The working principle of microwave oven is: 1. Characteristics of microwave Microwave is an electromagnetic wave with a frequency of 300MHZ~300GHZ. Its wavelength is very short, it has the property of visible light, and it travels along a straight line. Microwave can be reflected when it meets metal materials, can penetrate when it meets insulating materials such as glass, plastic and ceramics, and can be absorbed when it meets media such as protein and fat containing water, and can convert electromagnetic energy of microwave into heat energy. Because of the high frequency of microwave, its transmission needs to be transmitted through a waveguide with high conductivity. Although the frequency band of microwave is very wide, the frequency band really used for microwave heating is very narrow. The main reason is to avoid using more frequencies and prevent interference with microwave communication. There are two frequencies of domestic microwave ovens in the world, 9 15MHz and 2450MHz. 2450MHz is used for household cookers, and 9 15MHz is used for drying and disinfection. ?

2 microwave heating principle The heated medium can be generally divided into nonpolar molecular dielectric and polar molecular dielectric. When there is no external electric field, polar molecules do not show polarity. If this medium is placed in an external electric field, each polar molecule will form an orderly arrangement along the direction of electric field force, and the opposite charges will be induced on the surface of the medium, which is called polarization. The stronger the applied electric field, the stronger the polarization. When the applied electric field changes direction, polar molecules also form an ordered arrangement in the opposite direction.

If alternating electric and magnetic fields are applied, polar molecules will be magnetized repeatedly. The higher the frequency of alternating electric field, the faster the polarization of polar molecules rotates repeatedly. At this time, the kinetic energy of molecular thermal motion increases, that is, the heat increases, and the temperature of food also increases, thus completing the transformation from electromagnetic energy to heat energy. The frequency of household microwave oven is 2450MHz, the direction of electric field changes 2.45 billion times per second, and the heat generated can be imagined. Microwave ovens use microwaves to cook food. The magnetron generates 2450MHz ultra-short electromagnetic waves, which are emitted to all parts of the oven through tiny components. After emission, conduction and food absorption, polar molecules (such as water, fat, protein, sugar, etc. ) vibrates at an extremely high speed of 2.45 billion times per second. Friction caused by vibration makes food produce high heat, thus cooking food.

In the working process of microwave oven, the electric control system converts the AC voltage of 220V into the DC voltage of about 4000V through the high-voltage transformer and high-voltage rectifier, and sends it to the microwave generator to generate microwave, which is introduced into the furnace thermal cavity through the waveguide. Because the furnace thermal cavity is made of metal, microwaves can't pass through. It can only be reflected in the furnace cavity and repeatedly penetrated into the food for heating, thus completing the heating process.