The insulating material is heated by a high frequency electric field. The main heating object is a dielectric. The dielectric is placed in an alternating electric field and is repeatedly polarized (the dielectric exhibits an equal amount of opposite polarity charges on the surface or inside under the action of an electric field), thereby converting electrical energy in the electric field into thermal energy.
The frequency of the electric field used for heating the medium is high. In the medium, short wave and ultrashort wave bands, the frequency is several hundred kilohertz to 300 megahertz, which is called high frequency medium heating. If it is higher than 300 megahertz and reaches the microwave band, it is called microwave medium heating. Usually, the high frequency medium heating is performed in an electric field between the two plates; and the microwave medium heating is performed in a waveguide, a resonant cavity or a radiation field irradiation of the microwave antenna.