Sir John Ambrose Fleming (sometimes also listed as Ambrose J. Fleming), (November 29, 1849 - April 18, 1945) was an English electrical engineer and physicist. He was born John Ambrose Fleming on November 29, 1849 to James and Mary Anne Fleming at Lancaster, Lancashire and baptised on February 11, 1850.
Fleming was born in Lancaster and educated at the University College School, London, and the University College London. He became a Lecturer at a number of universities including the University of Cambridge, the University of Nottingham, and University College London, where he was the first professor of Electrical Engineering. Consultant to the Marconi Wireless Telegraph Company, Swan, Ferranti, Edison Telephone, and later the Edison Electric Light Company. In 1892, Fleming presented an important paper on electrical transformer theory to the Institution of Electrical Engineers in London.
In November 1904, he invented and patented the two-electrode vacuum-tube rectifier, which he called the oscillation valve. It was also called a thermionic valve, vacuum diode, kenotron, thermionic tube, or Fleming valve. This invention is often considered to have been the beginning of electronics, for this was the first vacuum tube. Fleming's diode was a vital unit in radio receivers and radars for many decades afterwards, until solid-state electronic technology took over.
In 1906, Lee De Forest of the USA added a control "grid" to the valve to create a vacuum tube RF detector called the Audion, leading Fleming to accuse him of copying his ideas. De Forest's device was shortly refined by him into an amplifier tube called the triode. The triode was vital in the creation of long-distance telephone and radio communications, radars, and early digital computers.
Fleming also contributed in the fields of photometry, electronics, wireless telegraphy (radio), and electrical measurements. He was knighted in 1929, and he died at Sidmouth in Devon in 1945. His contributions to electronic communications and radar were of vital importance in winning World War II.
Fleming was awarded the IRE Medal of Honor in 1933 for "the conspicuous part he played in introducing physical and engineering principles into the radio art."