Microwave: action and principle of operation, microwave oven device and harm, at what frequency it works

Microwaves have entered our everyday life for a long time, but disputes about their usefulness and safety are still ongoing. It is curious that, when solving such issues on all kinds of forums and in personal meetings, the overwhelming majority does not even have an approximate idea of ​​the principle of the microwave oven.

That is why, before asking the question: is she your friend or enemy, it makes sense to find out what this an amazing machine that can boil a glass of water or cook a chicken without using a visible source heat. Almost everyone has seen a microwave oven in operation, but few have any idea how it does it.

Action and principle of operation

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

The main condition necessary for the operation of a microwave is the presence of so-called polar molecules in the object. It is on them that the electromagnetic field of the device affects. Fortunately, almost all food (except, perhaps, completely dehydrated) contains water, which consists of such molecules. Getting into a powerful alternating electromagnetic field, such molecules begin to rapidly change their position, following the constantly changing direction of the magnetic field. In the process of rotation, these molecules literally rub against each other, and everyone knows what happens during this. Try to quickly rub your palms together - do you feel warm?

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 from ordinary friction or heating 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 the object, but also penetrates deep into it, forcing the molecules to move and heat up.

The penetration depth depends on the radiation frequency. And for standard microwave ovens operating at 2.4 GHz, it is 1.5-2.5 cm. It is easy to guess that, for example, a pie placed in a microwave oven will warm up completely and evenly both inside and out. Moreover, he will do this in the shortest possible time, since the heating rate 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:

1. High warm-up speed. Since the treatment with a high-frequency (HF) field is carried out simultaneously throughout the entire volume, the product heats up extremely quickly - in a matter of minutes.
2. Uniform heating. Thanks to uniform heating, there is no need to heat its outer layer to an elevated temperature. This prevents burning.
3. Possibility of cooking automation. When using a microwave oven, there is no need to monitor the process - to stir, turn over, etc. It is enough to indicate the weight and type of the laid product and describe the required operation: heating, cooking, etc. The device will do the rest on its own.
4. Impossibility of roasting. The microwave field, unlike a frying pan or grill, heats food evenly, which means it is not able to fry them until crisp.

The only seemingly disadvantage inherent in microwaves is the impossibility of frying, but also the designers solved this issue by equipping the device with conventional thermoelectric heaters, as in electric ovens. With their help, you can easily fry the product. In addition, there are so-called Krusty plates, made of a special material that can be safely heated by microwave currents. Put 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 the microwave works. The heart of any such stove is a special generator that creates a high-frequency electromagnetic field of high intensity. It is called a magnetron. Further, the field created by him is directed to the product chamber with the help of 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. In addition, this is facilitated by the rotating tray, which is equipped with most microwave ovens.

The magnetron takes the most honorable place under the cover of the device.

The operation of the HF generator is controlled by an electronic unit assembled on a microprocessor. The firmware built into the block allows 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 a breakdown in insulation, whether the temperature inside the chamber has risen above the critical one, etc. The controller is controlled from panels of one type or another - push-button, touch-sensitive, etc. Well, of course, there is also a power supply in the oven, which provides energy to all the electronics and the magnetron itself.

This is what a microwave oven looks like in the diagram.

Dangers and harm of microwave

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

1. Radiation hazard.
2. Danger of electromagnetic radiation.
3. Poor influence of microwave on the quality of food.
4. The possibility of physical injury by the microwave field.
5. Increased risk of high voltage electric shock.

Radiation damage

According to this myth, everyone who is near the microwave oven receives radiation exposure. Moreover, even a switched-off stove radiates no worse than a Chernobyl tractor. But if you believe the basics of nuclear physics (everyone went through it in school), the radiation that everyone is so afraid of and which is really dangerous is ionizing radiation.

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

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

From 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 the induced radiation. The wavelength of the electromagnetic field of a microwave oven is 12 cm. It is much more logical to be afraid of the visible light emitted by Ilyich's lamp, the ionizing capacity of which is 3 orders of magnitude higher than the radiation of the microwave. But, despite the obvious, no one is afraid of light bulbs, microwave ovens - almost everyone.

Does high-frequency radiation alter the properties of products.

There is an opinion that, having been in the microwave, the products change their physical structure. Some connections are supposedly destroyed, others appear, the charge, pole, degree, memory change - whatever. After all this disgrace, wholesome food products turn into poison.

Microwave radiation, as mentioned above, affects polar molecules, which are water molecules. Today, science reliably knows that water is an amorphous body and has no structure at all, if it is not in a frozen state. How can this very structure change if an 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 kinds of pseudosciences such as homeopathy and "businessmen" selling "charging" water trays and other miracles of parallel technology worlds.

Electric shock

How electrical is the device.

Fears that a microwave oven is dangerous in terms of electric shock are, in principle, understandable. For the operation of the magnetron, a high voltage source is required - about 4 kV. If we add to this the power of a modern microwave oven, which can reach a kilowatt, then the whole horror of a person far from an electrician becomes understandable. Nevertheless, the same person quite calmly uses a 1.5-kilowatt vacuum cleaner and a two-kilowatt electric stove.

Remember the usual CRT TV, which served us for decades and continues to serve to this day. Accelerating anode voltage its kinescope reaches 30 kV. This is almost an order of magnitude higher than the voltage across the magnetron. If you open the microwave, then you can get under voltage. But in the TV, after all, the back cover is only four screws! Now think: do you have a lot of acquaintances who 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, microwave frequencies are harmful to humans. But a lot of modern devices operate at the same frequency: Wi-Fi modem, mobile phone, smartphone. Working with them is considered safe. Is microwave radiation harmful or harmless? Harmful, but only when a certain level is exceeded. Your cell phone is emitting, but its transmitter power is low. Although you keep it close to your temple, periodic phone calls will not cause much harm to your health. Another thing is a microwave oven. The power of its "transmitter" reaches a thousand watts.

But, firstly, unlike a mobile phone, the radiation of the magnetron is directed not in all directions, but into the working chamber. Secondly, and this is the main thing, the camera, like its door, has a special coating that prevents radiation from leaving the working area. Of course, the coating does not delay the microwave by 100%, but this is not necessary. You do not hold the microwave to your temple, like a telephone, and do not use it, burying your nose 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? We open medical documents that standardize the maximum permissible microwave radiation safe for humans and read: no more than 10 μW / cm2. Is it a lot or a little? It's time to look at the picture below:

Dependence of the field strength on the distance to the microwave oven.

At the very door of the microwave oven, 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 below the maximum allowable level by half. Thus, if you do not sit with the microwave on, literally in an embrace, and do not use it around the clock, then you need not fear for your health. But you can open the door? It is possible, only the magnetron will turn off immediately, since it has "foolproof" protection. The same protection will not allow you to stick your hand (and to some people the head) into a working device in order to check its serviceability "by touch."

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

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