Cavity magnetron facts for kids

Magnetron with section removed (magnet is not shown)

Complete microwave oven magnetron, with magnet and heatsink

The cavity magnetron is a high-powered vacuum tube that makes microwaves using the interaction of a stream of electrons with a magnetic field. Electrons pass by holes (cavities), and the resonance creates microwaves, like blowing air on a flute creates sound (sound waves) of a certain pitch. The 'resonant' cavity magnetron type of the earlier magnetron tube was invented by John Randall and Harry Boot in 1940. The high power of pulses from the cavity magnetron made centimetre-band radar practical. Shorter wavelength radars allowed the finding of smaller objects. The small cavity magnetron tube made the size of radar sets much smaller so that they could be put into in aircraft and ships used to find submarines. At present, cavity magnetrons are commonly used in microwave ovens and in various radar applications.

Images for kids

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  A similar magnetron with a different section removed. Central cathode is visible; antenna conducting microwaves at the top; magnets are not shown.

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  Obsolete 9 GHz magnetron tube and magnets from a Soviet aircraft radar. The tube is embraced between the poles of two horseshoe-shaped alnico magnets (top, bottom), which create a magnetic field along the axis of the tube. The microwaves are emitted from the waveguide aperture (top) which in use is attached to a waveguide conducting the microwaves to the radar antenna. Modern tubes use rare-earth magnets, electromagnets or ferrite magnets which are much less bulky.

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  Split-anode magnetron (c. 1935). (left) The bare tube, about 11 cm high. (right) Installed for use between the poles of a strong permanent magnet

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  Cutaway drawing of a cavity magnetron of 1984. Part of the righthand magnet and copper anode block is cut away to show the cathode and cavities. This older magnetron uses two horseshoe shaped alnico magnets, modern tubes use rare-earth magnets.

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  9.375 GHz 20 kW (peak) magnetron assembly for an early commercial airport radar in 1947. In addition to the magnetron (right), it contains a TR (transmit/receive) switch tube and the superheterodyne receiver front end, a 2K25 reflex klystron tube local oscillator and a 1N21 germanium diode mixer. The waveguide aperture (left) is connected to the waveguide going to the antenna.

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  Sir John Randall and Harry Boot's original cavity magnetron developed in 1940 at the University of Birmingham, England, now in the Science Museum, London.

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  The electromagnet used in conjunction with Randall and Boot's original magnetron, in the Science Museum, London.

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  The anode block which is part of the cavity magnetron developed by Randall and Boot

See also

In Spanish: Magnetrón para niños