Fundamentals Of Microwave Heating

Microwaves are electromagnetic (EM) waves of very short wavelength. In the EM spectrum, microwaves lie between the television frequencies and infrared. In terms of wavelength, radio waves are measured in kilometers, television frequencies in meters, microwaves in centimeters, and infrared in microns. The wavelength and frequency are related by the expression:

wavelength (A0)

speed of light (c) frequency if)

Thus for a typical microwave oven frequency of 2,450 MHz, the wavelength (/0) is

Microwaves, as with other wave energy, radiate from a source in all directions. These waves carry energy and the amount of energy they carry depends on the amount of energy imparted to them. The energy of microwaves comes from electrical energy that is converted by a power supply to high voltages that in turn are applied to the microwave power tube or generator. The most common power tube used in microwave ovens is the magnetron and it broadcasts its energy into the applicator, which may be an oven, a waveguide, or some other device containing the material to be heated.

Microwaves, like infrared and visible light, are reflected, transmitted, and absorbed. They are reflected from metal surfaces: the microwave oven is basically a metal box in which the waves reflect from the walls and create a resonant system. Microwaves are transmitted, that is, they pass through many materials including glass, ceramics, plastics and paper. Some materials are only partially transparent to microwaves; that is, they absorb some energy. When microwaves are absorbed their energy is converted to heat.

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