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The obsolete thermionic diode is a vacuum tube with two electrodes, a heated cathode and a plate, in which electrons can flow in only one direction, from the cathode to the plate. Among many uses, diodes are found in rectifiers to convert alternating current (AC) power to direct current (DC), demodulation in radio receivers , and can even be ...
Thermionic emission is the liberation of charged particles from a hot electrode whose thermal energy gives some particles enough kinetic energy to escape the material's surface. The particles, sometimes called thermions in early literature, are now known to be ions or electrons .
The thermionic diode was later widely used as a rectifier — a device that converts alternating current (AC) into direct current (DC) — in the power supplies of a wide range of electronic devices, until beginning to be replaced by the selenium rectifier in the early 1930s and almost completely replaced by the semiconductor diode in the 1960s ...
This is a list of vacuum tubes or thermionic valves, and low-pressure gas-filled tubes, or discharge tubes. ... 2 – Diode; 3 – Triode; 4 – Tetrode; 5 – Pentode;
Before thermionic valves were invented, Philipp Lenard used the principle of grid control while conducting photoelectric experiments in 1902. [4] The first vacuum tube used in radio [5] [6] 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 ...
In 1904, working for the Marconi company to improve transatlantic radio reception, Fleming invented the first thermionic vacuum tube, the two-electrode diode, which he called the oscillation valve, for which he received a patent on 16 November. [12] It became known as the Fleming valve.
A thermal diode in this sense is a device whose thermal resistance is different for heat flow in one direction than for heat flow in the other direction. I.e., when the thermal diode's first terminal is hotter than the second, heat will flow easily from the first to the second, but when the second terminal is hotter than the first, little heat will flow from the second to the first.
All practical thermionic converters to date employ caesium vapor between the electrodes, which determines both the surface and plasma properties. Caesium is employed because it is the most easily ionized of all stable elements. A thermionic generator is like a cyclic heat engine and its maximum efficiency is limited by Carnot's law.