What is the magnetron of the microwave oven and how does it works?

The magnetron can be divided into continuous wave magnetron and pulse magnetron. The former is mainly used in household microwave oven, medical microwave therapy machine, scalpel and other small instruments; the latter is mostly used in military equipment such as radar transmitters.

This section mainly introduces the functional characteristics, working principles  of the continuous wave force air-cooled magnetron used in the microwave oven.

Functional characteristics

The function of the continuous wave magnetron is to convert the mains into microwave to heat the food or to treat the patients under the control of the control device, surgery and Disinfection. The continuous wave magnetron has the characteristics of high efficiency, small size, light weight, strong anti-overload ability, small microwave leakage, small volume and small external interference, its service life is more than 1000 hours, no need to heat ( cold start ) when working.

working principles

 The basic structure of the continuous wave magnetron is mainly composed of a cathode ( filament ), an anode, an annular magnetic steel, a coupling ring, a microwave energy output device ( that is, an antenna ), a radiator and a filament plug.The anode of the magnetron is cylindrical, usually made of copper, and the anode is divided into more than ten fan-shaped spaces, each of which is an anodic resonator. The frequency of the resonant frequency, the frequency of the magnetron, is about 2450MHz. A pair of ring permanent magnet steel is embedded in the anode shell, and the magnetic field formed by the magnetic steel is used to control the microwave oscillation energy in the anode cavity. The microwave energy output from the anode is transmitted to the antenna through a ring metal tube, that is, the coupling loop, and then the microwave is sent by the antenna.

The power supply of continuous wave magnetron is supplied by high voltage transformer, high voltage rectifier diode and high voltage capacitor.

The voltage of the filament of the magnetron is AC 3.3V and current 10A. The cathode voltage is about 40V. When the magnetron is energized, the filament is heated and the high voltage electric field is formed between the anode and the anode. Under the action of an electric field, the cathode emits electrons into the anode, and the anode receives the anode current generated by the electrons. When electrons reach each fan-shaped anode resonant cavity, the electron oscillates at its resonant frequency.

At the same time, the constant magnetic field produced by the circular magnetic steel is perpendicular to the direction of the high voltage electric field. Under the action of the magnetic field, the electron moves along the circumferential space between the cathode and the anode, forming a rotating electron cloud of accumulating energy, when the rotation speed is synchronous with the high frequency electromagnetic field, the energy of the electron is transmitted to the high frequency electromagnetic field, which maintains high frequency oscillation and outputs the microwave through the high frequency output device.

The size of the microwave energy depends mainly on the anode voltage and the strength of the magnetic field. Because of the constant magnetic field intensity of the ring magnetic steel, the output power of the microwave is mainly related to the anode voltage. However, if the magnetic steel is broken down or the magnetic decay is obvious, the output power of the magnetron will be reduced, and the heating effect of the microwave oven is worse, the heating is slow, and the fire is insufficient.

The operation of the microwave oven is unstable because of the fluctuation of the power supply voltage, so the anode voltage of the magnetron is usually provided by a power circuit composed of leakage inductance transformer. It can stabilize the anode current of the magnetron and keep the output power of the microwave stable.

Because of the high power consumption and high temperature control, the cooling fan should be set up, and the forced air cooling of magnetron can be dissipated to prevent overheating damage.