Sir John Turton Randall, FRSE, built the first multi-cavity magnetron in conjunction with co-workers for the American and British radar installations during World War II. In 1940, Harry boot manufactured the prototype for working, containing a valve producing microwave radio pulses with a 10cm-wavelength.
The magnetron works by regulating electromagnetic waves’ emission through vibrations. This device works like whistles, whereby instead of controlling sound vibrations, it holds magnetic pulses. While adjusting the level of magnetron tube’s power level, Spencer accidentally discovered the microwave heating capacity therein.