Sanyo SM-GA0005 service manual Heating Principle of Microwave

1. THE HEATING PRINCIPLE OF MICROWAVE

Microwave is one kind of radio wave whose wavelength is very short, frequency is very high. Therefore, it is called ultrahigh frequency electromagnetic wave. Microwave can heat food mainly result in the mutual affect of the food in the microwave field and the microwave field itself.

Under the affect of microwave field, the thermal effect mechanism produced from the mutual affect of the microwave and the food includes two aspects. One is Dielectric loss of polar molecule; the other is conductive loss of ion.

Usually, food is constituted of organism (plant and animal). The organism is formed by all kinds of polar water molecule, polar protein molecule, and all sorts of saltion. The center of gravity of the positive and negative charge in the molecule is not coinciding. In normal condition, the molecule is in irregular order due to its thermal action, thus the food do not appear polarity. (FIG.1-la). Under the action of outer electric field, the positive end of the polar molecule trend to the negative electric field, the negative end of polar molecule trend to the positive electric field, and somewhat arrange in order through the direction of the electric field (FIG.1-1c). This phenomenon usually is called “TORQUE POLARITY”. When the outer electric field apply for the opposite polarity, the polar molecule then arrange an opposite direction order accordingly (FIG.1-1b). If the direction of the outer electric field changed repeatedly, the polar molecule would repeatedly sway accordingly. During the swaying, it is understanding that the polar molecule would produce heat due to somewhat similar friction among them. When the electric field is applied for ultrahigh frequent microwave field from the outside, its direction would change tens billion times per second, so do the molecule. This kind of molecule swaying producing similar frictional heat from the interference and block of the action strength among the molecule, and changed to microscopic microwave heating. Microwave heating not only concerned the nature of the matter itself, but also closely connected with the electric strength and frequency. When the frequency is low, the molecule swaying rate and the acute degree of the mutual friction among the molecule is low, and would produce much heat. When the frequency is too high, as the swing of the polar molecule is with rotating inertia, it made the swing do not in line with the changing rhythm of the electric field because of the friction drag, thus, actually lowed the polar molecule swaying speed. The friction dragging degree is concerning about the magnelectric wave frequency, polar molecule shape, and the matter’s sticky degree. To different matter’s molecule, there is different special frequency zone. Those absorbing microwave energy from this zone are most capable to turn microwave energy to heat energy.

(a) (b) (c)

Fig.1-1

Apart from the above said action, there is another action which is electric ion under the action of microwave field, act fiercely accompanied with the acceleration of electric field. The positive ion transfer to the negative polarity of the field while the negative ion does opposite. Accompanying with the changing electric field, the electric ion hanging accordingly. During the transferring, heat produced with the crash among the ion. This kind of action takes the main effect to those microwaves heating of high salt molecule.

No matter it is the polar molecule swaying or the ion transferring, they both are turning the microwave energy which the heating matter got from the microwave field to heat energy. From the analysis of theory, we can draw such a conclusion that the power which a unit of volume matter absorbed from the microwave field as the following formula:

Pa=KE fErtgδ

Pa Stands for the power the heated matter adsorbed from the microwave field.

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