Prospects for the Development of Microwave Power Applications in the New Century

- May 08, 2019 -

< P > Henan Microwave Equipment Network News: Microwave technology was developed for the development of radar during the Second World War. When the war came to an end, American radar engineers found that the chocolate in their pockets often melted! They immediately understood that this was caused by electromagnetic waves acting on substances, and that it was the same thing as heating dielectric loss in high-power cables. Curiosity drove them to succeed in making popcorn with microwave devices. This is the prototype of microwave power application equipment. As early as the 1930s, when debugging high-power radio transmitters, it was often found that flies or insects died in hollow solenoids. These incidental discoveries clearly inspired people that microwave and radio waves can cause heating and drying. Actually, both microwave and radio waves are electromagnetic waves, but the frequency of microwave is above 300 MHz, while the frequency of radio wave is below 300 MHz. Of course, the focus of the early development of radio technology is to use various frequencies of electromagnetic wave to carry information or obtain information in order to construct a modern colorful life. It is impossible to use expensive radio and radar equipment for heating and drying in the initial stage. Radio wave heating as an industrial application is earlier than microwave heating, which is called radio frequency heating. With the development of microwave technology, the microwave power generated is increasing and the cost is decreasing. It is possible to transform the energy of 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 interior of a substance and instantly converting it into molecular heat energy has changed the traditional concept of heating from surface to interior, and created a new technology of rapid heating. Microwave heating principle and microwave power application equipment microwave electromagnetic wave have two transmission states. The first is directed by the antenna to space, which, like light, travels in a straight line. The second is the artificial guided transmission state, which restricts the transmission of electromagnetic waves in hollow pipes, which are called waveguides, usually rectangular or circular, and are made of good conductors such as copper or aluminium. The cross-section size of the waveguide depends on the frequency of the microwave used. The microwave electromagnetic wave propagating in the hollow waveguide tube is to transmit energy in a closed way. It can be transmitted over long distances with minimal energy loss. If the waveguide is filled with non-metallic material, the transmission power will be lost and the transmission distance will be limited. Because of the interaction between electromagnetic field and substance, part of the energy of electromagnetic wave has been transformed into the energy of substance molecule. The conversion ratio is related to the frequency of electromagnetic wave and the loss factor of substance. In principle, all the energy of electromagnetic wave introduced into the waveguide can be transformed into the energy of material molecules. The increase of temperature is the main sign of increasing energy of matter molecules. Electromagnetic wave propagates at the speed of light, and the speed of penetration of electromagnetic wave into matter is similar to that of light. The time of converting the energy of electromagnetic wave into the energy of matter molecules is almost instantaneous, and the time of conversion in microwave frequency band is faster than one millionth of a second. This is the principle that microwave can form both inside and outside rapid heating at the same time. Traditional heating of solid materials must be in a heating environment, and then from the surface to the inside, gradually conducting into the solid interior, to obtain the condition of thermal balance, which takes a long time. Heating environment, generally not very strict adiabatic closure, in a long heating time, it may emit a lot of heat to the environment. The microwave power is all brand closed state, infiltrating into the object at the speed of light, instantly transforming into heat, which saves the heat dissipation in the long heating process, which is the energy-saving principle of microwave heating. The characteristics of

microwave heating compared with RF heating are as follows: (1) microwave power source (2) application (3) waveguide element and feed structure (4) sensing and control. The microwave power source of

generates microwave power is usually driven by magnetron, in which the hot cathode emits electrons and the electrons move in a circular direction under the action of a strong constant magnetic field. The resonant cavity inside the magnetron decelerates the electrons, so that the kinetic energy of the electrons can be transformed into the energy of the electromagnetic wave, accumulated in the resonant cavity, fed into the waveguide tube, and then fed into the application for use. Magnetron needs DC high voltage power supply, filament heating power supply and constant magnetic field coil power supply, and needs corresponding protection and control circuit to form the whole microwave power source. The output of microwave power can be controlled by the excitation current of DC high voltage or constant magnetic field. Microwave applicator is an expanded waveguide tube, which is used as the place where electromagnetic waves interact with matter. The design considerations are to meet the shape and processing requirements of the processed materials, which can be divided into traveling wave type and resonant type. The waveguide element is the connecting part between the microwave power source and the applicator, in order to solve the problem that not only the magnetron can get the best load working condition, but also the applicator can get the effective feeding effect. Considering from the point of view of microwave technology, the waveguide element is accomplished through a variety of waveguide elements and feeding structures. At the same time, the waveguide element provides the number of incident power and overflow reflection power. According to. Sensor configuration is to detect the extent of field and material action, whether it meets the processing needs, such as temperature sensing and humidity sensing. According to the real-time sensing data and the real-time working state of the microwave power source, the device can effectively control the output and transmission speed of the power source. It is necessary to divide microwave power application equipment into four parts. Generally speaking, application equipment is single-piece production or small-batch production, which must be designed according to specific use requirements. It is a process similar to "tailoring". Microwave power application equipment is divided into four parts. Microwave power source and waveguide components are microwave engineering design, sensing and control engineering design. These three parts have strong universality and are not changed by different application objects. Over the years, we have strengthened the standardization and serialization of these three parts, improved the reliability and stability of these components, provided a strong basis for the reliability of the whole machine, and shortened the development cycle of the whole machine. The design of microwave applicator has strong pertinence. It is a multi-disciplinary engineering design because of different processing requirements, different states, shapes and sizes of application objects. In recent years, we have adopted the design method of microwave applicator series. Different departments adopt specific general components to assemble, which reduces the newly designed components to very few, thus further shortening the equipment. The development cycle ensures the reliable quality of the equipment.

2. The present situation of microwave power application in China in the early 1970s, we paid attention to the development of microwave power application technology abroad. As early as at the end of 1972, the Ministry of Electronics Industry held a seminar on microwave tube technology at Nanjing 772 Power Plant (Sanle Electric Corporation). It focused on the possible development of microwave tube applications in new fields, such as industrial applications of microwave heating and drying, microwave therapy, microwave diagnosis and microwave plasma. The development of high power continuous wave magnetron is the precursor of the research work in new fields. In that year, 772 plant began to develop 915 MHz and 450 MHz continuous wave magnetrons. On the basis of the successful development of two bands of continuous wave magnetrons, the first 2450 MHz microwave physiotherapy instrument and 915 MHz microwave heating equipment were developed. The first microwave heating equipment was exhibited in Beijing in the spring of 1974. The phenomenon of rapid microwave heating attracted widespread attention from the industry. In November 1974, the Ministry of Electronic Industry held a symposium on the application of microwave energy technology in Nanjing 772 Plant. The application of microwave power abroad in industrial production, agricultural production and medical treatment was introduced, and the prospect of development in China was discussed. After more than 20 years of efforts, China has initially established the foundation of microwave power application in this field. The microwave power equipment developed by 772 Factory has been firmly established in food, wood and bamboo products processing, pharmaceutical, paper products, wine-making, rubber, chemical and other industrial production, improved production conditions, improved product quality, and developed a variety of microwave plasma equipment. Microwave high temperature equipment and microwave vacuum drying equipment have become an important means of scientific research in many disciplines.

As far as the national situation is concerned, the popularization of microwave power application technology in China has been a very arduous journey for more than 20 years. At present, preliminary achievements have been made and the foundation for further development has been laid. The main signs of this foundation are: (1) Microwave heating and drying, microwave food processing, microwave sterilization and insecticide have been widely used in various industries; (2) Household microwave ovens have formed regulations. The ability of mould production; (3) The clinical application of microwave medical instrument has achieved universal success; (4) At present, many frontier subjects in many fields, using microwave power as a powerful tool, have made many gratifying progress and expanded research positions in new fields, which has kept up with the pace of the world

3. Microwave power applications are moving towards high-tech fields from the perspective of research trends around the world. The application is in the period of developing to a new field, that is, the focus of research has shifted from traditional heating and drying, food processing to many high-tech fields, as a new tool for research work. The main fields are: microwave catalytic chemical reaction, microwave processing of new materials, and the research of various applications of microwave gas discharge. The experimental study of microwave chemistry covers almost all fields of chemistry and chemical industry. A large number of selected reports show that microwave electromagnetic field can accelerate chemical reaction and shorten the reaction time to one tenth to one thousandth of the original time, which brings an attractive prospect to chemical industry. Microwave high temperature technology can sinter fine ceramics, weld ceramics, and process and process materials, such as thermal setting of polymer materials, heat treatment of non-metallic materials. Microwave method is superior to conventional methods. Microwave gas discharge, i.e. low temperature plasma formed by microwave electromagnetic field, is one of the main aspects of microwave power applications. Microwave plasma chemical vapor deposition (MPCVD) and plasma etching are the main methods of microelectronics processing. The preparation of diamond films and optical fibers also adopts MPCVD method, the preparation of ultrafine powder and microwave plasma method, which have many advantages. In microwave plasma, the activity of many particles is stronger than that of radio frequency plasma, so it is more advantageous for chemical reaction and material treatment. In addition, strong illumination light source (such as sulfur lamp) and microwave odor generator, which are composed of microwave electrodeless discharge, are likely to be industrialized step by step. According to preliminary research, the research hotspots in the new field of microwave power in China can be listed as follows: (1) The research of microwave beneficiation (microwave-assisted pyrolysis) has achieved laboratory results in the conversion of sulfides from non-ferrous metals to oxides, of nickel carbonate to nickel oxide, of gold ore desulfurization and of nitrates from radioactive isotopes to oxides. (2) Microwave-assisted organic and inorganic chemical reactions have done a lot of laboratory work to improve the chemical reaction rate. (3) Study on microwave-assisted extraction technology. Microwave electric field can accelerate the dissolution rate and improve the solubility, which has achieved remarkable results in many laboratories. Microwave-assisted extraction

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