Karl Ferdinand Braun (6.06.1850-20.04.1918) was a German physicist and a corresponding member of the Berlin Academy of Sciences (1914). He was born in Fulda. He graduated from the University of Berlin (1872). In 1872-74 he worked at the University of Würzburg, in 1874—76 at a gymnasium in Leipzig, in 1876—80 he was professor at the University of Marburg, in 1880 — 83 at the University of Strasbourg, in 1883 —85 at the Higher Technical School in Karlsruhe, and in 1885 —95 at the University of Tübingen, where he founded a physics institute. From 1895 he was professor at the University of Strasbourg and director of the Physics Institute.
His research was in the field of radio engineering and radiophysics. In 1897 he constructed a cathode tube in which the motion of the electrons was controlled by a magnetic field (the Braun tube). It was the first oscillographic cathode-ray tube. In 1898 he invented an oscillatory circuit of considerable capacitance and low damping (the Braun circuit). In 1899—1900 he proposed separating the antenna from the spark gap, which was essential for the development of radio engineering, since a much larger part of the energy stored in the primary oscillatory circuit was then radiated into space. He invented several types of antenna, in particular the loop antenna (1913). For the development of wireless telegraphy he was awarded the Nobel Prize in 1909. He detected (1874) one-way conduction in crystals of certain metal sulfides (zinc sulfide, lead dioxide, carborundum and others).
He created a school of physicists.