The insulating material is heated by high frequency electric field. The main heating object is dielectric. When the dielectrics are placed in the alternating electric field, they will be polarized repeatedly (under the action of electric field, the same amount of opposite polarity charges appear on the surface or inside of the manufacturer of cast aluminium heating plate), thus transforming the electric energy in the electric field into heat energy.

The electric field frequency used in medium heating is very high. In the medium, short and ultra-short wave bands, the frequency is several hundred kilohertz to 300 MHz, which is called high-frequency dielectric heating. If it is higher than 300 MHz and reaches the microwave band, it is called microwave dielectric heating. Usually the high frequency dielectric heating is carried out in the electric field between the two plates, while the microwave dielectric heating is carried out in the waveguide, resonant cavity or under the radiation field of the microwave antenna.

When dielectrics are heated in high frequency electric field, the electric power absorbed per unit volume is P=0.566 fE_rtg_x 10 (W/cm).

If expressed in terms of heat, then:

H = 1.33fE epsilon RTG Delta *10 (cards/seconds.cm)

In the formula, f is the frequency of high frequency electric field, e r is the relative dielectric constant of dielectric, e is the dielectric loss angle, and E is the electric field strength. The formula shows that the power absorbed by dielectrics from high frequency electric field is proportional to the square of electric field strength E, the frequency f of electric field and the loss angle of dielectrics. E and F are determined by the applied electric field, while e r depends on the properties of the dielectric itself. Therefore, the object of medium heating is mainly the material with high dielectric loss.