Dielectric heating — Principles and specific features

Electromagnetic radiation at very high frequencies (above 10 MHz) is widely used in telecommunications as a medium for transporting information: television, radar, telephony, computers.

Shortly after the Second World War, electromagnetic waves were used to heat insulating products or products with very poor electrical conductivity. This property was put to good use in numerous industrial applications, using two frequency ranges:

• high-frequency (HF) radiation, with frequencies typically between 1 and 400 MHz. Their wavelengths range from 300 to 0.75 m respectively;

• microwave radiation (MO) with frequencies ranging from 400 to 18,000 MHz, corresponding to wavelengths of 75 cm and 1.6 cm respectively.

Although HF and MO heating systems are based on the same principle, their application technologies are different.

At high frequencies, wavelengths are of the same order or longer than the dimensions of the equipment. Energy is transferred to the products via sets of electrodes. The electric field is generally polarized.

On the other hand, since the wavelength of microwaves is often smaller than the dimensions of the system's equipment, the entire technology is based on the propagation of electromagnetic waves.

Electromagnetic energy is thus dissipated into the product mass, depending on the distribution of the electric field prevailing in the applicator in the presence of the product to be treated.

This type of energy transfer is highly efficient, since we know how to produce very intense electric field distributions, generating high volumetric power densities (up to 10 kW per dm ³ of product).

The Dielectric Heating article is divided into four parts:

• Principles and specific features ;

• Technology ;

• Industrial applications ;

• a documentation booklet [D 5 943].