# Induction heating: fundamentals

## Principle

In all electric conducting bodies placed within a time-varying magnetic field induced currents (eddy currents) occur. The presence of these induced currents is responsible for the increase of the body temperature as a result of Joule effect.

As to the induction heating processes, the temperature increase of the part to be heated depends on the characteristics of the source current, which generates the time varying magnetic field.

Indeed:

• the amplitude of the source current sets the value of the induced currents, as well as the level of the power dissipated by Joule effect, respectively; consequently, the heating velocity is more or less important, depending on the amplitude of the current source
• the frequency of the source current sets the penetration depth of the electromagnetic field into the part, and consequently the thickness of the volume where the induced currents are developed. The fact that the induced currents are of non-negligible value only in one layer at the surface of the heated part, whose thickness is the penetration depth, is known as skin effect. In function of the value of the penetration depth, the induction heating is more or less localized . In case of high values of the penetration depth compared with the diameter or the thickness of the part, we talk about volume induction heating, while in case of small values, we have a surface induction heating

## Device

In practice, an induction heating device comprises the following main components:

• an inductor, which generates the source field
• a charge, which stands for the part to be heated

## Main parameters

There are several parameters which must be taken into consideration for a high efficiency of the induction heating, viz. to ensure the transfer of the most part of the energy received by the inductor to the work piece to be treated:

• the type of the inductor (geometry, material of the inductor turns, technology)
• the position of the inductor with respect to the charge (magnetic coupling between the source currents and the induced currents)
• the value of the supply frequency and the skin effect characterizing the distribution of the induced currents in the part to be heated
• the magnetic (relative permeability), electric (resistivity) and thermal (conductivity and specific heat) properties of the material of the part to be heated, properties varying mostly with the temperature