Problems in the Design of High-Frequency Heating Equipment

Although some of the first high-frequency power generators which were used for industrial-heating purposes were merely converted radio transmitters, it was found, as the art progressed, that the problems involved were quite peculiar to the industrial class of service. Probably the greatest problem facing the designer of industrial radio-frequency generators is that of the coupling circuit through which the generated power is fed into the load. Various coupling schemes are discussed and the advantages and disadvantages of each are pointed out. A simple analysis of a transformer-coupled circuit is made by showing how the inherent Q of the load is reflected into the tank circuit. The advantages of close coupling are compared with those of loose coupling, and it is suggested that a generator can be made more versatile if low-impedance tank circuits are employed.