" Meals in a Minute " - The mystery behind the Microwave Oven
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| Microwave Oven |
Microwave oven is one of the most widely used household appliances. Most of homes and most of conveniences store and restaurants have microwave oven. The reason for its popularity is that it cooks food in an amazingly short amount of time. They are also extremely efficient in their use of electricity because a microwave oven heats only the food – nothing else.
OPERATING PRINCIPLE OF MICROWAVE OVEN
A microwave oven uses microwaves to heat food. Microwaves are radio waves.
In the case of microwave ovens, the commonly used radio wave frequency is roughly 2,500 megahertz (2.5 gigahertz).
Radio waves in this frequency range have an interesting property : they are absorbed by water, fats and sugars. When they are absorbed they are converted directly into atomic motion and motion is converted into heat.
Microwaves in this frequency range have another interesting property: they are not absorbed by most plastics, glass or ceramics. And metal reflects microwaves, which is why metals cause spark in a microwave oven. The reason that metal reflects microwaves is that no electronic waves resident in inside of conductor because conductor’s conductivity is infinity as we studied in our course.
Let’s look at this in detail. Molecules of all food are consist of a dipole and have positive charge in one side and have negative charge in another side. If we put electromagnetic fields in this, all molecules are rearranged : +charge is to negative pole pole and –charge is to positive pole. In this process molecules heat is produced by friction. The frequency of microwave oven is 2,500 megahertz as we saw before. Then microwave of this frequency change the direction of electromagnetic fields 2,500,000,000 times in 1 second. Consequently the heat efficiency of a microwave oven is greatly high.
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| Advantages and Disadvantages of Microwave Oven |
Technical Details of of Microwave Oven
A microwave oven consists of:
- A high voltage power source, commonly a simple transformer or an electronic power converter, which passes energy to the
magnetron
- A high voltage capacitor
connected to the magnetron, transformer and via a diode
to the chassis.
- A cavity magnetron, which converts
high-voltage electric energy to microwave radiation
- A magnetron control circuit (usually with a microcontroller)
- A waveguide (to control the direction
of the microwaves)
- A metal cooking chamber
A microwave oven heats food by passing
microwave radiation through it. Microwaves are a form of non-ionizing electromagnetic radiation with a frequency higher than ordinary radio waves but lower than infrared light. Microwave ovens use frequencies in one of the ISM (industrial, scientific, medical) bands, which are reserved for this use, so they don't interfere with other vital radio services. Consumer ovens usually use 2.45 gigahertz (GHz)—a wavelength of 12.2 centimetres (4.80 in)—while large industrial/commercial ovens often use 915 megahertz (MHz)—32.8 centimetres (12.9 in). Water, fat, and other substances in the food absorb energy from the microwaves in a process called dielectric heating.
Many molecules (such as those of water) are electric dipoles, meaning
that they have a partial positive charge at one end and a partial
negative charge at the other, and therefore rotate as they try to align
themselves with the alternating electric field of the microwaves.
Rotating molecules hit other molecules and put them into motion, thus
dispersing energy. This energy, when dispersed as molecular vibration in
solids and liquids (i.e., as both potential energy and kinetic energy of atoms), is heat.
ANEESH P THANKACHAN
M. E (Communication Systems)
B. Tech (Electronics & Communication Engineering)
Engg. Diploma (Applied Electronics)
Associate
Professor , Department of ECE
Younus College of Engineering & Technology, Kollam
