An indispensable assistant in the kitchen is the microwave. The operating principle of a microwave oven and types of models

Microwave ovens have been part of our everyday life for a long time, but debates about their usefulness and safety are still ongoing. It is curious that, solving such issues on various forums and in personal meetings, the vast majority do not even approximately imagine the principle of operation of a microwave.

That is why, before asking yourself whether it is your friend or foe, it makes sense to find out what this amazing unit is, capable of boiling a glass of water or cooking a chicken without using a visible heat source. Almost everyone has seen a microwave in operation, but few people imagine how it does it.

Action and principle of operation

The principle of operation of a microwave oven is implied in its name - the effect on the body (in in this case products) - microwave radiation (microwave radiation or simply microwave). Under the influence of high frequency electromagnetic vibrations food is heated to high temperature, which allows you to heat up or even cook dishes without using classic thermal heaters. By the way, this same method is used not only for preparing food products, but also for heat treatment of technical products: annealing and hardening, say, drills, gears, knives, etc.

The main condition necessary for a microwave oven to operate is the presence of so-called polar molecules in the object. It is they who are affected by the electromagnetic field of the device. Fortunately, almost all food products (with the possible exception of completely dehydrated ones) contain water, which consists of such molecules. Once in a powerful alternating electromagnetic field, such molecules begin to quickly change their position, following the constantly changing direction magnetic field. During the process of rotation, these molecules literally rub against each other, and everyone knows what happens. Try quickly rubbing your palms against each other - do you feel the warmth?

Thanks to the alternating electromagnetic field, polar water molecules begin to rotate rapidly.

The main difference between the effect of microwave radiation on an object and ordinary friction or heating with an open flame is that not only the surface of the object is heated, but also its deep layers. This is due to the fact that microwave radiation acts not only on the surface of an object, but also penetrates deep into it, causing molecules to move and heat up.

The penetration depth depends on the radiation frequency. And for standard microwave ovens operating at a frequency of 2.4 GHz, it is 1.5–2.5 cm. It is not difficult to guess that, for example, a pie placed in a microwave oven will warm up completely and evenly both inside and outside. Moreover, he will do this in the shortest possible time, since the rate of heating of the body in the microwave field is 0.3-0.5 degrees per second. 10 seconds - +5 degrees. Minute - +30 degrees.

Advantages and disadvantages

So, it’s time to formulate the main differences between microwave heating and classical heating:

The only seemingly drawback inherent in microwave ovens is the impossibility of frying, but the designers solved this issue by equipping the device with conventional thermal electric heaters, like an electric oven. With their help you can easily fry the product. In addition, there are so-called Crusty plates, made of a special material that is safely heated by microwave currents. Place a chop on such a plate and the stove will not only cook it quickly, but also fry it, since this pan heats up to 200 degrees.

Microwave oven device

Now it's time to figure out how a microwave works. The heart of any such stove is a special generator that creates a high-frequency electromagnetic field of high intensity. It's called a magnetron. Next, the field created by it is directed to the product chamber using specially designed waveguides. He does this in such a way that the entire internal volume of the chamber is “filled” with the field evenly, ensuring high-quality heating of products of any volume. Additionally, this is facilitated by the rotating tray that most microwave ovens are equipped with.

The magnetron occupies the most honorable place under the lid of the device.

The operation of the RF generator is controlled by an electronic unit assembled on a microprocessor. The microprograms built into the unit allow you to set the desired cooking mode, control the temperature in the chamber, humidity, and cooking time. They also monitor the safety of using the stove - whether the protective door is closed, whether there is an insulation breakdown, whether the temperature inside the chamber has risen above critical, etc. The controller is controlled from one type of remote control or another - push-button, touch, etc. And, of course, , the furnace also has a power supply that supplies energy to all the electronics and the magnetron itself.

Danger and harm of microwave ovens

And now the most main question, which worries almost every microwave owner: does the device pose any danger to others? There are many myths about the dangers of using microwaves. technologies in everyday life. The main ones:

Radiation hazard.
Electromagnetic radiation hazard.
Poor influence of microwaves on the quality of prepared products.
Possibility of physical damage by a microwave field.
Increased risk of injury electric shock high voltage.

Radiation damage

According to this myth, everyone who is near a microwave oven receives radiation exposure. Moreover, even when the stove is turned off, it “radiates” no worse than a Chernobyl tractor. But if you believe the basics of nuclear physics (everyone took it in school), the radiation that everyone is so afraid of and that really poses a danger is ionizing radiation.

Take a look at the list, which lists the types of electromagnetic radiation, arranged in descending order of their wavelength:

radio waves - 10 km - 0.1 mm;
infrared radiation - 1 mm - 780 nm;
visible radiation (light) - 780 - 380 nm;
ultraviolet radiation- 380 - 10 nm;
x-ray radiation- 10 - 5 pm;
hard (gamma) radiation - less than 5 pm.

Of the entire list, only the last two items are fully ionizing and partially ionizing - the third from the bottom (UV light). And only gamma radiation can leave behind induced radiation. Wavelength electromagnetic field microwave oven- 12 cm. It is much more logical to be afraid of the visible light emitted by the Ilyich light bulb, the ionizing ability of which is 3 orders of magnitude higher than microwave radiation. But, despite the obvious, no one is afraid of light bulbs, almost everyone is afraid of microwave ovens.

Does high-frequency radiation change the properties of products.

There is an opinion that, after being in the microwave, products change their physical structure. Some connections are supposedly destroyed, others appear, the charge, pole, degree, memory changes - whatever. After all this disgrace, healthy foods turn into poison.

Microwave radiation, as mentioned above, affects polar molecules, which are water molecules. Today, science knows for certain that water is an amorphous body and has no structure at all unless it is in a frozen state. How can this very structure change if the amorphous body does not have it at all?

The birth of such a myth is most likely associated with the concept of “structured water”, which appeared thanks to all sorts of pseudosciences such as homeopathy and “businessmen” selling “charging” water trays and other technological wonders of parallel worlds.

Electric shock

How electrically safe is the device?.

The fear that a microwave oven is dangerous in terms of electric shock is, in principle, understandable. To operate the magnetron, a high voltage source is required - about 4 kV. If we add to this the power of a modern microwave, which can reach a kilowatt, then all the horror of a person who is far from electricians becomes understandable. Nevertheless, this same person quite calmly uses a one and a half kilowatt vacuum cleaner and a two kilowatt electric stove.

Remember the usual CRT TV, which has served us for decades and continues to serve us to this day. Accelerating anode voltage its kinescope reaches 30 kV. This is almost an order of magnitude higher than the voltage on the magnetron. If you open the microwave, you can get energized. But also on TV back cover with just four screws! Now think about it: how many of your friends have been electrocuted by an evil TV? Thus, in terms of electrical safety, a microwave oven is no different from any other household appliance.

Is microwave radiation harmful to the body?.

Yes, microwaves are harmful to humans. But a lot of modern devices operate at the same frequency: Wi-Fi modem, cell phone, smartphone. Working with them is considered safe. Is microwave radiation harmful or harmless? Harmful, but only when exceeding a certain level. Your mobile phone emits radiation, but its transmitter power is low. Even though you hold it close to your temple, periodic conversations on the phone will not cause any particular harm to your health. Another thing is the microwave oven. The power of its “transmitter” reaches thousands of watts.

But, firstly, unlike a mobile phone, the magnetron radiation is not directed in all directions, but in working chamber. Secondly, and this is the main thing, the camera, like its door, has special coating, preventing radiation from escaping beyond work area. Of course, the coating does not block microwaves 100%, but this is not necessary. You don’t hold the microwave to your temple like a telephone, and you don’t use it with your nose buried in the door for hours. In addition, the microwave intensity decreases in proportion to the square of the distance.

What do the numbers say about this? Opening medical documents, standardizing the maximum permissible microwave radiation safe for humans and we read: no more than 10 μW/cm2. Is it a lot or a little? It's time to look at the picture below:

Near the microwave oven door itself, the electromagnetic field strength is quite high - 5 mW/cm2. But already at a distance of half a meter it weakens by two orders of magnitude, and at a distance of one and a half meters it is twice as low as the maximum permissible level. Thus, if you don’t literally hug the microwave on and don’t use it around the clock, then you don’t have to worry about your health. But can the door be opened? It is possible, but the magnetron will immediately turn off, since it has foolproof protection. The same protection will not allow you to put your hand in(and for some, even the head) into a working device in order to check its serviceability “by touch”.

As soon as you open the door, the automation will remove power from the magnetron.

Thus, a working microwave oven, subject to elementary rules operation, described in detail in the attached instructions, is absolutely safe for humans.

The microwave oven is currently very popular and is the most popular kitchen appliance. Using a microwave oven, you can not only heat or cook food, but also defrost food and even disinfect some kitchen utensils that do not contain metal. This device has become completely commonplace today.

Microwave oven is a household electrical appliance, which is intended mainly for cooking or heating food in fast mode. Microwaves are also used in some industries where necessary materials need to be heated.

Unlike conventional ovens, heating of various products in this device occurs quite quickly, since radio waves are able to penetrate deep inside the products. This radically reduces the heating of any product and helps preserve all the nutrients in it.

The design of all microwave ovens consists, as a rule, of the same components. The design of microwave ovens has main and auxiliary elements. Appearance These devices can be very diverse. Sizes, colors and functions may vary for each individual oven, they may be different.

Structure of a microwave oven:

A chamber equipped with a rotating stage;
The magnetron is the main element - a microwave emitter;
Transformer;
Metal case with a door that is locked when the device is operating;
Management and communications scheme;
Waveguide.

The microwave must also be equipped with a fan inside. Its purpose is very great, since without it the device itself will not work. This device ensures excellent operation of the magnetron and cools the electronic circuits.

How a microwave oven works: its types

The operation of a microwave oven is very simple, it is based on microwave radiation. The heart of every microwave oven is an element called a magnetron. It is the source of radiation. The frequency of microwaves is approximately 2450 MHz, and the power of modern microwave ovens can be 700 - 1000 W. This stove runs on electricity.

To ensure that the magnetron works well and does not overheat, a fan is installed next to it. It also circulates air inside the oven itself and promotes uniform heating of food or products.

Microwaves enter the oven through a waveguide, and then the walls, which are made of metal, reflect the magnetic radiation itself. Radiation, penetrating deep into products, causes their molecules to move very quickly. These actions promote friction, as a result of which heat is released (physics is present). This is warm and will warm up the food.

Types of electrical appliances:

With grill;
Convection oven;
Inverter controlled device;
A device with microwaves that are distributed evenly;
Mini microwave.

The main advantage of all microwave ovens is their design. The market provides a huge selection of devices; you can choose both a stylish and an ergonomic model. The description of these models will allow you to choose the model you like, which will become not just a decoration for the kitchen, but also its highlight. An example would be a Samsung microwave oven.

Control unit: microwave operating principle

Every microwave has quite a few of these. important element, like a control unit. It, in turn, performs two main functions: maintains the specified power and turns off the device when set time expired. Today, technology has developed a new type of this element - electronic.

Today, an electronic unit can support not only its basic functions, but also some additional ones. Some of them are necessary, while others are not needed at all. Many modern models have a grill, which is also controlled by a control unit.

Today, the command block is equipped with various microprocessors, which, in turn, support the functionality of other programs. Therefore, the power supply can be responsible for the operation of additional functions.

Additional service functions:

Built-in clock;
Power indicator;
Automatic defrost;
An audible signal that indicates a completed operation.

The electronic unit is closely connected with the indicator panel and keyboard. The most important detail such a block is a relay block. It is responsible for the operation of the fan, convector, built-in lamp and even magnetron.

Microwave frequency: magnetron and its components

The principle of operation of a microwave oven is that when the microwave oven is turned on, the magnetron begins to release energy, and then it is converted into heat. This heat is used to heat food. Magnetron is translated as an electric vacuum diode, which consists of a copper anode. This is the most expensive part of the stove.

Heating of food that is inside the microwave occurs under the influence of electromagnetic radiation, that is, radio waves above high frequency. Due to the fact that radio waves penetrate deeply into the heated product, it is heated very quickly and efficiently.

Decoding a magnetron is a device that produces huge amount heat due to the frequency of radiation. The radiation frequency is 2.4 GHz. Coefficient useful action The efficiency of the magnetron is 80%, and the power consumption of this type of furnace during radiation can be 1100 W.

The magnetron device consists of the following parts:

The cylindrical anode is its base, consisting of 10 sectors, each of them made of copper;
In the center is a cathode with an incandescent filament;
The end parts are occupied by magnets, they create the magnetic field necessary for radiation;
A wire loop connected to the antenna, which emits energy.

With the help of an emitter antenna, the energy first enters the waveguide and then into the furnace chamber. The voltage supplied to the anode is 4 thousand W, the filament is 3 thousand W. The magnetron housing is located in a plastic radiator, where a built-in fan blows air over it, and a special fuse is responsible for its overheating.

Design and principle of operation of a microwave oven (video)

WITH English language This statement Microwave oven can be deciphered as a microwave oven. This design is household appliance, which runs on electricity and is distinguished by the fact that it defrosts or heats food very quickly. This happens due to microwave radiation.

The operating principle of a microwave oven is based on the process of converting an electromagnetic microwave field. The electromagnetic field is converted into heat and heats the product placed in the chamber in a non-contact manner. This is the main difference between a microwave and other devices - electric ovens, gas ovens, etc.

In microwave ovens, heating occurs directly within the product being heated, which is why the process takes just a few minutes. And in traditional stoves, heat is directed to the surface of the object, and spreads further depending on the thermal conductivity properties of the product. Of course, this method is less effective than microwave waves, and also requires much more knowledge in the field of cooking.

Even with the passage of time and the development of technology, the structure of a microwave oven remains unchanged. Yes, the design improved and became more comfortable, functionality developed, and new ways of adjusting time and power appeared. But the principle of operation has not changed to this day.

Many people confuse concepts such as “microwave oven” and “microwave oven,” but these are just different names for the same device.

Just ten years ago, microwaves were considered an unaffordable luxury and a simple addition to the kitchen interior. The reason for this was the high cost of such devices, and not everyone could afford such an innovation. But over time, it became clear that this is not a luxury, but a necessity, especially in times of urbanization and the constant race for money.

What causes heating?

The operating principle of a microwave oven is based on an element called a magnetron. This concept is widely known to anyone familiar with the world of radar devices. It was thanks to the magnetron that humanity received the most effective and easy-to-use device for cooking and heating food. This is one of the most bright examples how the developments of heavy industry began to be applied in everyday life with stunning success.

The structure of a microwave oven can be briefly described in these words: a magnetron generates microwave energy, which is converted into heat. The power sources for these elements are special anode-filament transformers-stabilizers, which are the reason for this high price for microwaves. These stabilizers are the most expensive and important element of the furnace.

While studying the operating principle of a microwave oven, we will pay special attention to the design of the magnetic circuit equipped with magnetic shunts. This device makes it possible to change increased voltage only within two percent, in conditions of network voltage fluctuations of 10%. The magnetic core and the significant inductive dissipation force of the high-voltage winding are the main attractions of the microwave oven transformer. In words, everything seems quite complicated, but in reality such a device has proven to be simple and extremely effective.

But at the first stages of development, the creators were faced with such a problem as increased noise when the stove was operating. Excessive noise has always been a problem for many designs household appliances, but manufacturers easily avoided this pitfall. To reduce the noise level, some parts of the magnetic circuit are connected by welding.

The standard microwave body is a rectangular chamber, which plays a significant role in heating. The generated waves are not simply directed towards the heated object - they are reflected from the walls of the housing.

An additional element that makes it possible to ensure high-quality and uniform heating is a rotating saucer in the chamber. By rotating, it allows the waves to evenly impact the surface. The principle of operation is such that the generated waves are by no means uniform - they can be with beams, nodes, etc. The magnetron transmits power to the emitter through a rectangular waveguide.

The door is an important element of the microwave oven

In the production of microwave ovens greatest attention is given to the door. Everyone knows that in every microwave oven the door plays the role of a kind of fuse - as soon as it opens, the operation of the oven stops. The door structure is quite complex, as it is directly related to the level of safety during operation. The operating principle of the door is as follows:

Required perfect shape doors and housings so that the gap is minimal. The door protects environment from the action of microwave radiation, and therefore its creation must be treated with the utmost responsibility.
The perimeter of the door is equipped with a high-frequency choke valve, which is responsible for reducing microwave radiation to the required levels.
The production process uses a special type of plastic that helps absorb radiation.

The control panel is nothing complicated. Usually these are two knobs that regulate the power and cooking time. The timer can be either mechanical or in the form of an electronic dial.

These days many modern models equipped with selectable panels different modes, but in fact these are just minor additions - the basic principle of operation does not change.

Over the years of microwave ovens' existence, much has been said about their detrimental effects on health. In fact, microwave ovens do not emit radioactive radiation, and even allow you to cook healthier food, preserving up to 75% of vitamins in food (which cannot be said about traditional cooking methods). If you follow safety precautions, there will be no harm to your health from the microwave.

If the question comes to your mind about how a microwave oven works, then it will not be difficult to answer it, because this device has been on the household appliances market for quite a long time and its characteristics have been studied far and wide. The operating principle of a microwave oven is based on the effect of microwaves on the product placed inside the device. What a microwave oven and a microwave are will be discussed in detail below.

The operation of devices of this type is based on the transformation of so-called electromagnetic microwave fields. A similar field is converted into thermal energy and heats the food in the chamber. The operating principle of a microwave oven differs from other devices for cooking: ovens (both gas and electric, where heating occurs due to the elementary heating of the contact surface and the surrounding space in the chamber) and stoves.

The operating principle of a microwave allows you to heat only the object itself placed inside. Therefore, the process of heating food occurs quite quickly. At one time, it was this advantage that allowed the microwave to gain popularity and confidently take a leading position in the kitchen appliances market. To defrost or reheat a cooked dish, it was no longer necessary to expend extra energy (to heat the entire chamber). In a few minutes, the electric wave action increased the temperature to the required level. For example, a piece of frozen meat was ready for cutting and further cooking without a long wait.

Traditional types of thermal effects act somewhat differently. Heat is supplied to the surface heated object, as a result of which quite often one can observe such a picture when the outer side of the defrosted dish is already covered with a crust and has begun to burn, but the inside remains frozen. This happens because heating occurs unevenly, the heat is distributed vertically: from the top layer to the inner. This method is much less effective than using a microwave oven; moreover, it requires the owner to have certain dexterity and culinary skills, whereas to prepare a dish in a microwave oven it is enough just press a couple of buttons and expect results.

The electrical circuit of a microwave oven has remained unchanged since the device was launched into mass production. To meet current requirements, the appearance has changed, the devices have become more aesthetically attractive. Many hardware functions have been added, more comfortable methods of control, regulation of the impact power, but the principle itself remains the same as 50 years ago. This is connected not only with the well-known saying “why change something that already works well”, it’s just that the principle itself does not imply any radical changes.

By the way, when it comes to a microwave oven and a microwave oven, you should remember that these concepts are identical, these devices are not different types devices, as some might think at first glance.

A couple of decades ago, a microwave oven was an element of luxury and was more likely to be present in the kitchen as a decorative element rather than as an item for cooking. everyday use. Of course, over time, production technologies became more accessible to the mass market, which led to the widespread availability of microwaves and their ubiquity. Thus, from a luxury item and a rare technological curiosity, the microwave oven turned into irreplaceable assistant in the kitchen, capable of preparing simple dishes in a matter of moments.

A few words about heating

The microwave oven device includes the so-called. This definition should be familiar to anyone who knows how radar works and works.

Microwave like mechanical device, is able to quickly heat food precisely thanks to the magnetron.

If you consider the electrical circuit of a microwave oven (for example, Samsung) from the inside, it becomes clear that these developments migrated to the household appliances segment from heavy industry. Various types devices differ only externally. So, for example, the diagram of an LG microwave oven will not differ much from the diagram of a Daewoo brand microwave oven.

Here's how a microwave oven works: as the magnetron operates, it begins to release energy, which is converted into heat and used as targeted heating. This type The device operates from an anode-heated transformer-stabilizer. At first, this particular part was the most expensive in the production of a microwave oven. But over time, its cost dropped to an acceptable level, which made mass production of devices possible.

Considering internal structure microwaves, it is worth considering the design in more detail shunt magnetic circuit. This unit allows you to change the voltage increase within an error of 2% within the power supply fluctuation of 10%. Main feature transformer is the high inductive leakage force of the magnetic circuit. Perhaps in words the description of the operating principle of a microwave oven looks somewhat complicated, but in practice the device is quite simple.

At the time the design began, design engineers were faced with increased noise levels during operation of the microwave. In general, it is worth mentioning that high noise levels are a problem for many devices that are based on a unit for heat removal or cooling. Subsequently, this problem, of course, was solved, and quite in an interesting way. To eliminate increased vibration, some parts began to be connected by welding.

The construction of a microwave oven begins first with the body. In most cases it is rectangular box. This was done not because the designers suffer from a lack of imagination; the point here is in the specifics of operation.

When the microwave is turned on, the waves are not only directed towards the object being heated, they are also reflected from interior decoration housing, which significantly increases the thermal effect.

The rotating part – the saucer – also allows you to optimize the heating process. As it rotates, the waves are distributed evenly over the entire surface of the heated object. A wave entering a tank with products always has different shape – this is another specific feature of microwave ovens. Some waves are nodal, others are formed in the form of beams, so the impact is chaotic in nature, but optimization measures make it possible to level out this process.

Over the entire history of the existence of this type of device, the process of their manufacture, thermal effects and its optimization have been honed by manufacturers to an ideal state. Today, a microwave oven is a complete device, completely ready for use, reliable and safe, which is confirmed by many certificates from international observation consortia that regulate the harmful effects of technology on the human body.

Important function of the microwave door

No less attention is paid to the door during production. In microwave ovens, the door is not only decorative element, but also serves as a kind of fuse. The principle is very simple: if you open the door, the lock is activated and the operation of the units stops. Despite its apparent simplicity, the design of the door is quite complicated, because it is associated with the safe operation of the entire device.

So, let's take a closer look at how a microwave oven door works:

Firstly, the manufacturer needs to ensure that the door and body of the device fit perfectly against each other with a minimum angle. Large gaps prevent the device from being used. The reason is simple, the door serves as a kind of microwave shield, and if the gap is large enough, the radiation can penetrate beyond the cooking chamber. What radiation is and what its dangers are has been known for a long time.
Secondly, the perimeter of the door is equipped with a high-frequency throttle. This device serves to reduce radiation to an acceptable level.
Thirdly, at the moment of casting the door body, many additives are added, with the help of which it is achieved high percentage absorption of radiation. Of course, one cannot be completely sure of 100% absorption of radiation, but there is no doubt that residual waves do not pose a danger or significant harm to human health.

Over the entire history of the device’s existence, this part of the microwave has not undergone any major changes. Overall it's always two handles, one of which is responsible for the temperature, and the other for the cooking time. Of course, today you can find many different modifications: from simple “wheels” to control units, which will have many various functions. But their essence often comes down to an old and proven principle, nothing new in the device microwave ovens for the entire time of their existence has not been invented. The fundamental difference may only lie in the concept of controlling the device.

Now many manufacturers (for example, Samsung) rely on the innovative component and integrate touch panels management.

A little about the dangers of microwaves

Disputes about them have not subsided since their launch into mass production. Today there is no reliable information, confirming the harm from using this type of device.

Do not forget that a microwave oven does not emit radioactive waves. On the contrary, a microwave allows you to cook foods without losing their beneficial properties. The food is healthier because... it retains up to 80% of vitamins and minerals.

Traditional ovens and stoves cannot boast of this result. If you operate the device strictly according to the rules, then there is no danger from its operation. This conclusion is confirmed by the way the microwave oven is designed, as mentioned above.

It is not healthy food cooked in a microwave oven (so-called fast food) that can cause harm, and thermal microwave exposure has absolutely nothing to do with it. The harm of pies (and other flour products) lies not in the fact that they are cooked in the oven, but in their increased calorie content and slow absorption by the body.

The operating frequency of your microwave, which is also mentioned when it comes to harm, also does not play any significant role. It (the frequency) can change as much as you like, but this (contrary to popular misconception) will not lead to an increase or decrease in radiation, the background remains the same.

Conclusion

The conclusion that suggests itself: a microwave is a very simple, but at the same time indispensable device in the kitchen that makes our life easier every day. It is convenient and unpretentious to use and maintain, easy to clean, takes up little space and consumes very little energy. The structure of the microwave, as discussed above, remains unchanged: magnetron, I/O transformer, I/O capacitor, cooler and cooking chamber. The reliability of this technique has been proven in practice over several decades.

The microwave oven has firmly entered into everyday life and has become one of the indispensable attributes of any apartment. This household appliance allows you to heat or cook food in a matter of minutes using radiation invisible to the eye.

But to find out where this radiation comes from and how safe it is for humans, it is necessary to understand the structure and operating principle of the microwave oven magnetron, which is a generator of high-frequency waves.

Magnetron

What are microwaves and how do they heat food?

It's called microwave electromagnetic radiation with a wavelength from 1 mm to 1 m. This type radiation is used not only for domestic purposes, but also in navigation and radar systems, and in addition ensures the operation cellular communication and satellite television.

Microwaves can be generated either artificially or in a natural way(for example, on the Sun). Another name for microwaves is ultra-high frequency radiation, or microwave.

All types of household microwave ovens have a single radiation frequency of 2450 MHz. This value is international standard, which home appliance manufacturers must strictly adhere to to ensure that their products do not interfere with the operation of other microwave devices.

Microwave radiation

The thermal effects of microwave radiation were discovered by American physicist Percy Spencer in 1942. It was he who patented the use of a device generating microwaves for cooking, thereby laying the foundation for the use of microwave ovens in everyday life.

Over the next few decades, this technology was brought to perfection, which made it possible to establish mass production of simple and inexpensive devices for fast use.

To heat any material in a microwave oven, it must contain dipole molecules, that is, molecules that have opposite electric charges on both ends.

In food products, their main source is water. Under the influence of ultrahigh frequency radiation, these molecules begin to line up along power lines electromagnetic field, changing its direction about 5 billion times per second. The friction that arises between them is accompanied by the release of heat, which heats the food.

However, microwaves are not able to penetrate deeper than 2-3 cm from the surface of the product, so everything that is under this layer is heated due to thermal conductivity from the heated areas.

Heating food using a microwave

Magnetron design and its application

In most types of microwave technology, the generator of microwave oscillations is a magnetron. Devices similar in their principle of operation - klystrons and platinotrons - have not become so widespread. The magnetron was first used in microwave ovens in 1960. The most commonly used in technology is a multicavity magnetron, consisting of several components:

Anode. It is a copper cylinder divided into sectors with thick metal walls. These volumetric cavities are resonators that create a ring system of oscillations. A voltage of about 4000 volts is applied to the anode.
Cathode. It is located in the central part of the magnetron and is a cylinder containing an incandescent filament. Electron emission occurs in this part of the device. A voltage of 3 volts is supplied to the heater (filament).
Ring magnets. Electromagnets or permanent magnets high power located at the end parts of the device are necessary to create a magnetic field directed parallel to the magnetron axis. The movement of electrons also occurs in this direction.
Wire loop. It is connected to the cathode, fixed in the resonator and brought to the emitter antenna. The loop serves to output microwave radiation into a waveguide, after which it enters directly into the microwave chamber.

Magnetron device

Due to their simplicity of design and low cost, magnetrons have found application in many areas, but they are most widespread:

In microwave ovens. In addition to quickly cooking and defrosting food in household ovens, magnetrons also allow production tasks. An industrial microwave oven can perform heating, drying, melting, roasting and more. It is important to remember that the microwave cannot be turned on empty, since in this case the radiation will not be absorbed by anything and will return back to the waveguide, which can lead to its breakdown.
In radar. The radar antenna connected to the waveguide is actually a conical feed and is used in conjunction with a parabolic reflector (dish). The magnetron produces powerful short pulses of energy with a short wavelength, part of which, when reflected, is again sent to the antenna and then to a sensitive receiver, which processes the signal and displays it on the screen.

Magnetrons in radar

Magnetron operating principle

The operation of a microwave oven is based on the conversion of electrical energy into ultra-high frequency electromagnetic radiation, which sets in motion water molecules in food. Dipole molecules, constantly changing direction, generate heat, which allows you to quickly heat food while preserving it beneficial properties. The device that generates microwaves is a magnetron.

A magnetron, in fact, is an electric vacuum diode that uses the phenomenon of thermionic emission. This phenomenon occurs during the heating of the surface of the emitter or cathode. Under the influence of high temperature, the most active electrons tend to leave its surface, but this will only happen when voltage is applied to the anode. In this case, an electric field arises, and electrons begin to move towards the anode, moving along its field lines. If electrons find themselves in the zone of action of a magnetic field, then their trajectories deviate towards the direction of the field lines.

Electrovacuum diode

The magnetron anode has the shape of a cylinder with a system of cavities, or resonators, inside which there is a cathode with an incandescent filament. Two ring magnets located at the edges of the anode create a magnetic field inside the anode, due to which the electrons do not move directly from the cathode to the anode, but change their trajectory, rotating around the cathode. Near the resonators, electrons give them part of their energy, which leads to the formation of a powerful microwave field in their cavities, which is brought out using a wire loop connected to the emitter antenna.

To activate the magnetron, it is necessary to apply to the anode high voltage about 3-4 thousand volts. Therefore, the connection of the magnetron to the household electrical network is carried out using high voltage transformer. In addition, the microwave oven circuit includes a waveguide that transmits radiation inside the chamber, a switching circuit, a control unit, as well as protection and cooling elements. In addition, the internal walls of the chamber and a thin metal mesh on the device door prevent radiation from escaping beyond its boundaries.

Magnetron connection diagram

How does a magnetron affect microwave power?

Most modern manufacturers of microwave ovens offer the ability to select the power of the device. This parameter, in turn, determines the operating mode (defrosting or heating) and the speed of heating the food. However design features The magnetron does not allow its power to be reduced, therefore, to reduce the heating intensity, power is supplied to it at certain intervals. These pauses in the operation of the magnetron can be noticed if you turn on the microwave at medium power and listen to the sound of its operation.

Not long ago, some manufacturers of household appliances announced the appearance of a number of models of microwave ovens with an inverter power supply circuit. The use of this scheme made it possible not only to increase the amount of usable space in the chamber by reducing the dimensions of the emitter, but also to reduce the power consumption of the device. Unlike conventional models, the heating temperature in furnaces inverter type changes smoothly, but their cost is an order of magnitude higher.

Magnetron cooling and protection

During operation, the magnetron emits large number heat, so a radiator is installed on its body. Since overheating is the main cause of magnetron failure, other methods are used to protect it:

Thermal relay. This device is used to protect the magnetron, as well as the grill, if the model has one. The thermal fuse is equipped with a bimetallic strip that can be adjusted to a specific temperature. If this value is exceeded, it bends and opens the power circuit.
Fan. It not only blows cool air onto the magnetron radiator, but also performs a number of other functions. useful functions such as cooling electronic components devices, air circulation inside the chamber during operation of the grill, as well as the removal of hot steam to the outside through special openings.
Locking system. Several microswitches control the position of the microwave door, preventing the magnetron from turning on when it is open.

Thermal relay

Is it possible to replace the magnetron

The main advantage of modern magnetrons for household microwave ovens is their interchangeability. On various models Magnetrons produced by other companies will be suitable for microwave ovens, so they can be changed if necessary. At the same time, the only necessary requirement there will be a match in power. You can buy a magnetron in many electronics stores, but to make right choice, you need to understand its parameters and labeling. The following magnetron models are most often installed in microwave ovens:

2M 213 (600 W rated power and 700 W under load);
2M 214 (1000 W);
2M 246 (1150 W – highest power).

Even after studying all the necessary parameters of this device, it is not recommended to replace the magnetron at home. Firstly, it will be quite difficult to remove it yourself, and secondly, to ensure it safe work After installation, only a qualified specialist can do it.

Standard magnetron configuration

Diagnosis of faults and causes of their occurrence

Replacing the magnetron may require quite significant financial costs, so before you buy a new device, you need to diagnose the old one to make sure that it is really faulty. The test can be done at home using a regular tester. To do this you will need:

Disconnect the microwave from the electrical outlet.
Remove the protective cover and carry out visual inspection details.
“Ring” the main elements printed circuit board using a tester or multimeter.
Inspect the thermostat.

Diagnostics

At the end of the diagnostics, conclusions can be drawn about the malfunction of certain parts. The main reasons for magnetron failure include the following:

Vacuum tube cap is faulty. You can replace it yourself by simply selecting a similar cap from another magnetron. The seats of such caps have a standard configuration.
Heater breakage. When or her incorrect loading The magnetron will overheat, which can lead to excessive heating of the filament and its breakage. To diagnose it, it is necessary to measure the resistance between the legs of the capacitor. If its value is within 5-7 Ohms, then the heater is working.
Breakdown of the feed-through capacitor. If the tester does not show an “infinite” resistance value between its contacts, then the capacitor must be replaced.