Microwave technology matured for the development of radar during the Second World War. When the war was about to end, the American engineers who adjusted the radar found that the chocolate in their pockets often melted! They immediately understood that this was caused by the effect of electromagnetic waves on the material, and it was the same thing as the insulation loss and heat in high-power cables. Curiosity drove them to use microwave devices to make popcorn to succeed. This is the embryonic form of microwave power application equipment. As early as the 1930s, when debugging high-power radio transmitters, flies or insects were often found to die in hollow solenoids. These accidental discoveries clearly revealed to people that both microwaves and radio waves can cause heating and drying. . In fact, both microwaves and radio waves are electromagnetic waves, but the frequency of microwaves is above 300 MHz, while the frequency of radio waves is below 300 MHz. Of course, the early technical focus of the development of radio technology was to use electromagnetic waves of various frequencies to carry information or obtain information in order to construct a modern and colorful life. It is impossible to use expensive radio and radar equipment for heating and drying in the initial stage. The use of radio wave heating as an industrial application, earlier than microwave heating, is called radio frequency heating. With the development of microwave technology, the generated microwave power continues to increase and the cost is reduced. It is possible to convert the energy of the microwave electromagnetic field into the energy of material molecules as a means of scientific research, production and medical treatment. This method of penetrating into the substance and instantly transforming into molecular heat energy has changed the traditional concept of heating from the outside to the inside and created a new technology for rapid heating.
Principle and Microwave Power Application Equipment Microwave electromagnetic waves have two transmission states. The first is to propagate directionally from the antenna to the space, which is straight line propagation like light. The second is the guided transmission state set by man, which restricts the transmission of electromagnetic waves in hollow pipes. Such hollow pipes are called waveguides, which are generally rectangular or circular and made of good conductors such as copper or aluminum. The cross-sectional size of the waveguide is related to the frequency of the microwave used. The microwave electromagnetic wave propagating in the hollow waveguide encloses the energy for transmission. It can be transmitted over long distances with minimal energy loss. If the wave guide is filled with non-metallic substances, resulting in loss of transmission power, the transmission distance is limited. Because of the interaction between the electromagnetic field and the material, part of the energy of the electromagnetic wave has been converted into the energy of the material molecule. The conversion ratio is related to the frequency of the electromagnetic wave and the loss factor of the material. In principle, it is possible to convert all the electromagnetic wave energy introduced into the wave guide into the energy of material molecules. The increase in temperature is the main indicator of the increase in energy of material molecules. Electromagnetic waves propagate at the speed of light, and the speed of electromagnetic waves penetrating into matter is close to the speed of light propagation; and the time to transform the energy of electromagnetic waves into the energy of material molecules is approximately instantaneous, and the conversion time in the microwave frequency band is faster than Ten millionths of a second. This is the principle that microwaves can form internal and external heating at the same time. Traditional heating of solid materials must be in a heated environment, and then gradually introduced into the solid from the surface to the inside to obtain the thermal equilibrium conditions, which requires a long time. The heating environment is generally impossible to be strictly adiabatic and sealed. In a long heating time, it may emit a lot of heat to the environment. The microwave power is in the closed state of all cards, penetrates into the object at the speed of light, and instantly transforms into heat, which saves heat loss during long-term heating. This is the energy-saving principle of microwave heating.
