What frequency is the microwave work

What will happen if you put your head in the microwave, how it affects Wi-Fi and other facts about the microwave

The simplest and most banal thing in the house is microwave! So it may seem at first glance, because what could be easier than put a plate with food in it, press a button and get a warm dish. That’s just not everyone guesses how this thing works and why it has become what we are used to seeing. The technology itself has existed for a very long time. But in our homes, these devices appeared relatively recently. By and large, this is just a box in which something like Wi-Fi works, only very powerful. Let’s figure out how it all works, on which the principle of operation of the device is based on, why it can be dangerous and how to use it. And at the same time we will find out why products sometimes explode in it, why the plate does not heat up and because of which home Wi-Fi network does not work near the microwave. By the way, you knew that it is more correct to call her microwave? Many have forgotten this reduction, but it is it that best reflects the principle of operation of the device.

The microwave is no doubt a real good. But not many people know everything about her.

The device of the microwave

The heart of the microwave oven is a magnetron: “An electronic device that generates microwaves when interacting the flow of electrons with an electric component of the ultra.frequency field in space, where the constant magnetic field perpendicular to the constant electric field”, as Wikipedia informs us.

What does it mean in practice? Microwaves are electromagnetic radiation of ultra.high frequency, which transfers their energy to molecules, thereby forcing them to move faster (that is, increasing the temperature). The electric component of electromagnetic waves accelerates the movement of molecules with the dipole moment, and since the most common in food products are the dipole molecules are water molecules, the microwave radiation mainly heats the water in any product-and everything else is heated from the water.

Having sorted out the principles of the microwave, it becomes easy to understand that no additional “harm”, which can cause food, heated or prepared in a microwave, of course, can not go. The only effect that microwaves have on food is the usual heating.

I must say that when starting to prepare this material, we were unpleasantly surprised, having discovered that discussions about the dangers of microwaves, it turns out, belong to the category of very tenacious “grandmother’s fairy tales”, and they can still be found on numerous (usually local) forums and discussions of the principles of “healthy diet”.

Electric circuit

All household models of the microwave oven are made according to the same scheme, and the main blocks are located in regular places. The technique of past generations differs only only by the execution of the control intensity. Modern devices are equipped with an electronic unit, and the power transformer is replaced by a more effective inverter.

How the protection system works

It is also worth covering in detail the functioning of security systems. They are divided into two significant groups.

• Parameters control of the hardware. This is a magnetron temperature sensor, fuses, cooling fans. They solve the problem of blocking potentially emergency situations and maintaining normalized indicators of electronics work
• Protecting a person from electricity lesion and microwave radiation.

Everyone who at least once disassembled the body of his microwave has encountered the protection systems against electric current protection systems. Microopaulists are placed at the key points of installation. Having removed the lid, the stove can no longer be turned on. This simply will not allow the protection system.

But more interesting is the neutralization scheme of microwaves. It should be understood that radiation even theoretically cannot be localized inside the furnace camera. Waves are reflected, including from products. Therefore, glass with a thin metal grill applied to it is installed on the front door. This is an antenna module. It is connected to a discharge that gives the accumulated energy in shots to the main power networks of the device.

Important! Microwave generates wiring interference. In some houses, this can be fixed for the work of other devices (in particular, Wi-Fi routers), especially if an openly cheap furnace with a poor noise-given agent is operated.

Microwave oven: history, device and principle of operation, performance regulation, aspects of safe use

Percy Spencer was 50 years old when he worked as an engineer in the American military-industrial company Raytheon (Divine Ray), who was actively engaged in the production of equipment for radars.

It was 1945 in the courtyard, it was then that Percy accidentally discovered a phenomenon that would be the basis of the first microwave oven: during the next experiment with a magnetron, a piece of chocolate in Spencer’s suddenly began to melt for no apparent reason.

Magnetron. This is a device that releases electromagnetic energy in the form of microwaves. Originally used for radar technology.

It turned out that ultra.frequency (microwave) radiation can effectively heat food products. Already on October 8, 1945, Percy Spencer was issued a patent on the world’s first microwave world designed to quickly defrost products.

In 1947, it was built (it was already possible to say that it left the assembly line) the first thawing microwave oven under the brand “Radarange”. It was an installation the size of a large modern refrigerator, which weighed 340 kg at a power of 3 kW.

The first mass supplies of the RADARANGE microwave oven to defrost food were directed to the dining rooms of military hospitals and to the US soldier’s dining rooms. Since 1949, serial production of these furnaces has already begun, so anyone who could afford such a purchase had the opportunity to purchase a microwave for defrosting for only 3,000.

The origin of the idea regarding the production of household microwaves for warming up food dates from October 25, 1955, when the first microwave work for home use was represented by the American company Tappan Company. The serial production of home microwaves began in 1962 by the Japanese company “Sharp”, but the demand for such an exotic household product was not high.

In the USSR, microwaves ZIL, Electronics and Maria MV began to be released in the 80s. In 1990, the microwave oven “Dnepryank-1” was released with a volume of 32 liters with a capacity of 1.3 kW at the power of microwave radiation 600 W, on the M-105-1 magnetron.

Thus began the mass production of home microwaves, allowing to quickly defrost food, warm it up, and even cook. Main condition. so that the product placed in a microwave contains water.

The principle of action and the device of the microwave

The bottom line is that the electromagnetic radiation of the decimeter range leads to the acceleration of the movement of the polar molecules of the dielectric (water) with a certain dipole moment.

Since the molecules are accelerated, their interaction under the influence of microwave radiation occurs, that is, the substance absorbs electromagnetic radiation, while the temperature of this substance increases.

The optimal dielectric absorption of electromagnetic radiation with water occurs at a frequency of 2.45 GHz, it is at this frequency that the magnetons of modern microwaves operate.

When compared with ordinary ovens, then in the microwave oven it is heated by food not only on the surface, but also in terms of product volume, since the electromagnetic wave penetrates the warm.up body to a depth of 1.5 to 2.5 cm, which accelerates the warming up, gives the average an increase in food temperature is 0.4 ° C per second.

To obtain microwave radiation with a given wavelength, a magnetron with specially designed structural parameters is used in the microwave. The radiation generated by the magnetron is transmitted through the waveguide and concentrated in the chamber in which the heated dish is placed.

The camera is closed with a metal door that prevents the spread of microwave waves beyond its limits. The power of magnetron is traditionally carried out from the secondary winding of the high.voltage transformer (MOT) with an output voltage of 2000 volts, which increases the doubling circuit (consisting of a capacitor and diode). The intensity of the magnetron cathode provides a special secondary winding with a voltage of 4 volts from the same transformer.

The classic way of automatically adjusting the thermal performance of the microwave oven is the same as it is used in iron and in household heating devices: the magnetron is periodically turned on and off so that the average thermal power supplied to the chamber in the form of electromagnetic waves would turn out to be equal to the set user.

Aspects of the safe use of microwave ovens

According to scientific data, the direct effect of microwave waves on the human body gives rise to a tangible thermal effect, and in the case of a long (or powerful) effect, it can lead to local overheating and cause serious burns.

So, at the density of microwave power in the region of 35 MW/sq.see a person feels heating. Prolonged exposure at a power density of more than 100 MW/kV.see cataracts and can lead to temporary infertility.

CHF density level of 10 MW/sq.See is considered safe. In relation to microwave stoves, according to the European standard, at a distance of 5 cm from the microwave oven, the maximum level of power density should not exceed 1 MW/sq.cm, but at a distance of 50 cm from the furnace. should not be more than 0.01 MW/sq.cm. It is these standards that comply with modern microwave ovens at the time of their manufacture.

By the way, the open furnace door always blocks its inclusion, that is, the microwave should never work with the open door.

Why in the process of preparation the container with the product should rotate?

It is difficult to construct the microwave in which the intensity of the microwaves would be exactly the same in the entire internal space of the furnace. in this case, food from all sides could be heated evenly. over, any product in the furnace absorbs microwaves, which also does not contribute to the same heating power, which (theoretically) could arise there.

The solution to the problem is that the container with food is constantly rotated, since this compensates for the uneven effects of the microwaves. For this, in most modern microwaves there is an automatically rotating stand. And the instructions for defrosting products remind us of the need to turn the heated product when about half of the due time passes.

Action and principle of work

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

The main condition necessary for the work of the microwave is the presence of the so.called polar molecules in the object. It is on them that the electromagnetic field of the device affects them. Fortunately, in almost all food products (with the exception of, unless, completely dehydrated), there is 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 of the magnetic field. In the process of rotation, these molecules literally rub against each other, and what is happening. Everyone knows. Try to quickly rub your palms one about the other. you feel warm?

Thanks to the variable electromagnetic field, the polar water molecules begin to rotate quickly.

The main difference between the effects of microwave radiation on the object from 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 the 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 depth of penetration depends on the frequency of radiation. And for standard microwave ovens operating at frequency 2.4 GHz, 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 from the inside and outside. over, he will do this in the shortest 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 the microwave of heating and the classic:

• High heating speed. Since the processing of high.frequency (HF) field is carried out simultaneously throughout the volume, the product is heated extremely quickly. in a matter of minutes.
• Uniform heating. Thanks to uniform heating, there is no need to heat its outer layer to elevated temperature. This excludes burning.
• The possibility of automation of cooking. When using a microwave oven, there is no need to monitor the process. to interfere, turn over, etc. It is enough to indicate the weight and type of the laid product and describe the necessary operation: heating, cooking, etc. The rest will do everything else on its own.
• The impossibility of roasting. The microwave field, unlike a pan or grill, warms the products evenly, which means that they are not able to fry them to a crispy crust.

The only drawback inherent in microwaves is the impossibility of frying, but the designers also decided this issue by equipping the device with conventional thermoelectric heaters, as in electric artists. With their help, you can easily fry the product. In addition, there are so.called circles made of special material, which is safely warmed up by microwave currents. Put the chop on such a plate and the stove will not only cook it quickly, but also fry it, because this pallet is heated up to 200 degrees.

The electrical circuit of the microwave.

Let’s take a look at the simplified electrical circuit of an ordinary microwave (click for increased).

As you can see, the scheme consists of the control part and the executive. The control unit, as a rule, consists of a microcontroller, display, a button or touch panel, an electromagnetic relay, a buzzer. These are the “brains” of the microwave. The scheme is shown by a separate board with the inscription Power and Control Curcuit Board. To power the control part of the microwave, a small reduction transformer is used. In the diagram, it is marked as l.V.Transformer (only the primary winding is shown).

Microcontroller through buffer elements (transistors) controls the electromagnetic relay: Relay1, Relay2, Relay3. They turn on/off the executive elements of the microwave oven in accordance with the specified algorithm.

Executive elements and chains. This is Magnetron (Magnetron), the Moto-Drawer of the table t.T.Motor (Turntable Motor), cooling fan f.M (Fan Motor), Grill Heater, Backlight Lamp O.L (Oven Lamp).

We especially note the executive chain, which is the generator of microwave radiation.

This chain begins with a high.voltage transformer (H.V.Transformer). He is the healthiest in the microwave. Actually, this is not surprising, because through it you need to pump a power of 1500. 2000 watts (1.5. 2 kW) necessary for the magnetron. The output (useful) power of magnetron 500. 850 watts.

A variable voltage of the network 220V is brought to the primary winding of the transformer. A variable voltage of the intensity 3.15V is removed from one of the secondary windings. It is brought to the glossy winding of the magnetron. Nepal winding is necessary for generating (emission) of electrons. It is worth noting that the current consumed by this winding can reach 10A.

Another secondary winding of a high.voltage transformer, as well as a doubling circuit at a high.voltage capacitor (H.V.Capacitor) and diode (H.V. Dior) creates a constant voltage of 4KV to power the magnetron anode. The current of the anode is small and is somewhere around 300 mA (0.3a).

As a result, electrons emitted by a tender winding begin their movement in vacuum.

A special trajectory of electron movement inside the magnetron creates a microwave radiation, which we need to heat food. The microwave radiation is discharged from the magnetron using the antenna and enters the camera through a segment of a rectangular wave of.

Here is such a simple but very sophisticated scheme is a kind of microwave warmer. Do not forget that the SCHF camera itself is an element of this microwave heater, as it represents, in fact, a resonator in which electromagnetic radiation occurs.

In addition to these elements, there are many protective elements in the microwave diagram (see. KSD heat switches and analogues.). So, for example, the thermal switch controls the temperature of the magnetron. Its full-time temperature during operation is about 80 °-100 ° C. This thermal switch is attached to the magnetron. By default, it is not shown in a simplified scheme.

Other protective thermal switches are signed in the diagram as Oven Thermal Cut-out (installed on the air duct), Grill Thermal Cut-out (controls the grill temperature).

In the presence of an abnormal situation and overheating of the magnetron, the thermal switch open the chain, and the magnetron stops working. In this case, the thermal switch is selected with a small margin. on the shutdown temperature 120. 145 ° C.

The very important elements of the microwave oven are three switches, which are built into the right end of the microwave camera chamber. When the front door is closed, the two switches close their contacts (Primary Switch. the main switch, Secondary Switch. secondary switch). The third. Monitor Switch (control switch). open its contacts when closing the door.

The malfunction of at least one of these circuit breakers leads to the inoperability of the microwave and the operation of the fuse (Fuse).

To reduce the interference that enters the power supply with a working microwave oven, there is a network filter. Noise Filter.

Harm.radiation harm

In the documents for any electronic device that is able to radiate microwave waves mentioned the so-called SAR. SAR is a specific coefficient of absorption of electromagnetic energy. In simple language. this is the power of radiation, which is absorbed by the living tissues of the body. SAR is measured in watts per kilogram. So, for the United States, the permissible level of 1.6 W/kg is determined. For Europe it is a little more. For the head of 2 W/kg, for other parts of the body and completely 4 W/kg. stringent restrictions operate in Russia, and the permissible radiation is measured already in WT/cm 2. The norm is 10 μW/cm 2.

Despite the fact that the microwave of radiation is considered non.ionizing, it is worth noting that in any case it affects any living organisms. For example, in the book “Brain in electromagnetic fields” (Yu. BUT. Colds) the results of many experiments are given, as well as the thorny history of the introduction of norms for irradiation by electromagnetic fields. The results are very curious. Microwave radiation affects many processes that occur in living organisms. If interesting, read.

Of all this, several simple rules follows. As little as possible to chat on a mobile phone. Keep it away from the head and important parts of the body. Do not sleep with a smartphone in an embrace. Use the headset if possible. Stay away from the base stations of cellular communications (we are talking about residential and working premises). It is no secret that mobile antennas are placed on the roofs of residential buildings.

It is also worth “throwing a stone into the garden” of mobile Internet when using a smartphone or tablet. If you are “sitting on the Internet”, then the device constantly transfers data from the base station. Even if the radiation in power is small (it all depends on the quality of the connection, interference and remoteness of the base station), then with prolonged use the negative effect is ensured. No, you will not bald and do not start to glow. There are no pain receptors in the brain. Therefore, he will eliminate the “problems” in the “form of strength and capabilities”. It will simply be more difficult to concentrate, fatigue will increase, and. It’s like drinking poison with small doses.