Triode were invented, Philipp Lenard used the principle of grid control while conducting photoelectric experiments in 1902. The first vacuum tube used in radio was the thermionic diode or Fleming valve, invented by John Ambrose Fleming in 1904 as a detector for radio receivers. It was an evacuated glass bulb containing two electrodes, a heated filament and a plate (anode). Triodes came about in 1906 when American engineer Lee De Forest and Austrian physicist Robert von Lieben independently patented tubes that added a third electrode, a grid, between the filament and plate to control current. Von Lieben's partially-evacuated three-element tube, patented
Harold Rosen (electrical engineer) Harold Rosen (electrical engineer) Harold A. Rosen (March 20, 1926 – January 30, 2017) was an American electrical engineer, known as "the father of the geostationary satellite", and "father of the communications satellite". He formed and led the team that designed and built the first geosynchronous communications satellite, Syncom, for Hughes Aircraft Company. Rosen served in the US Navy as a radio communication and radar technician during World War II. He graduated from Tulane University in 1947 with a Bachelor of Engineering degree in electrical engineering. He received his M.S. (1948) and Ph.D. (1951) in electrical engineering from the California