Dielectric heating by the radio frequency method

After a brief reference to some of the applications of radio-frequency energy to the heating of dielectric materials,the general theory of the method is outlined. The heat and power relations governing all such uses are discussed in some detail with special reference to sources of electrical and thermal loss in the generator and the work. It is shown that, for minimum losses and a reasonably good temperature distribution, fast heating is desirable. A family of curves is included enabling relative performances of various generators in terms of power and time to be rapidly determined. The basic circuits for dielectric heating equipments are briefly reviewed and the need for correct loading of the transmitting valves is explained. Two of the more usual load coupling circuits are analysed so that the effects on loading and efficiency of varying circuit parameters may be studied. It is shown that the series-capacitance type of circuit can, under certain conditions, maintain nearly constant power in the work during a heating cycle. For transformer circuits, the conclusions reached show that a proper value of coupling coefficient is desirable in the interest of circuit efficiency.