6 G. Wolfschmidt, Von Hertz zum Handy – Entwicklung der Kommunikation (Norderstedt, 2007). 7 G. Schmucker, “Jonathan Zenneck: 1871-1959; eine technischwissenschaftliche Biographie”, Ph.D. dissertation, University of Stuttgart, 1999. 8 Hars, Ferdinand Braun (1850-1918). 229 FERDINAND Braun. A PIONEER IN WIRELESS technology AND electronics of these works he investigated the conductivity of melted salts9 and a second paper dealt with the unipolar electric conduction through gas layers of variable conductivity.10 Ferdinand Braun’s interest in electri- cal conductivity of metal salts led him to the investigation of copper sulfide crystals. In the paper with the title “Ueber die Stromleitung durch Schwefelmetalle” [About the conduction of current through metal sulfides], submitted to Annalen der Physik und Chemie on 23 November 1874, he reported the observation that the electrical re- sistance of various natural and synthetic metal sulfide samples was dependent on direction, intensity and duration of the electrical cur- rent. The disparity of the currents has been up to 30 percent.11 He also observed, that in one direction the electrical resistance increased with decreasing current intensity and that the effect was depending on how the metallic contacts were applied to the metal sulfide sample. These effects could not be explained on the basis of existing theories. Per- forming his experiments accurately and repeatedly he could foreclose any error in measurement. After working two years with Quincke, he accepted in fall 1874 a safe and well-paid teaching appointment to the St. Thomas Gymnasi- um in Leipzig. However, also during his engagement as a Gymnasium teacher he tried to continue his scientific work. In the following, several researchers investigated the unipolar conductivity under different conditions and with other materials and got similar results. Werner Siemens obtained similar results with selenium if both electrodes applied to the crystal differed con- siderably in size.12 Other researchers could not find unipolar con- duction. Braun reacted on this with a paper about the deviations from Ohm’s law in solids with metallic conductivity.13 In this paper he concluded In general the anomalous effects occur in the easiest way if at least one electrode is small. Therefore in the majority of cases I have used as the one electrode a wire which has been pressed by a spiral spring enclosed in a bushing against the crystal. 9 F. Braun, “Ueber die galvanische Leitungsfähigkeit geschmolzener Salze”, Annalen der Physik, 230(1875), 2, pp. 161-196. 10 F. Braun, “Ueber die unipolare Elektricitätsleitung durch Gasschichten von verschiedener Leitungs- fahigkeit”, Annalen der Physik und Chemie, 230(1875), 4. 11 Braun, “Ueber die Stromleitung durch Schwefelmetalle”. 12 W. Siemens, “Ueber die Abhängigkeit der electrischen Leitungsfähigkeit des Selens von Wärme und Licht”, Annalen der Physik, vol. 238, no. 12, pp. 521–550, 1877. 13 F. Braun, “Ueber Abweichungen vom Ohm'schen Gesetz in metallisch leitenden Körpern”, Annalen der Physik, 237(1877), 5, pp. 95-110. 230 FERDINAND Braun. A PIONEER IN WIRELESS technology AND electronics Depending on the steadiness of the material a pressure of up to one kilo has been applied. In other experiments a mercury contact has been chosen. In further experiments the crystal surface has been covered galvanoplastically with a thin copper layer and this has been overlayed with mercury. The effects are mostly, if not always, determined by the junction region. At this place a very considerable current dependent resistance is localized. Thus Ferdinand Braun has discovered the point contact rectifier -ef fect and by this way created the whisker diode. In14 Ferdinand Braun reported experimental investigations of unipolar conduction on psilo- melane, a hard black manganese oxide. For his experiments he used psilomelane plates mounted in a screw clamp, isolated from the clamp, so that only the peak of the clamp exhibited electrical contact to the psilomelane plate. At this time unipolar conductivity has had no technical application, and also the physical laws governing this effect have not been known for the next fifty years. However, with his experiments performed with copper sulfide and other materials Ferdinand Braun has been the first one who has reported rectifying action of a semiconductor barrier. Fer- dinand Braun’s work marks the beginning of solid state electronics.15 He never has applied this effect to realize any device and he never has claimed this, but he has opened a new branch of science, which yielded the first sensitive radio wave detectors twenty years later and today’s semiconductor electronics. The first one who has constructed and applied a semiconductor rectifier for the detection of electromagnetic waves has been Jagadis Chandra Bose, Professor of physics at the Presidency College in Kol- kata, India. He used galena (lead sulfide) crystals contacted by a metal wire to detect millimeter waves. He reported this invention in the April 27, 1899, meeting of the Royal Society, London,16 and filed 1901 a U.S 14 F. Braun,
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