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Microwave oven was developed in US at 1946.
There was phenomenon it became warm when hands approached to the wave during experiment of radar, and this is the initial idea of Microwave oven. While oven bakes the food by elevating inner temperature, Microwave oven does it by using moisture contained in food.
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Water molecule, structuring the most part of
food, has polarity. Accordingly, the side of
hydrogen ion shows relatively positive charge
and the side of oxygen ion negative, respecti-
vely.
If molecule has polarity like this, the one side
can bind to the opposite charged part of the
other molecule. In this time, when microwave is transmitted to this bound molecules, the electrical vector of microwave is
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vibrated to make bound molecules rotate. In here, if the rotation is inhibited by other molecule, this bond will be broken. Microwave energy is entered into the molecule in this moment.
After a wile, energy is emitted by re-binding molecules, and this energy make cook the food as an internal energy
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Microwave is transmitted to food in
various directions. This can be
shown in the structure of Microwave
oven. Microwave is reflected in vari-
ous direction by the rotational plate
of Microwave oven.
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In general, it is said the principle of microwave oven is that the resonance is occurred from the same oscillation frequency of microwave and water molecule. However, the oscillation frequency of microwave is 2.45GHz, and significantly different from that of water, 9GHz in T =0กษ. Then, if we adopt the microwave with the same resonance frequency of water molecule, it make faster absorption of energy, but why we do not use it? The solution for this may be explained with electromagnetic. The frequency of microwave is related to the penetration depth of it. Penetration depth means the depth that microwave can penetrate through the surface of food. The more frequency the lesser penetration depth rapidly. Therefore if the frequency of microwave is raised up to the frequency of water, it may cook faster but we cannot eat the surface of it.
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Most of current commercial microwave ovens are manufacture by attaching the heat transfer equipment of oven or grill to microwave heating device. Microwave oven composed of heating source which emitting microwave, power source, control panel, cooling fan, and case. And it is also equipped the turn table for rotating foods for uniform distribution of microwave. Heating source is composed of special electrode vacuum tube of Magnetron. This is a device to generate the ultra high frequency (UHF), which concentrates on food through output antenna. Strong frequency emitted from microwave oven is harmful to human body, so it must not be leaked. For this reason, it is manufactured with safety device not for opening door during operation and also with metallic case.
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