Low microwave frequencies can be produced using electron tubes or transistors. High and very high frequencies (>100 MHz) are produced by klystrons, magnetrons or traveling wave tubes.

In decomposition instruments, microwaves are produced using magnetrons.

Operating
Principle
Magnetron

A magnetron is a metallic vacuum tube, consisting of a cathode and an anode, which is surrounded by a permanent magnet frame.

High voltage is applied to a heated rod (cathode) to emit electrons. These electrons are drawn into a circular path by the applied magnetic field. These electrons hit the outer wall of the tube (anode), which is cut at regular intervals radially to the chamber (resonator). Within these incisions the polarity of the electrical field reverses with the desired frequency and produces microwaves. These are emitted via an antenna, e.g. in the microwave oven.