Microwave Magnetron
The magnetron tube is considered as the heart of a microwave oven. It is the main part of the high voltage system that generates the microwave energy needed to cook the food.
This can be attained by stepping up the AC line voltage and then converted to a DC voltage and then changed to RF energy that is responsible for the cooking process.
The main purpose of the magnetron is to produce the microwave energy of 2450MHz that can cook the food. It is classified under the group of diode electron tube because like an ordinary electron tube, it has no grid.
There is a magnetic field that is enforced between the negative plate called the anode and the positive plate called the cathode serves as the grid.
Structure of Microwave Magnetron
The basic internal structure of the magnetron is composed of:
- The cathode or the filament
- Anode
- Magnets
- The antenna.
The cathode (filament) is also termed as the heater and is located on the center of the magnetron. It is supported and maintained by fixed and large filament leads that are sealed carefully into the tube.
The anode (plate) has a shape of a hollow cylinder of iron and has anode vanes of even numbers are extending inward. The open areas in trapezoidal shape between reach of these vanes are termed as the resonant cavities and has the purpose of a tuned circuit and decides the output frequency that is generated by the tube.
The antenna part is a loop that is linked from the anode to one of the cavities. It is matched to a hollow enclosure of metal called the waveguide into which it transmits the radio frequency energy.
Lastly, the magnetic field is supplied by permanent strong magnets and is mounted around the area of magnetron so that it is parallel to the axis of the cathode.
Operation Theory of Microwave Magnetron
The basic theory of magnetron operation is simple. It is established on the motions of free electrons under the joined influence of magnetic and electric fields.
In order for the magnetron tube to operate, these electrons need to flow from cathode to anode.
The effects of the magnetic field can then be illustrated in a simple way.
There are two permanent magnets that are located below and above the magnetron tube.
Let’s assume that the upper magnet is the North Pole. From here, the lower magnet is the South Pole and is located beneath the page, and the magnetic field is appearing to be coming through it.
The electrons then start flowing through a conductor, producing a magnetic field building up around that conductor.
On the left side of the electron’s path, this magnetic field that is induced in it gives an addition to the permanent magnet that surrounds it.
On the right side of its path, has the opposite effect of deducting from the permanent magnet field.
This has the tendency to weaken the magnet field on the right side and the electrons are bending towards that direction that can result in the circular motion of its travel going to the anode.
This process started when the low voltage is applied to the filament that causes it to heat up. As described earlier, the filament is also considered as the cathode.
The rise in the temperature causes the increase the molecular activity in the cathode and later it generates a force that caused emission of electrons.
Electrons that are leaving on the surface of the heated filament can be compared to as the molecules of the steam that is leaving in the surface of boiling water.
It does not evaporate like the steam but electrons just float over the surface of the cathode, waiting for the impelling force to attract it.
Semiconductors Company
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