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) him with hands-on experience with radio communications and the then-new field of radars. In 1949, Rosen married Rosetta, and they had two sons, Robert (born 1950) and Rocky (born 1966). Rosetta died in 1969. In 1984 he married Deborah Castleman, a satellite systems engineer also working at Hughes Aircraft Company. Rosen died on January 30, 2017 due to complications from a stroke, aged 90. Rosen has more than 80 patents. He was a Fellow of the IEEE and the AIAA, and a member of the National Academy of Engineering. Rosen has received numerous awards which include: Harold Rosen (electrical engineer)