Dielectric Heating System Working and Its Applications

The invention of ways to cook food and use fire had played a great role in the evolution of human beings. We have learned to use fire to cook, to melt metals, for production processes in industries, etc. But the greatest breakthrough came when we invented ways to do the same things without using fire. With the course of time and developing technologies, we have developed many alternatives to use instead of fire for heating processes. One of such remarkable invention is the principle of “Dielectric heating”. Let’s see how this principle works and how it’s being applied.

What is Dielectric Heating?

The definition of dielectric heating can be stated as – ‘the process of heating up material by causing dielectric motion in its molecules using alternating electric fields“. All materials are made up of molecules that are composed of atoms. The Dielectric Heating circuit diagram is shown below.

Polar molecules contain electric dipole moments. When such molecules are exposed to the electric field, they try to align themselves in the direction of the field. When the applied field oscillates, these molecules of the material undergo rotations in order to keep themselves aligned with the field. When the field changes direction, these molecules also reverse their direction. This process is called “Dielectric Rotation”.

Dielectric Heating
Dielectric Heating

The temperature of the molecules is related to the kinetic energy of the molecules. In the dielectric rotation of the molecules, as the kinetic energy of the molecules increases, the temperature of the molecules increases. When the molecules collide or come in contact with other molecules, this energy gets transferred to all parts of the material thus heating up the material.

Thus dielectric rotation in the material is often referred to as Dielectric heating of the material. This heating is done using either electric fields of RF frequencies or electromagnetic fields. The applied field should be oscillating for dielectric rotation to take place. The frequency and wavelength of the applied field also affect the functioning of the system.

Dielectric Heating Working

As described below, the circuit diagram of the dielectric heating system consists of two metals plates to which the electric field is applied. The material to be heated is placed in between these two metals. There are two types of ways in which material are heating using the heating process.

Heating using low-frequency waves, as a near – field effect and heating with high-frequency waves using electromagnetic waves. The type of materials heated using these different types of waves is also different.

Low-frequency waves have higher wavelengths. Thus they can penetrate through non-conductive materials more deeply than electromagnetic waves. The systems using low-frequency fields should have the distance between the radiator and absorber to be less than 1/2π of the wavelength. So, the process of heating using a low-frequency electric field is near – contact process.

Higher frequency systems have lower wavelengths. Electromagnetic waves and microwaves are used for these systems. In these systems, the distance between metal plates is larger than the wavelength of the applied field. In these systems, conventional far-field electromagnetic waves are formed between the metal plates.

Applications of Dielectric Heating

Dielectric heating principle using high-frequency electric fields was proposed in the 1930s at Bell Telephone Laboratories. By varying the frequency of electric fields the Dielectric systems are designed for many types of applications.

When Microwaves are Used

In this dielectric heating, the 2.45GHz of the microwave of frequency is used. Microwave ovens used in homes are an example of this type of applications. These systems provide less penetrative and highly efficient heating system. Microwave volumetric heating provides a larger penetration depth. Thus this heating is used for heating liquids, suspensions, and solids on an industrial scale.

Microwave Oven
Microwave Oven

Microwave volumetric heating is applied for pasteurization, Flash pasteurization, microwave chemistry, sterilization, food preservation, biofuel production, etc.

When Radio Frequencies are Used

  • RF dielectric often finds applications in the crop production area.
  • This type of heating is used to kill some pests in food after harvest of the crop.
  • This type of heating can heat materials uniformly.
  • This type of heating can process food quickly.
  • Diathermy, the process of RF heating of muscle for muscle therapy uses this type of heating.
  • The process called Hyperthermia therapy, in which higher temperatures are used to
  • kill cancer and tumor tissues, heating with RF frequencies is applied
Shortwave Diathermy
Shortwave Diathermy

Food Processing

In post-baking of biscuits in the production line, RF dielectric heating will reduce the baking time. Right size, shape and color biscuits can be produced with oven but RF heating can remove the remaining moisture from already dried parts of the biscuits.

  • RF heating can increase the capacity of the oven, used in food production factories, up to 50%.
  • Cereal-based baby products and breakfast cereals use the post-baking by RF dielectric heating.
  • In the drying of food, dielectric baking is used along with conventional baking.
  • When an electromagnetic dielectric is used for the baking better quality of food is achieved.
  • Nutritional and sensory properties of food can be preserved during food processing when electromagnetic dielectric heating is used, as higher processing temperatures can be achieved in a shorter amount of time.

Right from the period of its invention, dielectric heating is being used in various forms. From an amazing food processor to a precise Electro surgery method, dielectric had found its application in almost every field of science.

Dielectric heating mechanism setup can be viewed as similar to the structure of the capacitor. In capacitor dielectric is placed in between two conducting plates and electricity is produced in a dielectric. Whereas in a dielectric heating system, the material to be heated is placed in between two conducting plates, to which electric field is applied and heat is generated inside the material.

Now a day’s dielectric heating has found many applications in the agriculture industry, for implementation of many pest control methods. The electric field applied for a microwave oven is Lower frequency or higher frequency field?