Is a microwave oven dangerous to human health: truth or myth? Tamed invisibles. all about microwave ovens

Good afternoon, dear Khabrovsk residents.

This post will be about the undocumented functions of the microwave oven. I'll show you how many useful things you can do if you use a slightly modified microwave in an unconventional way.

The microwave contains a generator of microwave waves of enormous power.

The power of the waves that are used in the microwave has been exciting my consciousness for a long time. Its magnetron (microwave generator) produces electromagnetic waves with a power of about 800 W and a frequency of 2450 MHz. Just imagine, one microwave produces as much radiation as 10,000 wi-fi routers, 5,000 mobile phones or 30 mobile phone towers! To prevent this power from escaping, the microwave uses a double protective screen made of steel.

I open the case

I want to warn you right away that electromagnetic radiation in the microwave range can harm your health, and high voltage can cause death. But that won't stop me.
Removing the cover from the microwave, you can see a large transformer: MOT. It increases the mains voltage from 220 volts to 2000 volts to power the magnetron.

In this video I want to show what this voltage can do:

Antenna for magnetron

After removing the magnetron from the microwave, I realized that I couldn’t just turn it on. The radiation will spread from it in all directions, affecting everything around. Without hesitation, I decided to make a directional antenna from a coffee can. Here's the diagram:

Now all the radiation is directed in the right direction. Just in case, I decided to test the effectiveness of this antenna. I took a lot of small neon bulbs and laid them out on a plane. When I brought the antenna with the magnetron on, I saw that the lights were lighting up exactly where needed:

Unusual experiences

I would like to note right away that microwaves have a much stronger effect on technology than on people and animals. Even 10 meters from the magnetron, the equipment experienced severe malfunctions: the TV and music center made a terrible growling sound, the mobile phone first lost the network, and then completely froze. The magnetron had a particularly strong influence on wi-fi. When I brought the magnetron close to the music center, sparks fell from it and, to my surprise, it exploded! Upon closer inspection, I discovered that the mains capacitor had exploded. In this video I show the process of assembling the antenna and the effect of the magnetron on technology:

Using non-ionizing radiation from a magnetron, plasma can be obtained. In an incandescent lamp brought to the magnetron, a brightly glowing yellow ball, sometimes with a purple tint, like ball lightning, lights up. If you do not turn off the magnetron in time, the light bulb will explode. Even an ordinary paper clip turns into an antenna under the influence of microwaves. An EMF of sufficient strength is induced on it to ignite an arc and melt this paper clip. Fluorescent lamps and housekeepers light up at a fairly large distance and glow right in your hands without wires! And in a neon lamp, electromagnetic waves become visible:

I want to reassure you, my readers, that none of my neighbors suffered from my experiments. All the closest neighbors fled the city as soon as fighting began in Lugansk.

Safety precautions

I strongly do not recommend repeating the experiments I described because special precautions must be taken when working with microwaves. All experiments were performed solely for scientific and informational purposes. The harm of microwave radiation to humans has not yet been fully studied. When I came close to the working magnetron, I felt heat, like from an oven. Only from the inside and, as it were, pointwise, in waves. I didn't feel any further harm. But I still strongly do not recommend pointing a working magnetron at people. Due to the thermal effect, the protein in the eyes can coagulate and a blood clot may form. There is also debate that such radiation can cause cancer and chronic diseases.

Unusual uses of the magnetron

1 - Pest burner. Microwave waves effectively kill pests, both in wooden buildings and on the sunbathing lawn. Bugs have a moisture-containing interior under their hard shell (what an abomination!). Its waves instantly turn into steam, without causing harm to the tree. I tried killing pests on a living tree (aphids, moths), it was also effective, but it is important not to overdo it because the tree also heats up, but not so much.
2 - Metal melting. The magnetron power is quite enough for melting non-ferrous metals. You just need to use good thermal insulation.
3 - Drying. You can dry cereals, grains, etc. The advantage of this method is sterilization; pests and bacteria are killed.
4 - Cleaning up from wiretapping. If you treat a room with a magnetron, you can kill all the unwanted electronics in it: hidden video cameras, electronic bugs, radio microphones, GPS tracking, hidden chips and the like.
5 - Jammer. With the help of a magnetron you can easily calm even the noisiest neighbor! The microwave penetrates up to two walls and “calms” any sound equipment.

These are not all possible applications that I have tested. Experiments continue and soon I will write an even more unusual post. Still, I want to point out that using a microwave like this is dangerous! Therefore, it is better to do this in cases of extreme necessity and while observing safety rules when working with microwaves.

That's all for me, be careful when working with high voltage and microwaves.

V. KOLYADA. The material was prepared by the editors of "We Buy from A to Z" at the request of the magazine "Science and Life".

Science and life // Illustrations

Rice. 1. Electromagnetic radiation scale.

Rice. 2. Dipole molecules: a - in the absence of an electric field; b - in a constant electric field; c - in an alternating electric field.

Rice. 3. Penetration of microwaves deep into a piece of meat.

Rice. 4. Labeling of dishes.

Rice. 5. Attenuation of microwave radiation energy in the atmosphere: on each subsequent line, as you move away from the furnace, the radiation power is 10 times less than on the previous one.

Rice. 6. Basic elements of a microwave oven.

Rice. 7. Microwave oven door.

Rice. 8. Oven with a dissector (a) and a turntable (b).

In the second half of the twentieth century, ovens came into use in which food is heated by invisible rays - microwaves.

Like many other discoveries that have had a significant impact on people's daily lives, the discovery of the thermal effects of microwaves happened by accident. In 1942, American physicist Percy Spencer worked in the laboratory of the Raytheon company with a device that emitted ultrahigh-frequency waves. Different sources describe differently the events that happened that day in the laboratory. According to one version, Spencer put his sandwich on the device, and after removing it a few minutes later, he discovered that the sandwich had warmed up to the middle. According to another version, the chocolate that Spencer had in his pocket when he was working near his installation warmed up and melted, and, struck by a lucky guess, the inventor rushed to the buffet for raw corn kernels. The popcorn brought to the installation soon began to burst with a bang...

One way or another, the effect was discovered. In 1945, Spencer received a patent for the use of microwaves for cooking, and in 1947, the first devices for cooking using microwaves appeared in the kitchens of hospitals and military canteens, where the requirements for food quality were not so high. These Rytheon products, human-sized, weighed 340 kg and cost $3,000 apiece.

It took a decade and a half to perfect the oven, in which food is cooked using invisible waves. In 1962, the Japanese company Sharp launched the first mass-produced microwave oven, which, however, did not initially cause a consumer stir. The same company developed a rotating table in 1966, used a microprocessor oven control system for the first time in 1979, and developed the first microwave oven with Internet access in 1999.

Today, dozens of companies produce household microwave ovens. In the United States alone, 12.6 million microwave ovens were sold in 2000, not including combination ovens with a built-in microwave source.

The experience of using millions of microwave ovens in many countries over the past decades has proven the undeniable convenience of this method of cooking - speed, efficiency, ease of use. The very mechanism of cooking food using microwaves, which we will introduce you to below, determines the preservation of the molecular structure, and therefore the taste of the products.

What are microwaves

Microwave, or ultra-high frequency (MHF), radiation is electromagnetic waves with a length of one millimeter to one meter, which are used not only in microwave ovens, but also in radar, radio navigation, satellite television systems, cellular telephony, etc. Microwaves exist in nature, they are emitted by the Sun.

The place of microwaves on the scale of electromagnetic radiation is shown in Fig. 1.

Household microwave ovens use microwaves with a frequency f of 2450 MHz. This frequency is established for microwave ovens by special international agreements so as not to interfere with the operation of radars and other devices that use microwaves.

Knowing that electromagnetic waves travel at the speed of light With, equal to 300,000 km/s, it is easy to calculate what the wavelength is L microwave radiation of a given frequency:

L = c/f= 12.25 cm.

To understand the principle of operation of a microwave oven, you need to remember one more fact from a school physics course: a wave is a combination of alternating fields - electric and magnetic. The foods we eat do not have magnetic properties, so we can forget about the magnetic field. But the changes in the electric field that the wave brings with it are very useful for us...

How do microwaves heat food?

Food contains many substances: mineral salts, fats, sugar, water. To heat food using microwaves, it must contain dipole molecules, that is, those that have a positive electrical charge at one end and a negative one at the other. Fortunately, there are plenty of such molecules in food - these are molecules of fats and sugars, but the main thing is that the dipole is a molecule of water - the most common substance in nature.

Every piece of vegetables, meat, fish, and fruit contains millions of dipole molecules.

In the absence of an electric field, the molecules are arranged randomly (Fig. 2a).

In an electric field, they line up strictly in the direction of the field lines, “plus” in one direction, “minus” in the other. As soon as the field changes direction to the opposite, the molecules immediately turn over 180° (Fig. 2, b).

Now remember that the frequency of microwaves is 2450 MHz. One hertz is one vibration per second, a megahertz is one million vibrations per second. During one wave period, the field changes its direction twice: it was “plus”, became “minus”, and the original “plus” returned again. This means that the field in which our molecules are located changes polarity 4,900,000,000 times per second! Under the influence of microwave radiation, molecules tumble at a frantic frequency and literally rub against each other during revolutions (Fig. 2, c). The heat released during this process is what causes the food to warm up.

Microwaves heat up food in much the same way that our palms heat up when we quickly rub them together. There is one more similarity: when we rub the skin of one hand against the skin of the other, heat penetrates deep into the muscle tissue. So are microwaves: they work only in a relatively small surface layer of food, without penetrating deeper than 1-3 cm (Fig. 3). Therefore, heating of products occurs due to two physical mechanisms - heating of the surface layer by microwaves and subsequent penetration of heat into the depths of the product due to thermal conductivity.

This immediately follows a recommendation: if you need to cook, for example, a large piece of meat in the microwave, it is better not to turn on the oven at full power, but to work at medium power, but increase the time the piece remains in the oven. Then the heat from the outer layer will have time to penetrate deep into the meat and cook the inside of the piece well, and the outside of the piece will not burn.

For the same reasons, it is better to stir liquid foods, such as soups, periodically, removing the pan from the oven from time to time. This will help the heat penetrate deep into the soup container.

Microwave dishes

Different materials behave differently in relation to microwaves, and not all dishes are suitable for a microwave oven. Metal reflects microwave radiation, so the inner walls of the oven cavity are made of metal so that it reflects the waves towards the food. Accordingly, metal utensils are not suitable for microwaves.

The exception is low, open metal utensils (such as aluminum food trays). Such dishes can be placed in a microwave oven, but, firstly, only downwards, to the very bottom, and not on the second highest level (some microwave ovens allow “two-story” placement of trays); secondly, it is necessary that the oven does not operate at maximum power (it is better to increase the operating time), and the edges of the tray are at least 2 cm away from the walls of the chamber so that an electric discharge does not form.

Glass, porcelain, dry cardboard and paper allow microwaves to pass through (wet cardboard will begin to heat up and will not allow microwaves to pass through until it dries). Glassware can be used in the microwave, but only if it can withstand the high heating temperature. For microwave ovens, dishes are made from special glass (for example, Pyrex) with a low coefficient of thermal expansion and resistant to heat.

Recently, many manufacturers have provided cookware with markings indicating that they are suitable for use in a microwave oven (Fig. 4). Before using the cookware, pay attention to its labeling.

Please note that, for example, plastic heat-resistant food containers are excellent at transmitting microwaves, but they may not withstand high temperatures if you also turn on the grill in addition to the microwaves.

Food absorbs microwaves. Clay and porous ceramics behave the same way, which are not recommended for use in microwaves. Dishes made from porous materials retain moisture and heat themselves instead of allowing microwaves to pass through to the food. As a result, less microwave energy reaches the food and you risk getting burned when removing it from the oven.

Here are three main rules on the topic: what should not be put in the microwave.

1. Do not place dishes with gold or other metal rims in the microwave. The fact is that the alternating electric field of microwave radiation leads to the appearance of induced currents in metal objects. By themselves, these currents are nothing terrible, but in a thin conductive layer, such as a layer of decorative metal coating on dishes, the density of induced currents can be so high that the rim, and with it the dishes, will overheat and be destroyed.

In general, there is no place in a microwave oven for metal objects with sharp edges or pointed ends (for example, forks): the high density of induced current on the sharp edges of the conductor can cause melting of the metal or the appearance of an electric discharge.

2. Under no circumstances should you place tightly closed containers in the microwave: bottles, cans, food containers, etc., as well as eggs(no matter raw or cooked). All of the above items can rupture when heated and render the oven unusable.

Items that can rupture when heated include foods that have skin or casing, such as tomatoes, sausages, sausages, etc. To avoid explosive expansion of these foods, pierce the shell or skin with a fork before placing them in the oven. Then the steam formed inside during heating can easily come out and will not tear the tomato or sausage.

3. And the last thing: it is impossible for the microwave to be... empty. In other words, You can’t turn on an empty stove, without a single object that would absorb microwaves. A simple and understandable unit is adopted as the minimum load for the oven whenever it is turned on (for example, when checking its functionality): a glass of water (200 ml).

Turning on an empty microwave oven may seriously damage it. Without encountering any obstacles in their path, microwaves will be repeatedly reflected from the inner walls of the oven cavity, and the concentrated radiation energy can damage the oven.

By the way, if you want to bring water in a glass or other tall narrow vessel to a boil, do not forget to put a teaspoon in it before putting the glass in the oven. The fact is that boiling water under the influence of microwaves does not occur in the same way as, for example, in a kettle, where heat is supplied to the water only from below, from the bottom. Microwave heating occurs from all sides, and if the glass is narrow, almost throughout the entire volume of water. In a kettle, water boils when it boils, as bubbles of air dissolved in the water rise from the bottom. In the microwave, the water will reach boiling temperature, but there will be no bubbles - this is called the delayed boiling effect. But when you take the glass out of the oven, shaking it at the same time, the water in the glass will belatedly begin to boil, and the boiling water can scald your hands.

If you do not know what material the cookware is made of, do a simple experiment that will allow you to determine whether it is suitable for this purpose or not. Of course, we are not talking about metal: it is not difficult to identify. Place the empty dish in the oven next to a glass filled with water (don't forget the spoon!). Turn on the oven and let it run for one minute at maximum power. If the dishes remain cold after this, it means they are made of microwave-transparent material and can be used. If the cookware gets hot, it means it is made of microwave-absorbing material and you are unlikely to be able to cook food in it.

Are microwaves dangerous?

There are a number of misconceptions associated with microwave ovens, which are explained by a lack of understanding of the nature of this type of electromagnetic waves and the mechanism of microwave heating. We hope that our story will help overcome such prejudices.

Microwaves are radioactive or make foods radioactive. This is incorrect: microwaves are classified as non-ionizing radiation. They do not have any radioactive effect on substances, biological tissues and food.

Microwaves change the molecular structure of foods or make foods carcinogenic.

This is also incorrect. Microwaves operate on a different principle than X-rays or ionizing radiation, and they cannot make foods carcinogenic. In contrast, because microwave cooking requires very little fat, the finished meal contains less burnt fat with its molecular structure altered by cooking. Therefore, cooking food using microwaves is healthier and does not pose any danger to humans.

Microwave ovens emit dangerous radiation.

This is not true. Although direct exposure to microwaves can cause thermal damage to tissue, there is absolutely no risk when using a working microwave oven. The design of the oven provides strict measures to prevent radiation from escaping outside: there are duplicate devices for blocking the microwave source when the oven door is opened, and the door itself prevents microwaves from escaping outside the cavity. Neither the housing, nor any other part of the oven, nor food products placed in the oven accumulate electromagnetic radiation in the microwave range. As soon as the oven is turned off, the emission of microwaves stops.

Those who are afraid to even come close to a microwave oven need to know that microwaves attenuate very quickly in the atmosphere. To illustrate, we give the following example: the microwave radiation power allowed by Western standards at a distance of 5 cm from a new, just purchased stove is 5 milliwatts per square centimeter. Already at a distance of half a meter from the microwave, the radiation becomes 100 times weaker (see Fig. 5).

As a consequence of such strong attenuation, the contribution of microwaves to the general background of electromagnetic radiation surrounding us is no higher than, say, from a TV, in front of which we are ready to sit for hours without any fear, or a mobile phone, which we so often hold to our temple. Just don't lean your elbow on a running microwave or lean your face against the door trying to see what's going on in the cavity. It is enough to move away from the stove at arm's length, and you can feel completely safe.

Where do microwaves come from?

The source of microwave radiation is a high-voltage vacuum device - magnetron. In order for the magnetron antenna to emit microwaves, a high voltage (about 3-4 kW) must be applied to the magnetron filament. Therefore, the mains supply voltage (220 V) is not enough for the magnetron, and it is powered through a special high-voltage transformer(Fig. 6).

The magnetron power of modern microwave ovens is 700-850 W. This is enough to bring a 200 gram glass of water to a boil in a few minutes. To cool the magnetron, there is a fan next to it that continuously blows air over it.

The microwaves generated by the magnetron enter the oven cavity through waveguide- a channel with metal walls that reflect microwave radiation. In some microwaves, waves enter the cavity only through one hole (usually under the “ceiling” of the cavity), in others - through two holes: at the “ceiling” and at the “bottom”. If you look into the cavity of the oven, you can see mica plates that cover the holes for introducing microwaves. The plates do not allow splashes of fat to enter the waveguide, and they do not interfere with the passage of microwaves at all, since mica is transparent to radiation. Over time, mica plates become saturated with grease, become loose, and need to be replaced with new ones. You can cut a new plate from a sheet of mica yourself in the shape of the old one, but it is better to buy a new plate at a service center that services equipment of this brand, since it is inexpensive.

The microwave cavity is made of metal, which may have one or another coating. In the cheapest models of microwave ovens, the inner surface of the cavity walls is coated with enamel paint. This coating is not resistant to high temperatures, so it is not used in models where, in addition to microwaves, food is heated by a grill.

Coating the cavity walls with enamel or special ceramics is more durable. Walls with this coating are easy to clean and can withstand high temperatures. The disadvantage of enamel and ceramics is their fragility in relation to impacts. When placing dishes in the microwave cavity, it is easy to accidentally hit the wall, and this can damage the coating applied to it. Therefore, if you purchased a microwave oven with enamel or ceramic wall coating, handle it with care.

The most durable and impact-resistant walls are made of stainless steel. The advantage of this material is its excellent reflection of microwaves. The downside is that if the housewife does not pay too much attention to cleaning the internal cavity of the microwave oven, then splashes of fat and food that are not removed in time can leave marks on the stainless surface.

The cavity volume of a microwave oven is one of the important consumer characteristics. Compact ovens with a cavity volume of 8.5-15 liters are used for defrosting or preparing small portions of food. They are ideal for single people or for special tasks such as warming up a baby bottle. Stoves with a cavity volume of 16-19 liters are suitable for a married couple. You can place a small chicken in this oven. Medium-sized stoves have a cavity volume of 20-35 liters and are suitable for a family of three to four people. Finally, for a large family (five to six people) you need a microwave oven with a cavity volume of 36-45 liters, which allows you to bake a goose, turkey or a large pie.

A very important element of a microwave oven is the door. It should make it possible to see what is happening in the cavity, and at the same time prevent microwaves from escaping outside. The door is a multilayer cake made of glass or plastic plates (Fig. 7).

In addition, between the plates there is always a mesh made of perforated metal sheet. The metal reflects microwaves back into the oven cavity, and the perforations that make it transparent for viewing have a diameter of no more than 3 mm. Let us remember that the wavelength of microwave radiation is 12.25 cm. It is clear that such a wave cannot pass through three-millimeter holes.

To prevent radiation from finding loopholes where the door is adjacent to the cut of the cavity, a seal made of dielectric material. It fits tightly to the front end of the microwave oven body when the door is closed. The thickness of the seal is about a quarter of the wavelength of microwave radiation. Here we use a calculation based on the physics of waves: as we know, waves in antiphase cancel each other out. Thanks to the precisely selected thickness of the sealant, the so-called negative interference of the wave penetrating inside the sealant material and the reflected wave coming out of the sealant is ensured. Thanks to this, the seal serves as a trap that reliably dampens radiation.

To completely eliminate the possibility of generating microwaves when the chamber door is open, a set of several independent switches that duplicate each other is used. These switches are closed by contact pins on the oven door and break the magnetron power supply circuit even if the door is slightly loose.

Taking a closer look at the microwave ovens displayed in the sales area of a large household appliance store, you will notice that they differ in the direction the door opens: on some ovens the door opens to the side (usually to the left), while on others it tilts towards you, forming a small shelf. The latter option, although less common, provides additional convenience when using the oven: the horizontal plane of the open door serves as a support when loading dishes into the oven cavity or when removing a finished dish. You just need to avoid overloading the door with excess weight and not leaning on it.

How to "stir" microwaves

Microwaves entering the oven cavity through a waveguide are chaotically reflected from the walls and sooner or later reach the products placed in the oven. At the same time, at each point of, say, a chicken carcass that we want to defrost or fry, waves come from a variety of directions. The trouble is that the interference we have already mentioned can work both in “plus” and “minus”: waves arriving in phase will reinforce each other and warm up the area where they hit, and those arriving in antiphase will cancel each other out, and there will be no use from them.

In order for the waves to penetrate the products evenly, they must be “mixed,” as it were, in the cavity of the oven. It is better for the products themselves to literally spin around in the cavity, exposing different sides to the radiation flow. So it appeared in microwave ovens turntable- a dish resting on small rollers and driven by an electric motor (Fig. 8, b).

You can “stir” microwaves in different ways. The simplest and most straightforward solution is to hang a stirrer under the “ceiling” of the cavity: a rotating impeller with metal blades that reflect microwaves. Such a mixer is called a dissector (Fig. 8, a). It is good for its simplicity and, as a result, low cost. But, unfortunately, microwave ovens with a mechanical microwave reflector are not distinguished by high uniformity of the wave field.

The combination of a rotating dissector and a food turntable is sometimes given a special name. So, in Miele microwave ovens this is called the Duplomatic system.

Some microwave ovens (for example, models Y82, Y87, ET6 from Moulinex) have two turntables located one above the other. This system is called DUO and allows you to cook two dishes at the same time. Each table has a separate drive through a socket on the rear wall of the oven cavity.

A more subtle, but also effective way to achieve a uniform wave field is to carefully work on the geometry of the internal cavity of the furnace and create optimal conditions for the reflection of waves from its walls. Each oven manufacturer has its own “brand name” for such “advanced” microwave distribution systems.

Magnetron operating schedule

Any microwave oven allows the owner to set the power required to perform a particular function: from the minimum power sufficient to keep food warm, to the full power needed to cook food in an oven loaded with food.

A feature of magnetrons used in most microwave ovens is that they cannot “burn at full heat.” Therefore, in order for the oven to operate not at full, but at reduced power, you can only periodically turn off the magnetron, stopping the generation of microwaves for some time.

When the oven is operating at minimum power (let it be 90 W, while keeping the food in the oven cavity warm), the magnetron is turned on for 4 seconds, then off for 17 seconds, and these on-off cycles alternate all the time.

Let's increase the power, say, to 160 W if we need to defrost food. Now the magnetron turns on for 6 s and turns off for 15 s. Let's add power: at 360 W, the duration of the on and off cycles is almost equal - this is 10 s and 11 s, respectively.

Note that the total duration of the magnetron on and off cycles remains constant (4 + 17, 6 + 15, 10 + 11) and amounts to 21 s.

Finally, if the furnace is turned on at full power (in our example this is 1000 W), the magnetron operates constantly without turning off.

In recent years, models of microwave ovens have appeared on the domestic market in which the magnetron is powered through a device called an “inverter.” Manufacturers of these ovens (Panasonic, Siemens) emphasize such advantages of the inverter circuit as the compactness of the microwave radiation unit, which makes it possible to increase the volume of the cavity while maintaining the same external dimensions of the oven and more efficient conversion of consumed electricity into microwave energy.

Inverter power systems are widely used, for example, in air conditioners and allow you to smoothly change their power. In microwave ovens, inverter power systems make it possible to smoothly change the power of the radiation source, instead of turning it off every few seconds.

Due to the smooth change in the power of the microwave emitter in ovens with an inverter, the temperature also changes smoothly, unlike traditional ovens, where the radiation supply is stopped from time to time due to periodic switching off of the magnetron. However, let's be fair to traditional ovens: these temperature fluctuations are not that strong and are unlikely to affect the quality of the cooked food.

Just like air conditioners, microwaves with an inverter power system are more expensive than those with a traditional one.

Did you know...

that any milk can be heated in a microwave oven without any damage to its nutritional properties? The only exception is freshly expressed breast milk: under the influence of microwaves, it loses the components it contains that are vital for the baby.

that sometimes it is better to cancel the table rotation. This will allow you to cook large dishes (salmon, turkey, etc.), which simply cannot turn in the cavity without hitting its walls. Use the unrotate function if your microwave has one.

Since the creation of microwave ovens, debates have periodically flared up between physicists and medical specialists about the benefits and harms of this technical achievement. In fact, without certain knowledge about the effect of microwave oven radiation on the human body and the impact of microwaves on the food cooked in it, many people are afraid to use it.

It is worth noting that these fears are not groundless: a useful invention for the kitchen can indeed become unsafe under certain conditions. But if the operation of a microwave oven is organized in accordance with all technical requirements, ultra-high-frequency waves will fulfill their culinary purpose without much harm to humans.

The principle of operation of a microwave oven

The process of heating food in a microwave is based on the effect of radiation generated by a magnetron on it. It is thanks to the ultra-high frequency of the microwave (2450 GHz - in contrast, for example, to the 50 Hz frequency of the current in the industrial power supply network) that heating is carried out almost instantly, which is the main advantage of the device.

The most important condition for successful heating of a product is the presence in it of dipoles - molecules with an uneven distribution of charges and a total electric charge equal to zero, due to the polar arrangement of positive and negative charges in the atom. The most striking representatives of dipoles include water molecules, which means that all products with high humidity will be more susceptible to the influence of microwaves. At the same time, vegetable oils do not have dipole molecules, so heating them in the microwave is impractical.

Thanks to the electromagnetic field created in the microwave oven, the dipoles inside the product rotate 180 degrees about 6 billion times per second. This incredible speed causes the molecules of the substance to undergo friction, which causes the internal temperature of the product to rise. It is in this physically explainable transformation of electrical radiation into thermal energy that many see the harm of microwaves.

Harm and benefits of a microwave oven

Some people believe that the direct radiation emanating from a microwave oven while it is on can harm someone nearby. Many explain this risk by the fact that the human body consists of more than 70% water, that is, dipole molecules that are particularly sensitive to the influence of microwaves. Because of this influence, the structure of water allegedly changes, as its ionization occurs (the appearance of an additional electron in a water atom or the loss of an existing one). Therefore, destruction and deformation of molecules occurs not only in the heated product, but also in the human body. However, this opinion is erroneous.

Science claims that the concept of “structure” in relation to water (namely water, not ice) is not applicable, which means that it is impossible to destroy or change its structure.

The Internet is filled with such slogans

Is there scientific evidence that microwave ovens are harmful?

A microwave oven is not always dangerous for humans, but only under specific circumstances. Direct damage can be caused by the cumulative effect of microwave radiation generated by the magnetron. This becomes possible only in two cases:

If the shutdown mechanism does not work when the door is opened or not tightly closed. Manufacturers convince that the device has double guaranteed protection of the consumer from unwanted radiation, however, the automatic shutdown system occasionally fails.
If, as a result of carbon deposits or other reasons, the door seal is compromised. Microwaves can leak through the smallest holes or cracks. These outwardly invisible defects most often appear after prolonged use of an electrical appliance.

The leakage of microwaves through unnoticeable cracks, and even more so through an open door when the generator is not turned off, can cause significant harm to a person, including burns to internal organs.

Symptoms of exposure to microwave waves

You can suspect that a person has been harmed by a microwave oven based on the following signs:

dizziness;
the appearance of signs of heart failure;
blurred vision;
drowsiness;
nervousness and reasonless crying (in children).

If such symptoms were detected after being near a working electrical appliance, this is an almost 100% signal that its housing has depressurized.

Methods for checking a microwave oven for radiation leakage

To check whether a microwave oven in use is dangerous or whether there is radiation leakage through invisible cracks in the door, you can use several popular methods. You can also use a special microwave radiation detector.

Manual verification methods

These methods, in the absence of a special device, are quite simple, but some of them do not always give reliable results. However, if you are unable to purchase a detector yet, you can check the oven as follows:

To carry out the most popular, but most unreliable method of testing for harmfulness, you will need two mobile phones. You need to put one of them in the microwave and close it tightly without turning it on. Then call it from another mobile phone. If it rings, it means that the waves are freely passing through the protective door both from the outside and from the inside.

Experts consider the disadvantage of this method to be the difference between the operating frequencies of microwave ovens and mobile phones, so it is unlikely that it will be possible to determine the harm or benefit of the device in this way.

Checking with a detector

The most reliable and effective test remains using a special device called a microwave radiation detector. Necessary:

Place a glass of cold water in the stove.
Close the door and turn on the oven.
Bring the detector closer to the door and slowly move it along the perimeter and diagonally of the door, stopping at the corners. In the absence of radiation, the instrument needle will be in the green zone, and the slightest leak will cause it to move to the red zone.

Recommendations for safe use of a microwave oven

It is known that as you move away from the microwave oven, the power of microwave wave energy quickly decreases, so it is safest to be at some distance from it while the microwave oven is operating.

Near the operating device (about 2 cm from the outer wall), the level of permissible radiation should not exceed 5 mW per 1 sq. cm.

A microwave, the harm and benefits of which depend on compliance with the operating rules, with such radiation is absolutely safe for the human body. However, there are other reasons why this kitchen appliance can cause harm. Therefore, you should consider the rules for handling it:

When operating an electrical appliance, stay away from it.
Do not place the microwave oven near the stove or the dining table.
Use only for quick defrosting and heating food.
Place heated products in an open, not hermetically sealed form (this even applies to sausages in thick cling film).
Do not place metal utensils or ceramic containers with metallic paint rims inside - this will cause an arc to occur that threatens the integrity of the magnetron and protective casing.
Make sure that the protective door is clean and do not allow carbon deposits to form on it, which could lead to depressurization of the housing.

People who have an implanted pacemaker should not use a microwave device.

Which dishes are not suitable for the microwave and why?

When operating a microwave oven, it is prohibited to use the following types of utensils:

Made of metal. Any of its types - cast iron, steel, brass, copper - reflect microwaves, preventing them from penetrating the product. In addition, being electrically conductive, they can provoke spark discharges and the formation of an electromagnetic field, which is dangerous for microwave ovens.
From glass and porcelain, if such dishes have a pattern applied with gold or other paint that may contain metals. Even a half-erased pattern may contain metal particles that, under the influence of a microwave, can spark and create a field.
Made of crystal. Its complex structure may contain particles of silver, lead and other metals; in addition, an obstacle to its use is the heterogeneity of thickness (faceted surface), due to which such dishes can shatter into pieces under the influence of microwaves.
It is not recommended to use disposable tableware made of thin plastic or waxed cardboard, unglazed ceramics, or plastic that is not resistant to high temperatures.

Even in a second, microwaves cause dipole molecules to rotate “around their axis” billions of times. Therefore, it is better not to risk either the dishes or the serviceability of the microwave oven itself, so that it works in the kitchen for a long time and safely.

Is a microwave oven dangerous to human health: truth or myth?

When microwave ovens first appeared, they were jokingly called a bachelor's appliance. If you follow this statement, then it is true for the first generation of kitchen appliances. However, nowadays, microwave ovens are equipped with a number of functions and unique features that deserve respect. It is very easy to control the device using a processor that operates in accordance with the set parameters. That is why it is important to familiarize yourself with all the nuances of this technique in order to make sure what effect it has on the human body.

Physical performance characteristics

Over the past few years, you can see a boom in microwave ovens. The harm of a microwave oven is not a myth, but a strict reality, which has been proven by doctors and scientists. This opinion is supported by materials whose scientific evidence confirms the negative impact of microwaves on the human body. Many years of scientific research into radiation from microwave ovens have established the level of harmful effects on human health.

Therefore, it is important to adhere to the rules of technical security means or TSO. Protective measures will help reduce the power of the pathogenic influence of microwave radiation. If you do not have the opportunity to provide optimal protection when using a microwave to prepare food, you are guaranteed harmful effects on the body. It is very important to know the basics of TSO and apply them when working in a microwave oven.

If we recall the basic physics course in the school curriculum, we can establish that the heating effect is possible due to the operation of microwave radiation on food. Whether you can eat such food or not is a rather difficult question. The only thing that can be said is that such food is of no benefit to the human body. For example, if you cook baked apples in a microwave oven, they will not bring any benefit. Baked apples are exposed to electromagnetic radiation, which operates in a certain microwave range.

The radiation source of microwave ovens is a magnetron.

The microwave radiation frequency can be considered to be in the range of 2450 GHz. The electrical component of such radiation is the effect on the dipole molecule of substances. As for a dipole, it is a kind of molecule that has opposite charges at different ends. The electromagnetic field is capable of rotating this dipole one hundred and eighty degrees in one second at least 5.9 billion times. This speed is not a myth, so it causes friction of molecules, as well as subsequent heating.

Microwave radiation can penetrate to a depth of less than three centimeters, subsequent heating occurs through heat transfer from the outer layer to the inner one. The brightest dipole is considered to be a water molecule, so food that contains liquid heats up much faster. A vegetable oil molecule is not a dipole, so they should not be heated in a microwave oven.

The wavelength of microwave radiation is about twelve centimeters. Such waves are located between infrared and radio waves, so they have similar functions and properties.

Microwave danger

The human body is capable of being exposed to a wide variety of radiation, so a microwave oven is no exception. You can argue for a long time about whether such food is beneficial or not. Despite the enormous popularity of this kitchen appliance, harm from a microwave oven is not a fiction or a myth, so you should listen to the advice on TSO, and, if possible, refuse to work with this stove. During use, you need to monitor the status of the indicator.

If you do not have the opportunity to protect your body from harmful energy, you can use high-quality protection, the basics of TSO, to protect your own health.

First, you need to find out the risk that microwave oven radiation may pose. Many nutritionists, doctors and physicists are engaged in restless debate regarding food prepared in this way. Ordinary baked apples will not bring any benefit, since they are exposed to harmful microwave energy.

That is why every person should become familiar with the possible negative health effects. The greatest harm to health from microwaves comes in the form of electromagnetic radiation that comes from the oven when it is running.

For the human body, a negative side effect can be deformation, as well as restructuring and destruction of molecules, and the formation of radiological compounds. In simple words, there is irreparable damage to the health and general condition of the human body, since non-existent compounds are formed that are affected by ultrahigh frequencies. In addition, you can observe the process of ionization of water, which transforms its structure.

According to some studies, such water is very harmful to the human body and all living things, as it becomes dead. For example, when watering a living plant with such water, it will simply die within a week!

This is why all products (even baked apples) that are heat-treated in the microwave become dead. According to this information, we can summarize briefly that food from the microwave has an adverse effect on the health and condition of the human body.

However, there is no precise evidence that can confirm this hypothesis. According to physicists, the wavelength is very short, so it cannot cause ionization, but only heating. If the door opens and the protection does not work, which turns off the magnetron, then the human body experiences the impact of the generator, which guarantees harm to health, as well as burns to internal organs, since the tissue is destroyed and experiences serious stress.

To protect yourself, protection must be at the highest level, so it is important to adhere to the TCO base. Do not forget that there are absorbing objects for these waves, and the human body is no exception.

Effect on the human body

According to studies of microwave rays, the moment they hit a surface, the tissue of the human body absorbs energy, which causes heating. As a result of thermoregulation, blood circulation increases. If the irradiation was general, then there is no possibility of instant heat removal.

Blood circulation has a cooling effect, so those tissues and organs that are depleted of blood vessels suffer the most. Basically, clouding occurs, as well as destruction of the lens of the eye. Such changes are irreversible.

The tissue that contains a large amount of liquid has the greatest absorption capacity:

blood;
intestines;
gastric mucosa;
lens of the eye;
lymph.

As a result, the following happens:

the efficiency of the exchange and adaptation process decreases;
the thyroid gland and blood are transformed;
the mental sphere changes. Over the years, there have been cases where the use of microwaves causes depression and suicidal tendencies.

How long does it take for the first symptoms of a negative impact to appear? There is a version according to which all the signs accumulate for quite a long time.

They may not appear for many years. Then a critical moment comes when the general status indicator loses ground and the following appear:

headaches;
nausea;
weakness and fatigue;
dizziness;
apathy, stress;
heart pain;
hypertension;
insomnia;
fatigue and much more.

So, if you do not follow all the rules of the TCO database, the consequences can be extremely sad and irreversible. It is difficult to answer the question of how long or years it takes for the first symptoms to appear, since it all depends on the microwave model, manufacturer, and the person’s condition.

Protection measures

According to TCO, the impact of a microwave depends on many nuances, most often these are:

wavelength;
duration of exposure;
use of specific protection;
types of rays;
intensity and distance from the source;
external and internal factors.

In accordance with TSO, you can defend yourself using several methods, namely individual and general. TCO measures:

change the direction of the rays;
reduce the duration of exposure;
remote control;
indicator status;
Protective shielding has been used for several years.

If it is not possible to follow TSO, you can guarantee that the condition will worsen in the future. TCO options are based on the functions of the furnace - reflection, as well as absorption capabilities. If there are no protective measures, it is necessary to use special materials that can repel the adverse effect. Such materials include:

multilayer bags;
shungite;
metallized mesh;
workwear made of metallized fabric - an apron and potholder, a cape equipped with glasses and a hood.

If you use this method, then there is no reason to worry for many years.

Apples in the microwave

Everyone knows that baked fruits and vegetables are very nutritious and healthy, baked apples are no exception. Baked apples are the most popular and delicious dessert, which is prepared not only in the oven, but also in the microwave. However, few people think that fruits baked in the microwave can be harmful.

Baked apples contain many vitamins and nutrients, giving them a more tender and juicy texture. Baked fruits are not harmful, so it is important to choose the cooking method. As it became known, baked apples in the microwave do not cause harm, since they do not ionize.

In simple words, baked apples are a very tasty, valuable food that can be cooked in a microwave oven without harm to health. If you do not follow the operating rules and neglect the indicator, you can harm your condition. Baked apples are very easy to prepare because the microwave reduces the cooking time. The indicator on the display is responsible for all other functions, so it is important to keep an eye on it.

This is important! If the indicator malfunctions, it cannot be repaired. The indicator is a special LED light bulb. That is why, thanks to the indicator, you can find out about the health of the device.

Answering the question whether microwave ovens are harmful - myth or reality, we can say for sure that this is not a myth. By following the proposed recommendations and operating rules, you will protect yourself from negative influences.

Contents of the article

ULTRA HIGH FREQUENCY RANGE, frequency range of electromagnetic radiation (100-300,000 million hertz), located in the spectrum between ultra-high television frequencies and frequencies of the far infrared region. This frequency range corresponds to wavelengths from 30 cm to 1 mm; therefore it is also called the decimeter and centimeter wave range. In English-speaking countries it is called the microwave band; This means that the wavelengths are very small compared to the wavelengths of conventional radio broadcasting, which are on the order of several hundred meters.

Since microwave radiation is intermediate in wavelength between light radiation and ordinary radio waves, it has some properties of both light and radio waves. For example, like light, it travels in a straight line and is blocked by almost all solid objects. Much like light, it is focused, spreads out as a beam, and reflected. Many radar antennas and other microwave devices are enlarged versions of optical elements such as mirrors and lenses.

At the same time, microwave radiation is similar to radio radiation in the broadcast ranges in that it is generated by similar methods. The classical theory of radio waves applies to microwave radiation, and it can be used as a means of communication based on the same principles. But thanks to higher frequencies, it provides greater opportunities for transmitting information, which makes communication more efficient. For example, one microwave beam can carry several hundred telephone conversations simultaneously. The similarity of microwave radiation to light and the increased density of information it carries have proven to be very useful for radar and other fields of technology.

APPLICATION OF MICROWAVE RADIATION

Radar.

Waves in the decimeter-centimeter range remained a subject of purely scientific curiosity until the outbreak of World War II, when there was an urgent need for a new and effective electronic means of early detection. Only then did intensive research into microwave radar begin, although its fundamental possibility was demonstrated back in 1923 at the US Naval Research Laboratory. The essence of radar is that short, intense pulses of microwave radiation are emitted into space, and then part of this radiation is recorded, returning from the desired distant object - a sea vessel or aircraft.

Connection.

Microwave radio waves are widely used in communications technology. In addition to various military radio systems, there are numerous commercial microwave communication lines in all countries of the world. Since such radio waves do not follow the curvature of the earth's surface but travel in a straight line, these communication links typically consist of relay stations installed on hilltops or radio towers at intervals of approx. 50 km. Parabolic or horn antennas mounted on towers receive and transmit microwave signals. At each station, the signal is amplified by an electronic amplifier before retransmission. Since microwave radiation allows highly targeted reception and transmission, transmission does not require large amounts of electricity.

Although the system of towers, antennas, receivers and transmitters may seem very expensive, in the end it all more than pays off thanks to the large information capacity of microwave communication channels. Cities across the United States are connected by a complex network of more than 4,000 microwave relay links, forming a communications system that stretches from one ocean coast to the next. The channels of this network are capable of transmitting thousands of telephone conversations and numerous television programs simultaneously.

Communications satellites.

The system of radio relay towers necessary for transmitting microwave radiation over long distances can, of course, only be built on land. For intercontinental communication, a different relay method is required. Here, connected artificial earth satellites come to the rescue; launched into geostationary orbit, they can perform the functions of microwave communication relay stations.

An electronic device called an active-relay satellite receives, amplifies, and relays microwave signals transmitted by ground stations. The first experimental satellites of this type (Telstar, Relay and Syncom) successfully relayed television broadcasts from one continent to another in the early 1960s. Based on this experience, commercial intercontinental and domestic communications satellites were developed. Intelsat's latest intercontinental series of satellites have been deployed to different points in geostationary orbit in such a way that their coverage areas overlap to provide service to subscribers around the world. Each Intelsat satellite of the latest modifications provides customers with thousands of high-quality communication channels for the simultaneous transmission of telephone, television, fax signals and digital data.

Heat treatment of food products.

Microwave radiation is used for heat treatment of food products at home and in the food industry. The energy generated by high-power vacuum tubes can be concentrated into a small volume for highly efficient thermal processing of products in the so-called. microwave or microwave ovens, characterized by cleanliness, noiselessness and compactness. Such devices are used in aircraft galleys, railway dining cars and vending machines, where quick food preparation and cooking are required. The industry also produces microwave ovens for household use.

Scientific research.

Microwave radiation has played an important role in studies of the electronic properties of solids. When such a body finds itself in a magnetic field, the free electrons in it begin to rotate around magnetic field lines in a plane perpendicular to the direction of the magnetic field. The rotation frequency, called the cyclotron frequency, is directly proportional to the magnetic field strength and inversely proportional to the effective mass of the electron. (The effective mass determines the acceleration of an electron under the influence of some force in the crystal. It differs from the mass of a free electron, which determines the acceleration of the electron under the influence of some force in a vacuum. The difference is due to the presence of attractive and repulsive forces that act on the electron in the crystal surrounding atoms and other electrons.) If microwave radiation falls on a solid body located in a magnetic field, then this radiation is strongly absorbed when its frequency is equal to the cyclotron frequency of the electron. This phenomenon is called cyclotron resonance; it allows one to measure the effective mass of an electron. Such measurements have provided much valuable information about the electronic properties of semiconductors, metals, and metalloids.

Microwave radiation also plays an important role in space research. Astronomers have learned a lot about our Galaxy by studying the 21 cm wavelength emitted by hydrogen gas in interstellar space. It is now possible to measure the speed and direction of movement of the galaxy's arms, as well as the location and density of regions of hydrogen gas in space.

SOURCES OF MICROWAVE RADIATION

Rapid progress in the field of microwave technology is largely associated with the invention of special vacuum devices - magnetron and klystron, capable of generating large amounts of microwave energy. A generator based on a conventional vacuum triode, used at low frequencies, turns out to be very ineffective in the microwave range.

The two main disadvantages of the triode as a microwave generator are the finite time of flight of the electron and the interelectrode capacitance. The first is due to the fact that it takes an electron some (albeit short) time to fly between the electrodes of a vacuum tube. During this time, the microwave field manages to change its direction to the opposite direction, so that the electron is forced to turn back before reaching the other electrode. As a result, electrons oscillate inside the lamp without any benefit, without giving up their energy to the oscillatory circuit of the external circuit.

Magnetron.

The magnetron, invented in Great Britain before World War II, does not have these disadvantages, since it is based on a completely different approach to the generation of microwave radiation - the principle of a volumetric resonator. Just as an organ pipe of a given size has its own acoustic resonance frequencies, a cavity resonator has its own electromagnetic resonances. The walls of the resonator act as inductance, and the space between them acts as the capacitance of a certain resonant circuit. Thus, a cavity resonator is similar to a parallel resonant circuit of a low-frequency oscillator with a separate capacitor and inductor. The dimensions of the cavity resonator are chosen, of course, so that the desired resonant ultra-high frequency corresponds to a given combination of capacitance and inductance.

The magnetron (Fig. 1) has several volumetric resonators located symmetrically around the cathode located in the center. The device is placed between the poles of a strong magnet. In this case, the electrons emitted by the cathode are forced to move along circular trajectories under the influence of a magnetic field. Their speed is such that at a strictly defined time they cross the open grooves of the resonators at the periphery. At the same time, they give off their kinetic energy, exciting vibrations in the resonators. The electrons are then returned to the cathode and the process repeats. Thanks to this device, the time of flight and interelectrode capacitances do not interfere with the generation of microwave energy.

Magnetrons can be made large, and then they produce powerful pulses of microwave energy. But the magnetron has its drawbacks. For example, resonators for very high frequencies become so small that they are difficult to manufacture, and such a magnetron itself, due to its small size, cannot be powerful enough. In addition, a magnetron requires a heavy magnet, and the required magnet mass increases with increasing power of the device. Therefore, powerful magnetrons are not suitable for aircraft on-board installations.

Klystron.

This electrovacuum device, based on a slightly different principle, does not require an external magnetic field. In a klystron (Fig. 2), electrons move in a straight line from the cathode to the reflective plate, and then back. In doing so, they cross the open gap of the donut-shaped cavity resonator. The control grid and resonator grids group electrons into separate “clumps” so that electrons cross the resonator gap only at certain times. The gaps between the bunches are matched to the resonant frequency of the resonator in such a way that the kinetic energy of the electrons is transferred to the resonator, as a result of which powerful electromagnetic oscillations are established in it. This process can be compared to the rhythmic swinging of an initially motionless swing.

The first klystrons were rather low-power devices, but later they broke all records of magnetrons as high-power microwave generators. Klystrons were created that delivered up to 10 million watts of power per pulse and up to 100 thousand watts in continuous mode. The klystron system of the research linear particle accelerator produces 50 million watts of microwave power per pulse.

Klystrons can operate at frequencies up to 120 billion hertz; however, their output power, as a rule, does not exceed one watt. Design options for a klystron designed for high output powers in the millimeter range are being developed.

Klystrons can also serve as amplifiers for microwave signals. To do this, you need to apply an input signal to the grids of the cavity resonator, and then the density of the electron bunches will change in accordance with this signal.

Traveling wave lamp (TWT).

Another electrovacuum device for generating and amplifying electromagnetic waves in the microwave range is a traveling wave lamp. It consists of a thin evacuated tube inserted into a focusing magnetic coil. There is a retarding wire coil inside the tube. An electron beam passes along the axis of the spiral, and a wave of the amplified signal runs along the spiral itself. The diameter, length and pitch of the spiral, as well as the speed of the electrons, are selected in such a way that the electrons give up part of their kinetic energy to the traveling wave.

Radio waves travel at the speed of light, while the speed of electrons in the beam is much slower. However, since the microwave signal is forced to travel in a spiral, its speed along the tube axis is close to the speed of the electron beam. Therefore, the traveling wave interacts with electrons for a long time and is amplified, absorbing their energy.

If no external signal is applied to the lamp, then random electrical noise at a certain resonant frequency is amplified and the traveling wave TWT operates as a microwave generator rather than an amplifier.

The output power of a TWT is significantly less than that of magnetrons and klystrons at the same frequency. However, TWTs can be tuned over an unusually wide frequency range and can serve as very sensitive low-noise amplifiers. This combination of properties makes the TWT a very valuable device in microwave technology.

Flat vacuum triodes.

Although klystrons and magnetrons are preferred as microwave oscillators, improvements have somewhat restored the important role of vacuum triodes, especially as amplifiers at frequencies up to 3 billion hertz.

Difficulties associated with time of flight are eliminated thanks to the very short distances between the electrodes. Unwanted interelectrode capacitance is minimized because the electrodes are mesh and all external connections are made on large rings located outside the lamp. As is customary in microwave technology, a volumetric resonator is used. The resonator tightly encloses the lamp, and ring connectors provide contact along the entire circumference of the resonator.

Gunn diode generator.

Such a semiconductor microwave generator was proposed in 1963 by J. Gunn, an employee of the Watson Research Center of the IBM Corporation. Currently, such devices provide power of only the order of milliwatts at frequencies of no more than 24 billion hertz. But within these limits it has undoubted advantages over low-power klystrons.

Since the Gunn diode is a single crystal of gallium arsenide, it is in principle more stable and durable than a klystron, which must have a heated cathode to create a flow of electrons and requires a high vacuum. In addition, a Gunn diode operates at a relatively low supply voltage, whereas powering a klystron requires bulky and expensive power supplies with voltages ranging from 1000 to 5000 V.

CIRCUIT COMPONENTS

Coaxial cables and waveguides.

To transmit electromagnetic waves in the microwave range not through the ether, but through metal conductors, special methods and specially shaped conductors are needed. Conventional wires that carry electricity, suitable for transmitting low-frequency radio signals, are ineffective at ultra-high frequencies.

Any piece of wire has capacitance and inductance. These so-called distributed parameters are becoming very important in microwave technology. The combination of the conductor's capacitance with its own inductance at ultra-high frequencies plays the role of a resonant circuit, almost completely blocking transmission. Since it is impossible to eliminate the influence of distributed parameters in wired transmission lines, we have to turn to other principles for transmitting microwave waves. These principles are embodied in coaxial cables and waveguides.

A coaxial cable consists of an inner conductor and a cylindrical outer conductor surrounding it. The gap between them is filled with a plastic dielectric, such as Teflon or polyethylene. At first glance, this may seem similar to a pair of ordinary wires, but at ultra-high frequencies their function is different. A microwave signal introduced from one end of the cable actually propagates not through the metal of the conductors, but through the gap between them filled with insulating material.

Coaxial cables are good at transmitting microwave signals up to several billion hertz, but at higher frequencies their efficiency decreases and they are unsuitable for transmitting high powers.

Conventional channels for transmitting microwave waves are in the form of waveguides. A waveguide is a carefully machined metal tube with a rectangular or circular cross-section, inside which a microwave signal propagates. Simply put, the waveguide directs the wave, causing it to be reflected from the walls every now and then. But in fact, the propagation of a wave along a waveguide is the propagation of oscillations of the electric and magnetic fields of the wave, as in free space. Such propagation in a waveguide is possible only if its dimensions are in a certain relationship with the frequency of the transmitted signal. Therefore, the waveguide is precisely calculated, processed precisely and intended only for a narrow frequency range. It transmits other frequencies poorly or not at all. A typical distribution of electric and magnetic fields inside a waveguide is shown in Fig. 3.

The higher the frequency of the wave, the smaller the dimensions of the corresponding rectangular waveguide; in the end, these dimensions turn out to be so small that its manufacture becomes excessively complicated and the maximum power transmitted by it is reduced. Therefore, the development of circular waveguides (circular cross-section) has begun, which can be quite large in size even at high frequencies in the microwave range. The use of a circular waveguide is hampered by some difficulties. For example, such a waveguide must be straight, otherwise its efficiency is reduced. Rectangular waveguides are easy to bend; they can be given the desired curvilinear shape, and this does not affect signal propagation in any way. Radar and other microwave installations usually look like intricate labyrinths of waveguide paths connecting different components and transmitting the signal from one device to another within the system.

Solid state components.

Solid-state components, such as semiconductors and ferrites, play an important role in microwave technology. Thus, germanium and silicon diodes are used to detect, switch, rectify, frequency convert and amplify microwave signals.

For amplification, special diodes are also used - varicaps (with controlled capacitance) - in a circuit called a parametric amplifier. Widespread amplifiers of this kind are used to amplify extremely small signals, since they introduce almost no noise or distortion of their own.

A ruby maser is also a solid-state microwave amplifier with a low noise level. Such a maser, whose operation is based on quantum mechanical principles, amplifies the microwave signal due to transitions between the internal energy levels of atoms in a ruby crystal. The ruby (or other suitable maser material) is immersed in liquid helium so that the amplifier operates at extremely low temperatures (only a few degrees above absolute zero). Therefore, the thermal noise level in the circuit is very low, making the maser suitable for radio astronomy, ultra-sensitive radar and other measurements where extremely weak microwave signals need to be detected and amplified.

Ferrite materials such as magnesium iron oxide and yttrium iron garnet are widely used for the manufacture of microwave switches, filters and circulators. Ferrite devices are controlled by magnetic fields, and a weak magnetic field is sufficient to control the flow of a powerful microwave signal. Ferrite switches have the advantage over mechanical ones that they have no moving parts subject to wear, and switching is very fast. In Fig. Figure 4 shows a typical ferrite device - a circulator. Acting like a traffic circle, the circulator ensures that the signal travels only along certain paths connecting various components. Circulators and other ferrite switching devices are used when connecting multiple components of a microwave system to the same antenna. In Fig. 4, the circulator does not allow the transmitted signal to pass to the receiver, and the received signal to the transmitter.

The tunnel diode, a relatively new semiconductor device operating at frequencies up to 10 billion hertz, is also used in microwave technology. It is used in oscillators, amplifiers, frequency converters and switches. Its operating power is low, but it is the first semiconductor device capable of operating efficiently at such high frequencies.

Antennas.

Microwave antennas come in a wide variety of unusual shapes. The size of the antenna is approximately proportional to the wavelength of the signal, and therefore designs that would be too bulky at lower frequencies are quite acceptable for the microwave range.

The designs of many antennas take into account those properties of microwave radiation that bring it closer to light. Typical examples include horn antennas, parabolic reflectors, metallic and dielectric lenses. Helical and spiral antennas are also used, often manufactured in the form of printed circuits.

Groups of slot waveguides can be arranged to produce the desired radiation pattern for the radiated energy. Dipoles like the well-known television antennas installed on roofs are also often used. Such antennas often have identical elements located at intervals equal to the wavelength, which increase directivity due to interference.

Microwave antennas are typically designed to be extremely directional because in many microwave systems it is important that energy is transmitted and received in a precisely defined direction. The directivity of the antenna increases with increasing its diameter. But you can make the antenna smaller while maintaining its directivity if you move to higher operating frequencies.

Many "mirror" antennas with a parabolic or spherical metal reflector are designed specifically to receive extremely weak signals coming, for example, from interplanetary spacecraft or from distant galaxies. In Arecibo (Puerto Rico) there is one of the largest radio telescopes with a metal reflector in the form of a spherical segment, the diameter of which is 300 m. The antenna has a fixed (“meridian”) base; its receiving radio beam moves across the sky due to the rotation of the Earth. The largest (76 m) fully movable antenna is located in Jodrell Bank (UK).

New in the field of antennas - an antenna with electronic directivity control; such an antenna does not need to be mechanically rotated. It consists of numerous elements - vibrators, which can be electronically connected to each other in different ways and thereby ensure the sensitivity of the “antenna array” in any desired direction.