Microwave is an electromagnetic wave. Microwave oven consists of power supply, magnetron, control circuit and cooking cavity. The power supply provides a high voltage of about 4 volts to the magnetron. Under the excitation of the power supply, the magnetron continuously generates microwaves, which are coupled into the cooking cavity through the waveguide system. There is a rotatable agitator near the entrance of the cooking cavity. Because the agitator is a fan-shaped metal, it can reflect microwaves in all directions after rotating, so it can evenly distribute microwave energy in the cooking cavity, thus heating food. The power range of microwave oven is generally 5 ~ 1 watts. During the Second World War (1945), Spencer, an American radar engineer, happened to find that the chocolate bar in his pocket melted and sticky when he was doing radar experiments. He suspected that it was caused by his body temperature, and later he discovered the thermal effect of microwave in successive experiments. [1] Taking advantage of this thermal effect, in 1945, the United States issued the first patent for using microwaves. In 1947, Raytheon Company of the United States developed the world's first microwave oven-radar oven. In the 194s, microwave ovens were mostly used in industry and commerce. After people's continuous improvement, the household microwave oven was born in Western Europe in 1955, and began to enter the family in the 196s. In the 197s, due to the solution of radiation safety and operation convenience, the cost of the microwave oven continued to drop, and it was further popularized and used, forming an important family industry, and at the same time, it was continuously improved in variety and technology. In 198s and 199s, the continuous application of control technology and sensing technology made microwave ovens widely popular.