Multi-cavity cavity is also called microwave excitation cavity feed port. It is a very important component in microwave equipment. It determines the good and bad design of microwave equipment from its arrangement and distribution. Â The design of the general professional in this respect is based on the different arrangement of different materials to be heated, which also determines the quality of the microwave equipment . This involves a deeper level of expertise, so let's take a closer look. Â Â Â Â Â
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     First, multi-cavity design: usually due to the commonality of microwave wavelength and object geometry, the microwave single-mode cavity in the S-band has a small geometry and a small volume. This small-volume cavity is not only There is no use value in industrial heating, even in a domestic microwave oven. This has determined that both domestic microwave ovens and industrial microwave ovens have to use over-mode multimode electromagnetic resonant cavities. From the theory of physics and electromagnetism, it is known that in any resonant cavity, in the over-mode state, there may be The number of resonant modes is proportional to the volume of the cavity. In other words, the larger the volume, the more the number of modes that may exist, and the uniformity of the distribution of the microwave electric field in the cavity is proportional to the number of modes. That is why people always want to design a cavity with a large cavity to improve the uniformity of the electric field in the cavity. However, the one-sided pursuit of increasing the volume will reduce the power density of the microwave power under certain conditions. Of course, from the law of conservation of energy, as long as the volume is increased, the metal boundary around the cavity does not increase the loss (such as using ideal or close Ideal for metal materials), even if the power density is reduced, it will not have a significant effect on the heating effect. However, in reality, the conductivity of any metal material is limited, especially stainless steel, and its loss is aluminum. 25 times, is 41 times that of copper, and 44 times that of silver. Therefore, if stainless steel is used as the material of the cavity, it increases the volume and greatly increases the area and loss of the entire cavity wall. In this case, the increase is adopted. The bulky approach is only correct if the microwave input power is increased at the same time. This is the reason why 1kW~1.6kW magnetrons are used in large-volume domestic microwave ovens that are currently exported on the market. In industrial microwave ovens , the volume of the furnace chamber is usually between 500 and 20,000 liters due to the volume factor of the heated material. Sometimes even bigger. In such a large cavity, such as the microwave magnetron of the 915MHz or 2450MHz band as the microwave source, it is obviously working in a large "overmodulation" state, so the number of modes that may exist therein is very large. In this case, as long as the power density is sufficient, the uniformity of the field distribution in the cavity is ideal. The no-load quality factor of the furnace chamber is very high, but once the material to be heated (especially the material with high water content) is added, the load quality factor of the furnace chamber drops sharply, and the degree of decline can reach 3 to 5 An order of magnitude, sometimes not even resonant, a typical high-Q resonant system becomes a low-Q microwave irradiation system.
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     The second factor is the shape and volume of the material to be heated. The choice of furnace cavity size, especially the cross-sectional dimension, is mainly based on the volume and shape requirements of the material. The choice of the length direction should take into account the microwave power and the processing yield. Claim.
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     The third factor is that the volume of the furnace chamber should be selected according to the water content of the material to be heated, especially the dimension in the length direction. The length of the water content can be shorter, otherwise it should be longer.
    The fourth factor is based on the number of feed ports of the microwave source, whether it is a single feed port or a multi feed port, whether it is a single microwave source or a plurality of microwave sources (especially a plurality of microwave sources independent of each other).
    The fifth factor is the magnitude of the power density in the cavity. Too high a microwave power density will result in the following two effects.
  (1) dielectric breakdown of air or gas-vapor mixture in the furnace;
  (2) Excessive internal stress causes damage to the material to be heated.
    In summary, when designing a multi-cavity cavity, we should select reasonable dimensions in theory, especially experimentally, according to the constraints of many mutual constraints, in order to achieve high output with good uniform distribution and high efficiency for safe operation. Industrial microwave oven .
    Finally, it should be pointed out that in industrial microwave ovens, due to the large power, a three-phase full-wave rectification and non-filtering power supply system is usually used. This DC power supply greatly reduces the current ripple of the magnetron, so there is no such thing as a household microwave oven. The multi-frequency output phenomenon of the microwave source caused by the half-wave double-voltage DC power supply. On the other hand, in the industrial microwave oven, a looper is usually connected between the microwave source output and the furnace chamber, so that the load change does not generate frequency and power to the microwave source. Traction phenomenon. These two factors make the performance of the magnetron used in industrial microwave ovens more stable.
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