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How does RF heat food?



For RF heating, food products are placed between two electrodes which generate an alternating electrical field. Two major mechanisms are responsible for the interaction between food and the electrical field. One of them is the dipole rotation of polar molecules, and the other is ionic conduction caused by charged ion movement.
Polar molecules in food such as water have an electrical dipole moment, and the positive charge center and negative charge center in these polar molecules do not coincide. When subjected to an electrical field, polar molecules will rotate to align themselves to the field. As a result, the negative and positive charges move to different ends and lead to polarization. This phenomenon is known as dipole rotation (Marra et al., 2009). If placed in an alternating electrical field, the polar molecules will rotate in an opposite direction and back again to follow the changing fields. During this process, the friction among surrounding molecules converts the electromagnetic energy to heat and gives rise to an increasing temperature of the treated materials.
In addition, dissociated ions in foods also move accordingly with the applied alternating electrical field. The direction of motion of the molecules varies with time due to the changing electrical fields. Heat will also be generated within the material by the friction among molecules caused by the forward and backward oscillation of the ions  in the material (Buffler, 1993). This mechanism is called ionic conduction. Ionic conduction is the dominant mechanism for RF heating (Ryynänen, 1995).