ABSTRACT
Radio-frequency (RF) heating systems operating in the industrial, scientic, and medical (ISM) frequency bands have been used over 40 years for processing a variety of materials (Metaxas, 1996; Roussy and Pearce, 1995). The majority of processing installations in industry use variants of the basic class C oscillator circuits as shown schematically in Figure 8.1. Power at the operating frequency is generated at the tank circuit, which is driven by the input energy, with the triode or tetrode valves acting as synchronous switches. The power is usually fed into the applicator via an inductive coupling. The applicator contains the material to be processed, and it is the interaction of the electromagnetic elds, which are generated by the RF oscillator and transferred inductively to the applicator, that is crucial in obtaining optimum performance of the coupled system. A malfunction will result in low operating efciency and the establishment of excessive voltages in the applicator, which may, given favorable circumstances, lead to coronas and/or arcing. It is also very important to consider the combined system rather than just the applicator in isolation.
