Induction heating is simply speaking, heating by electromagnetic induction. The object that needs to be heated is an electric conductor and the heat produced within it is due to flow of eddy current which is induced by the process of electromagnetic induction via Joules heating. As eddy current passes through the conductor, due to its resistance, heat is generated and this heat is what we know as induction heat.
This induction heating depends upon lots of factors. And one of them is high frequency. Depending upon the heat that is needed and the object in question, the frequency will vary. Thus the desirable frequency will depend upon the conductor too along with the type of material, the arrangement between the conductor and the coil and up to how much penetration of heat is needed. Different frequency will enable the heat to penetrate to a different level and thus one has to ascertain what depth of penetration is needed before determining the frequency of the induction heater.
As the frequency is increased, the depth of penetration by the heat is decreased. Hence the frequency is inversely promotional to the penetration by the heat. So, to increase the penetration, the frequency must be lowered so that heat can penetrate further.
Thus when deep penetration is needed, the extensive cycle of induction heating is used with low frequency. As low frequency enables the heat to travel further or penetrate further, the target of the goal is achieved conveniently. On the other hand, the most amount of energy is transferred in case of induction heating, at high frequency. Thus when the penetration of the heat isn’t a requirement yet, high amount of transfer of energy is desired, induction heating at high frequency is used. And when deep penetration is desired, low frequency with the extensive cycle is used in induction heating.