The principle of operation of a microwave oven: circuits, frequency and video


How exact­ly does a microwave oven work? What caus­es food, water and oth­er sub­stances to heat up, while air or glass in a microwave oven almost does not heat up? How to prop­er­ly han­dle the microwave so as not to spoil it and the dish being pre­pared? You will find the answers to these ques­tions in our arti­cle!

The principle of operation of the microwave

The cor­rect full name of the microwave oven is an oven with microwave cur­rents. Inside it (behind the dash­board) there is a spe­cial device for emit­ting radio waves — a mag­netron, which can be seen from the dia­gram:

Microwave oven design

When the mag­netron is oper­at­ing, the elec­tro­mag­net­ic oscil­la­tions of a cer­tain fre­quen­cy emit­ted by it cause the dipole mol­e­cules inside the fur­nace to oscil­late at the same fre­quen­cy. The most com­mon dipole mol­e­cule in nature is the water mol­e­cule (in foods there are also fats and sug­ars). At the mol­e­c­u­lar lev­el, a high vibra­tional fre­quen­cy trans­lates into a rise in tem­per­a­ture, so any food with a high water con­tent heats up quick­ly. If there are very few or no water mol­e­cules inside the prod­ucts (or mate­ri­als), heat­ing almost does not occur.

The depth of pen­e­tra­tion of microwaves is small — 2–3 cen­time­ters, how­ev­er, the sur­face of the cooked dish is eas­i­ly pierced by microwaves, and in depth they meet the resis­tance of water mol­e­cules, so the prod­uct actu­al­ly warms up from the inside.

Any con­duc­tive mate­ri­als inside the microwave will get hot. Dif­fer­ent abil­i­ty to con­duct cur­rent in our case means a dif­fer­ent heat­ing rate.

In order for the heat­ing of prod­ucts to occur even­ly, sev­er­al approach­es are used:

  • Heat-resis­tant glass disc at the bot­tom of the microwave oven. It rotates togeth­er with the dish, expos­ing all its sides to the radi­a­tion of the mag­netron.
  • Microwave. They are fed through a spe­cial wave­guide (wide tube) from the mag­netron to a rotat­ing reflec­tor, usu­al­ly locat­ed in the upper part of the microwave oven. In such microwave ovens, it is pos­si­ble to heat motion­less dish­es of large size and weight.

Types of microwaves

There are also so-called invert­er microwave ovens. They dif­fer from con­ven­tion­al mod­els in that the mag­netron oper­ates con­tin­u­ous­ly, but with reduced pow­er con­sump­tion. This is achieved by using a so-called invert­er (DC-to-AC con­vert­er) in the fur­nace instead of a tra­di­tion­al trans­former.

Vit­a­mins are bet­ter pre­served in invert­er ovens, and the sur­face struc­ture of the dish is less destroyed, but there is no fun­da­men­tal dif­fer­ence.

In many mod­els of microwave ovens, the mag­netron is cov­ered with a spe­cial translu­cent plate. It is trans­par­ent to microwave rays, but does not allow steam, splash­es of grease and oth­er for­eign mat­ter to enter the microwave oven through a hole in the shield­ing. Do not remove this plate, and if it is required for clean­ing from fat, then after com­plete dry­ing, be sure to return it to its place.

Look for every­thing about clean­ing a microwave oven in this arti­cle:

Despite pop­u­lar belief, microwave radi­a­tion does not kill germs. At least not sci­en­tif­i­cal­ly proven. On the oth­er hand, the com­plex effect of high tem­per­a­ture and microwaves on water mol­e­cules inside bac­te­ria and virus­es with­in a few min­utes reduces their num­ber many times over, and your immune sys­tem copes with those that remain.

Microwave operating frequency

Most mag­netrons emit waves at a fre­quen­cy of 2450 MHz (mega­hertz, or mil­lions of oscil­la­tions per sec­ond). These are waves of decime­ter length (12.25 cm long). Some indus­tri­al instal­la­tions, for exam­ple in the USA, oper­ate at 915 MHz. Forced oscil­la­tions of water mol­e­cules are not res­o­nant oscil­la­tions, since for them the res­o­nant fre­quen­cy is an order of mag­ni­tude high­er — 22.24 GHz (GHz, or bil­lions of oscil­la­tions per sec­ond).

There is no need to be afraid of harm­ful radi­a­tion from the microwave. The first mass pro­duc­tion of microwaves was made in Japan by Sharp in 1962. Many years have passed since then, tens of mil­lions of Japan­ese peo­ple have been heat­ing food in microwave ovens for decades, and the aver­age life expectan­cy of the Japan­ese is the envy of the whole world.

At a dis­tance of half a meter from the microwave oven, the effect of microwaves weak­ens 100 times, so if you are afraid of get­ting radi­a­tion, it is enough to stay away from the microwave at arm’s length.

You can find more infor­ma­tion about the effects of microwave ovens on humans here. Only sci­en­tif­ic facts!

How does a microwave grill work?

The grill allows you to grill food in the microwave using reg­u­lar heat instead of microwaves. It is she who makes an appe­tiz­ing crust on dish­es, which does not appear dur­ing con­ven­tion­al microwave pro­cess­ing.

The grill spi­ral is locat­ed at the top of the oven and there are two types:

  • heat­ing ele­ments (ther­mal elec­tric heaters). A heat­ing ele­ment is a met­al tube, inside of which there is a thin spi­ral made of an alloy of nick­el and chromi­um. A cur­rent pass­es through the coil, and it heats up.
  • Quartz. A quartz grill is also a heat­ing ele­ment, only instead of a met­al tube there is a glass shell, between the spi­ral and the tube there is insu­lat­ing quartz sand.

Ordi­nary met­al heat­ing ele­ments can often be adjust­ed — moved to the back wall or low­ered, but the glass sur­face of a quartz grill is eas­i­er to clean (grease and car­bon deposits do not eat into glass like they do into met­al).

There are designs of microwave ovens with grill and con­vec­tion. Con­vec­tion is sim­ply blow­ing hot air around your food while cook­ing. For such blow­ing, a fan is installed in the microwave, blow­ing heat­ed air from the grill spi­ral towards the dish.

Most mod­els of microwaves allow you to use both the heat­ing ele­ment and the microwave at the same time. How­ev­er, keep in mind that this com­bi­na­tion can get the out­let and wires in your room very hot.

Grill in the microwave

Read the fol­low­ing arti­cle about the prin­ci­ples of choos­ing a microwave oven for your needs:

Microwave Instructions

To prop­er­ly han­dle your microwave, you need to care­ful­ly approach all points — from the choice of dish­es to the cor­rect shut­down after use.

What utensils to use?

The best mate­r­i­al for heat­ing in the microwave is heat-resis­tant glass­ware. Porce­lain and oth­er ceram­ic prod­ucts, paper (card­board) are also well suit­ed. Microwaves pass through them very eas­i­ly and almost do not heat them. But dish­es from the fol­low­ing mate­ri­als must be dis­card­ed:

  • Plas­tic. It trans­mits microwave radi­a­tion well, but due to tox­ic com­po­nents dur­ing man­u­fac­ture (for exam­ple, poly­styrene foam), it can be haz­ardous to your health.
  • Met­al. They con­duct elec­tric­i­ty with­out pass­ing microwaves. So cook­ing or sim­ply reheat­ing a dish in an alu­minum pan or cast iron pot will not work. The met­al sim­ply will not let elec­tro­mag­net­ic waves through to the prod­ucts, and they will remain cold. In this case, the met­al itself, of course, heats up, and prod­ucts can also heat up from its heat. But this can lead to a break­down of the microwave oven, and it will take a long time to cook the dish. Click here for microwave oven repair instruc­tions.

Some mate­ri­als may con­tain met­als, and this can be dif­fi­cult to guess in advance. For exam­ple, it is crys­tal. So you should care­ful­ly read on the label what mate­ri­als were used in the pro­duc­tion of a par­tic­u­lar dish.

  • Melamine. This is a light and beau­ti­ful mate­r­i­al for dish­es, sim­i­lar to porce­lain, but it can­not be placed in a microwave oven. The fact is that when heat­ed, it releas­es tox­ins that are dan­ger­ous to your health.

As for the shape of the dish, it can be any, but not with a nar­row neck, since when used for heat­ing in the microwave, it can be dan­ger­ous. The fact is that some liq­uids are heat­ed to the boil­ing point, but there is no vig­or­ous mix­ing inside the vol­ume. But when you take out such a jug or flask from a microwave oven, the liq­uid will instant­ly boil, boil­ing foam will pour out of the con­tain­er, and you can get burned. For exam­ple, dis­tilled water and some refined veg­etable oils behave in this way under cer­tain con­di­tions.

We rec­om­mend that you read the arti­cle about which dish­es are suit­able for the microwave.

Proper handling of products

Ini­tial­ly, it is worth deter­min­ing exact­ly what can­not be defrost­ed in the microwave:

  • But­ter. If you put it in the microwave and leave it for a long time, it will not only melt, but also boil, stain­ing the entire oven from the inside. This hap­pens because inside the oil there is not only oil itself, but also water. It boils at 100 degrees, and oil at about 120. So water can turn into steam before the oil melts, and the water vapor will spread the oil all over the stove.

Approx­i­mate­ly the same thing can hap­pen with oth­er prod­ucts that some­times need to be melt­ed, for exam­ple, with choco­late, so it is bet­ter to do this not in the microwave, but in a cou­ple.

  • Hard shell prod­ucts. For exam­ple, these are eggs, toma­toes, whole bird liv­er. When heat­ed, some of the water does not just grad­u­al­ly heat up, but imme­di­ate­ly turns into steam. If you heat food for a long time, then even more steam is formed from direct heat­ing. This steam has nowhere to go, so the pres­sure inside the con­tain­er increas­es and leads to an explo­sion.
  • Her­met­i­cal­ly sealed con­tain­er. For exam­ple, canned food and bot­tles. The rea­son is the same as in the pre­vi­ous para­graphs — the prob­a­bil­i­ty of an explo­sion is high.

Microwave use

Fur­ther, it is worth tak­ing into account tips on how to prop­er­ly han­dle food when heat­ing or cook­ing in the microwave:

  • Sausages tight­ly packed in a cas­ing must be pierced with a fork before microwave heat­ing to cre­ate holes for steam to escape, oth­er­wise it will turn the sausages from the inside.
  • In eggs and oth­er prod­ucts, you need to destroy all the out­er and inner shells, for exam­ple, make an omelet or cut the liv­er.
  • For cook­ing eggs and oth­er prod­ucts in the microwave, spe­cial saucepans with shield­ing are used. Water is poured into it, it is it that is heat­ed by microwave waves, and elec­tro­mag­net­ic radi­a­tion does not reach the eggs — they are cov­ered by a screen.
  • If a small dish is placed in the microwave, you should add a reg­u­lar glass of water to it. So you will avoid over­heat­ing of the mag­netron.
  • It is bet­ter to salt any liq­uid dish­es in the microwave in advance, and not after cook­ing. This way you save time and ener­gy. The fact is that dis­tilled (unsalt­ed) water in the microwave heats up and boils, but longer than ordi­nary water.
  • A very heav­i­ly frozen prod­uct (meat, for exam­ple) will be defrost­ed in the microwave for quite a long time, and you need to turn on the microwave oven at the min­i­mum pow­er. The rea­son is that ice mol­e­cules are not water mol­e­cules, microwaves do not shake them as intense­ly. In addi­tion, ice mol­e­cules form a fair­ly rigid struc­ture and are not as easy to “rock” as water mol­e­cules.

Dry bread is often rec­om­mend­ed to be “soft­ened” in the microwave, but it can ignite with pro­longed expo­sure and max­i­mum microwave pow­er. The same can hap­pen even with microwave-safe pop­corn. There­fore, when such foods are placed in the microwave oven, one must be vig­i­lant.

On/off rules

You can not turn on an emp­ty microwave, espe­cial­ly at full pow­er:

  1. Inside the oven, all walls (and even the door) are a spe­cial met­al­lized screen that reflects microwaves back into the microwave. The only place where there is no screen is the hole for the exit of elec­tro­mag­net­ic waves from the mag­netron.
  2. When food is on the tray, the microwaves use their ener­gy to heat the food. If there is noth­ing to absorb the ener­gy, microwave radi­a­tion is reflect­ed from the walls of the shield­ing sur­faces, while the wave den­si­ty increas­es more and more.
  3. Microwave radi­a­tion gets back into the mag­netron, and if it con­sists of met­al, it will sim­ply over­heat and may fail.

It is believed that after heat­ing a dish in a microwave oven, it is bet­ter to let it stand for 3–5 min­utes. Then the so-called “free rad­i­cals”, that is, parts of mol­e­cules that have bro­ken apart under the influ­ence of microwaves, have time to neu­tral­ize.

Video: How does a microwave work?

All of the above about the prin­ci­ple of oper­a­tion of the device is well illus­trat­ed in the fol­low­ing video:

After read­ing our arti­cle, you have become much bet­ter at under­stand­ing the prin­ci­ple of oper­a­tion of a microwave oven. Now you know what it can do bet­ter than a con­ven­tion­al oven and elec­tric stove, and what it can­not, and what actions are gen­er­al­ly unac­cept­able when work­ing with a microwave.





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