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Design and function
2016-03-10 / DIS 184_58300000140186_ara_en_k
Copyright by BSH Hausgeräte GmbH
Page 27 of 181
3.11
Magnetron
3.11.1
Construction of the magnetron
The magnetron is an electron tube. To be more precise, it is a vacuum velocity-
modulated tube used to generate electromagnetic waves in the microwave range.
The main components of the magnetron are the anode, cathode, permanent
magnets, antenna and electrical connections.
Fig. 24:
Construction of the magnetron
1
Anode
5
Antenna
2
Anode segments
6
Insulating bushes
3
Cathode (heated)
7
Reactance coil
4
Permanent magnets
The cathode is located in the centre of the magnetron. This is either an indirectly
heated, cylindrical hot cathode or the filament itself (so-called directly heated
cathode).
The cathode is enclosed by a solid, cylinder-shaped anode block (usually made
of copper). Frequency-determining cavity resonators are located on the inside of
the anode block. These are usually radial slits that run parallel to the filament and
which are open in the direction of the central hole of the anode block. The anode
segments face from the anode to the cathode. Cooling fins on the outside of the
anode block allow cooling by means of a fan.
The antenna is connected to an anode segment.
The insulating bushings for the cathode pole and antenna comprise insulating
ceramic parts.
Fig. 25:
Cross-section of anode
1
Anode
4
Anode segments
2
Cavity resonator
5
Antenna
3
Cathode
3.11.2
Function of the magnetron
The function of a magnetron can be traced back to that of an oscillating circuit.
Microwaves are generated by simultaneously applying two voltages to the poles.
•
Approx. 3.3 V alternating current at the cathode connections (filaments)
•
Approx. 4 kV as a positive wave of an alternating current at the anode
connections
The high-frequency electromagnetic oscillations (microwaves) generated by the
oscillating circuit (magnetron) are transmitted into the cooking compartment by the
antenna and by means of a waveguide.