Over the past decades, the technique of quickly heating food has quickly appeared in the arsenal of kitchen equipment of every family. It is also popular in offices and work cabins.
Marketers of microwave oven manufacturers are interested in mass sales of their products. They distribute advertisements among the population showing the advantages of their equipment over similar equipment operating on other principles. At the same time, the dangerous factors of microwaves are skillfully obscured by streamlined phrases or simply hushed up.
Let's try to impartially understand this confusing issue in order to draw useful conclusions for ourselves and safely, competently use our own technique.
What are the dangers of a microwave?
Its design is like a fabulous genie hidden in a bottle - a body from which dangerous energy can fly out in the event of an accidental breakdown or due to illiterate operation or repair.
According to the degree of impact on the human body, 3 different factors can be distinguished:
- exposure to microwave (microwave) radiation;
- the presence of a high-voltage electrical voltage from two to four kilovolts, necessary for the flow of direct current inside the magnetron;
- connecting a microwave to a 220 volt household home network.
Let's consider them in more detail.
high frequency radiation
It provides direct heating of food in a closed space of the body. The frequency of 2.45 GHz causes water molecules in food to resonate, which raises their temperature.
Where does the h / h radiation come from
The source of microwave microwave waves is a special device - a magnetron, which has:
- a cathode with a filament that provides a flow of electrons due to thermionic emission. The filament is heated by applying a voltage of 3 volts;
- copper anode with cooling plates and internal resonators;
- permanent magnets that create a deviating magnetic field;
- microwave radiation antenna.
Simplified, the microwave magnetron circuit can be represented by an electron tube, in the case of which electrons fly out of the cathode towards the anode, but fall into the cavities of the resonators that form high-frequency waves directed to the antenna.
This issue is explained in more detail by the owner of the video Sergey Bulavinov “How the magnetron works”.
How does the RF radiation scheme work?
The longer electromagnetic waves act on food, the more it heats up. At the same time, it is important to understand that during operation, the microwave rays of the magnetron affect only certain areas, creating separate hot spots.
To smooth out this drawback, a turntable is used in the microwave, constantly rotated by an electric motor. As a result, the food moves relative to the rays and warms up more evenly.
Radiation does not penetrate inside metals, but is reflected from their surface. It is a well-known fact that initially microwave devices were used only for military purposes in radars. Electromagnetic waves of this range propagate far in space, making it possible to track even high-speed low-flying aircraft.
At the same time, they are able to affect the components of electronic equipment, disrupt the operation of mobile phones, computers, televisions and any complex equipment encountered on their way.
If you place metal dishes or even a saucer with a beautiful golden rim inside the working chamber of the microwave oven, then all the energy of the magnetron will be concentrated on this metal surface, quickly heat it up, forming arc discharges and destroy the stove. Restoring her performance is unlikely to succeed.
This is explained by the fact that the operation of the microwave chamber occurs in the circuit of the resonant mode of the microwave path, which maximizes the power of heating food. It requires the obligatory presence of an internal source of energy absorption, without which self-destruction occurs. The manufacturer warns about this in his instructions.
The danger of microwave exposure to the human body
- A large dose of radiation, even with a short exposure, can create irreversible processes. It brings small volumes of water to a boil very quickly. Among the sad facts of statistics, there are cases when people lost their sight when rays hit the eyeball directly due to the fact that the liquid inside it almost instantly warmed up to a boiling point.
- Imperceptible at first irradiation of other parts of the human body also adversely affects health, causing dangerous damage to organs. The cumulative effect of the rays does not appear immediately, but over time, when genomes, leukemia or cancer of the skin areas are formed.
- People who use pacemakers while sitting near a microwave are at an increased risk.
An interesting fact is that in different countries the boundaries of the permissible influence of microwave rays on a person are not interpreted unambiguously. By American standards, the norm is adopted when an electromagnetic radiation flux density of 1 W * s / m2 is created. A person already feels such energy with his organs and must immediately leave the danger zone, because plasmolysis of cells quickly sets in. According to the standards of the USSR, this indicator has been reduced by a million times - to 1 μW * s / sq.m.
How is protection against RF radiation made?
The design of any microwave oven model consists of a housing, inside of which equipment is hidden from access by strangers, and controls are installed on the front panel.
Rectangular metal box on the front side is equipped with an opening door with transparent glass and mesh screen. It is suspended on two locks and fixed in the body with special latches with mustache limiters.
This is a mandatory part of the electromechanical interlock system that ensures the safety of the microwave oven.
The latches tightly press the closed door to the body, enter the slotted windows, equipped with special limit micro switches with changeover contacts. Their state corresponds to one of the positions: the space of the working cooking chamber is closed or open. The switching order of the contacts is set according to time.
Due to this design, during the operation of the magnetron, the internal volume of the case is created according to the Faraday cage principle, which excludes the exit of electromagnetic microwave radiation (SHF) from the case into the room with people and equipment.
The mode of operation of a microwave with an open door is to use it as a radar that irradiates a certain sector of space. Interlocking with micro switches prevents its creation.
If the operation of the locking devices is disrupted or the door hangers are unbalanced, then the microwave radiation of the microwave oven will penetrate through the cracks into the kitchen, creating a dangerous background.
How to check the door
Method number 1
There is a method available to each user. A strip 5–7 cm wide is cut off from a sheet of writing paper with a density of 90 ÷ 110. With the door open, it is alternately laid in different places:
- above, below the loops and between them;
- around the latches in the same way.
When the door is closed, a strip of paper should be held. If it is removed, then the hinge bolts inside the mounting holes need to be adjusted.
Method number 2
An ordinary mobile phone is placed in the working chamber, and the door is closed.
Attention!
Don't turn on the microwave!
The mobile phone periodically sends communication signals to the nearest receiving station to exchange service information with it at a frequency of 0.9÷1.9 GHz.
If the shielding is good, then it will disrupt the operation of this connection.
You can check this with a simple phone call.
The result will be one of the results:
- the phone is silent, and the station reports that the subscriber was not detected with proper microwave protection;
- creating a connection - if broken.
It is worth noting that both methods allow you to identify obvious defects. More accurate methods are based on measurements with special devices, which are not in the arsenal of the home master.
But there can be several channels for the passage of microwave radiation through the case, in addition to a loosely closed door. It “siphons” well through the smallest slots of the waveguide, penetrating through any conductors of electric current protruding outwards.
The magnetron antenna radiates microwave oscillations into the waveguide, which transmits them through the window into the working chamber to the products.
If there are design defects that were not detected during production or allowed during operation, then part of the high-frequency radiation will leave the housing with all the ensuing consequences.
This is a pretty good reason not to be closer than two meters from it when the microwave is working. It is especially relevant for young children, whose body is still developing.
It is impossible to find and eliminate the cause of microwave radiation at home without special equipment and training, and it is quite likely to worsen it with self-repair.
high voltage
To provide the magnetron with power, a transformer operates, which creates 2 kilovolts at the output. They come through a high-voltage capacitor, which accumulates a charge and a diode, which cuts off half of the harmonic, to the electrodes.
All these elements of the circuit are very dangerous, they can cause serious electrical injury if mishandled.
Disconnecting the power from the mains does not guarantee the absence of high-voltage voltage on the equipment. The capacitor stores it for a long time.
If you decide to disassemble the factory design, then at least follow the recommendations below.
The sequence of preparatory operations
Access to high voltage equipment is carried out in the following order:
- the microwave oven is disconnected from the mains by pulling out the plug from the power outlet;
- the time of 20 minutes is recorded, which is necessary for the discharge of the capacitance of high-voltage capacitors by standard resistors;
- after the end of the exposure, the ground wire is disconnected (often they are not used at all);
- wait 1 hour for the end of the discharge process.
When all four points are sequentially completed, you can remove the casing and look for a malfunction. Checking the absence of dangerous potentials will be useful. And it is generally unacceptable to apply voltage to the circuit for trial inclusions or checks.
Remember not only the danger of high voltage, but also microwave radiation from the magnetron, which is extremely dangerous without shielding with a protective housing.
Household voltage 220 volts
The microwave oven is designed to work safely on a three-wire network, made according to the TN-S grounding scheme. To connect it, you need to use everything.
In the power circuit of a microwave oven, a radio interference reduction filter is often used to smooth out possible voltage ripples issued to the network. For its effective operation, it is also necessary to take into account apartments. Otherwise, a dangerous potential of about 110 volts may form on the microwave housing.
This means that the minimum discomfort from the passage of an electric current through your body has already been prepared, and more sad incidents are not excluded.
Electrical diagram of a microwave oven
Let's consider it on the example of the Samsung RE2900 model. It allows you to understand the principle of operation, which is used in all models of any manufacturer and is distinguished by various specific modifications.
Explanatory notes are already made in the diagram in red.
Immediately on the left side, it can be seen that the grounding contact of the electrical plug is connected to the housing, which has a connection from the midpoint of the capacitor decoupling of the RF interference reduction filter.
A fuse FU1 is located at the power input of the circuit. Its condition must be checked by electrical methods - with a multimeter switched to ohmmeter mode.
The second available fuse, which can blow, protects the microwave from being used in emergency mode when the door microswitches are out of sequence.
In order for the magnetron circuit to start producing microwave radiation, it is necessary to open the health contact of the door microswitches and close all the others. Turning off any leads to the removal of the supply voltage from the high-voltage transformer.
The circuit includes two thermal fuses-sensors that open their position depending on the temperature of the monitored objects:
- housing of the magnetron on which it is installed;
- working chamber.
The first of them works periodically, protecting the magnetron from overheating, and the second - when the ventilation holes are clogged or the fan malfunctions. This is manifested by the premature shutdown of the microwave until the time set by the programmer.
The electric motors of the timer and the cooling fan are connected by a safety relay contact, the winding of which is disabled by blowing the Monitor fuse fuse.
The power control microswitch is located on the timer and removes voltage from the magnetron power circuit according to its algorithm.
Resistor R1 reduces the inrush current of the transformer by a few milliseconds due to the operation of the relay contact inrush relay. It limits the impulse caused by the discharge of the high-voltage capacitor when turned on until it acquires a charge. Due to this, the furnace smoothly enters the operating mode without pulse switching.
Such a power circuit of electrical connections, as you can see, is quite simple and reliable in operation. But the electronic components used by various manufacturers are distinguished by the variety of their designs and functionality. But, this is a topic for a completely different article.
We hope that we helped you understand how safe your microwave circuit works, and how to use it in the future - decide on your own, taking into account the information received.
The microwave oven has firmly entered into use and has become one of the indispensable attributes of any apartment. This household appliance allows you to heat up or cook food in a matter of minutes with the help of radiation invisible to the eye.
But in order to find out where this radiation comes from and how safe it is for humans, it is necessary to understand the device and principle of operation of the microwave oven magnetron, which is the generator of high-frequency waves.
Magnetron
What are microwaves and how do they heat food
Microwave is called electromagnetic radiation with a wavelength of 1 mm to 1 m. This type of radiation is used not only for domestic purposes, but also in navigation and radar systems, and also ensures the operation of cellular communications and satellite television.
Microwaves can be generated both artificially and naturally (for example, in the Sun). Another name for microwaves is microwave radiation, or SHF.
In all types of household microwaves, a single radiation frequency is set equal to 2450 MHz. This value is an international standard that household appliance manufacturers must strictly adhere to so that their products do not interfere with other microwave devices.
microwave radiation
The thermal effect of microwave radiation was discovered by the American physicist Percy Spencer in 1942. It was he who patented the use of a device that generates microwaves for cooking, thereby laying the foundation for the use of microwave ovens in everyday life.
In the next few decades, this technology was perfected, which made it possible to mass-produce simple and inexpensive devices for fast.
To heat any material in a microwave oven, it must contain dipole molecules, that is, molecules that have opposite electrical charges at both ends.
Water is the main source of food in food. Under the influence of microwave radiation, these molecules begin to line up along the lines of force of the electromagnetic field, changing their direction about 5 billion times per second. The friction that occurs between them is accompanied by the release of heat, which heats the food.
However, microwaves are not able to penetrate deeper than 2-3 cm from the surface of the product, so everything under this layer is warmed up due to heat conduction from heated areas.
Heating food with a microwave
The device of the magnetron and its application
In most types of microwave technology, a magnetron is a generator of microwave oscillations. Devices that are similar in their principle of operation - klystrons and platinotrons, are not so widespread. The magnetron was first used in microwave ovens in 1960. Most often in technology, a multicavity magnetron is used, consisting of several components:
- Anode. It is a copper cylinder divided into sectors with thick metal walls. These voluminous cavities are the resonators that create a ring system of oscillations. A voltage of about 4000 volts is applied to the anode.
- Cathode. It is located in the central part of the magnetron and is a cylinder, inside of which there is a filament. In this part of the device, electrons are emitted. A voltage of 3 volts is applied to the heater (filament).
- Ring magnets. Electromagnets or permanent magnets of high power, located in the end parts of the device, are necessary to create a magnetic field directed parallel to the axis of the magnetron. The movement of electrons is also carried out in this direction.
- Wire loop. It is connected to the cathode, fixed in the resonator and led to the emitter antenna. The loop serves to output microwave radiation into the waveguide, after which it enters directly into the microwave chamber.
Magnetron device
Due to the simplicity of design and low cost, magnetrons have found application in many areas, but they are most widely used:
- In microwave ovens. In addition to quick cooking and defrosting food in household ovens, magnetrons also allow you to perform production tasks. The industrial microwave oven can carry out heating, drying, melting, roasting and more. At the same time, it is important to remember that the microwave cannot be turned on empty, since in this case the radiation will not be absorbed by anything and will return back to the waveguide, which can lead to its breakdown.
- In radar. The radar antenna connected to the waveguide is actually a conical feed and is used in conjunction with a parabolic reflector (dish). The magnetron generates powerful short energy pulses with a short wavelength, part of which, being reflected, again enters the antenna and then to a sensitive receiver that processes the signal and displays it on the screen.
Magnetrons in radar
The principle of operation of the magnetron
The operation of a microwave oven is based on the conversion of electrical energy into ultra-high frequency electromagnetic radiation, which sets the water molecules in food in motion. Dipole molecules, constantly changing direction, generate heat, which allows you to quickly heat the products, while maintaining their beneficial properties. The device that generates microwaves is the magnetron.
The magnetron, in fact, is an electrovacuum diode, in which the phenomenon of thermionic emission is used. This phenomenon occurs in the process of heating the surface of the emitter or cathode. Under the influence of high temperature, the most active electrons tend to leave its surface, but this will only happen when voltage is applied to the anode. In this case, an electric field arises, and the electrons begin to move towards the anode, heading along its lines of force. If the electrons are in the zone of action of the magnetic field, then their trajectories deviate towards the direction of the lines of force.
Electrovacuum diode
The anode of the magnetron has the form of a cylinder with a system of cavities, or resonators, inside of which there is a cathode with an incandescent filament. Two ring magnets located at the edges of the anode create a magnetic field inside the anode, due to which the electrons do not move directly from the cathode to the anode, but change their trajectory, rotating around the cathode. Near the resonators, the electrons give them part of their energy, which leads to the formation of a powerful microwave field in their cavities, which is output to the outside using a wire loop connected to the emitter antenna.
To activate the magnetron, it is necessary to apply a high voltage of the order of 3-4 thousand volts to the anode. Therefore, the connection of the magnetron to the household electrical network is carried out by means of a high-voltage transformer. In addition, the microwave oven switching circuit includes a waveguide that transmits radiation into the chamber, a switching circuit, a control unit, as well as protection and cooling elements. In addition, the inner walls of the chamber and a thin metal mesh on the door of the device prevent radiation from escaping beyond its limits.
Magnetron switching circuit
How the magnetron affects microwave power
Most modern manufacturers of microwave ovens offer the ability to choose the power of the device. From this parameter, in turn, depends on the mode of operation (defrosting or heating) and the speed of heating food. However, the design features of the magnetron do not allow reducing its power, therefore, to reduce the intensity of heating, power is supplied to it at certain intervals. These pauses in the operation of the magnetron can be noticed if you turn on the microwave at medium power and listen to the sound of its operation.
Not so long ago, some manufacturers of household appliances announced the appearance of a number of models of microwave ovens with an inverter power circuit. The use of this scheme made it possible not only to increase the amount of usable space in the chamber by reducing the dimensions of the emitter, but also to reduce the power consumption of the device. Unlike conventional models, the heating temperature in inverter-type furnaces changes smoothly, but their cost is much higher.
Cooling and protection of the magnetron
During operation, the magnetron generates a large amount of heat, so a radiator is installed on its case. Since overheating is the main cause of magnetron failure, other methods are used to protect it:
- Thermal relay. This device is used to protect the magnetron, as well as the grill, if available in the model. The thermal fuse is equipped with a bimetal plate that can be adjusted to a specific temperature. If this value is exceeded, it bends and opens the power circuit.
- Fan. It not only blows cool air on the magnetron radiator, but also performs a number of other useful functions, such as cooling the electronic components of the device, circulating air inside the chamber during grill operation, and also removing hot steam to the outside through special holes.
- Locking system. Several microswitches control the position of the microwave oven door, preventing the magnetron from turning on when it is open.
Thermal relay
Is it possible to replace the magnetron
The main advantage of modern magnetrons for domestic microwave ovens is their interchangeability. Magnetrons manufactured by other companies will be suitable for various models of microwaves, so they can be changed if necessary. In this case, the only necessary requirement will be matching in power. You can buy a magnetron in many electronics stores, but in order to make the right choice, you need to understand its parameters and markings. Most often, the following models of magnetrons are installed in microwave ovens:
- 2M 213 (600 W rated power and 700 W under load);
- 2M 214 (1000 W);
- 2M 246 (1150 W - maximum power).
Even having studied all the necessary parameters of this device, it is not recommended to replace the magnetron at home. Firstly, it will be quite difficult to remove it yourself, and secondly, only a qualified specialist will be able to ensure its safe operation after installation.
Standard magnetron configuration
Diagnostics of malfunctions and their causes
Replacing the magnetron can require quite a significant financial outlay, so before buying a new device, it is necessary to diagnose the old one to make sure that it is really faulty. The test can be done at home with a conventional tester. This will require:
- Unplug the microwave from the mains.
- Remove the protective cover and carry out a visual inspection of the part.
- "Ring out" the main elements of the printed circuit board using a tester or "multimeter".
- Check the thermostat.
Diagnostics
At the end of the diagnosis, it is possible to draw conclusions about the malfunction of certain parts. The main reasons for the failure of the magnetron include the following:
- Vacuum tube cap failure. It can be replaced by yourself, simply by picking up a similar cap from another magnetron. The seats of such caps have a standard configuration.
- Heater break. If or incorrectly loaded, the magnetron will overheat, which can lead to excessive heating of the filament and its breakage. To diagnose it, it is necessary to measure the resistance between the legs of the capacitor. If its value is within 5-7 ohms, then the heater is working.
- Breakdown capacitor. If the tester does not show an “infinite” resistance value between its contacts, then the capacitor must be replaced.
Good afternoon, dear Khabrovites.
This post will be about the undocumented features of the microwave oven. I'll show you how many useful things can be done by using a slightly modified microwave in a non-standard way.
The microwave oven contains a high-powered microwave generator.
The power of the waves that are used in the microwave has been haunting my mind 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 generates as much radiation as 10,000 wi-fi routers, 5,000 mobile phones or 30 basic mobile towers! In order to prevent this power from escaping, a double steel protective screen is used in the microwave.I open the case
I want to warn you right away that microwave electromagnetic radiation can harm your health, and high voltage can cause death. But that won't stop me.Removing the lid from the microwave reveals a large transformer: MOT. It raises the mains voltage from 220 volts to 2000 volts to power the magnetron.
In this video, I want to show what such tension is capable of:
Antenna for magnetron
Having removed the magnetron from the microwave, I realized that it was impossible to turn it on just like that. The radiation will spread from it in all directions, hitting everything around. Without hesitation, I decided to make a directional antenna from a coffee can. Here is 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 turned on, I saw that the bulbs light up exactly where it is needed:
Unusual experiences
I want to note right away that microwaves have a much stronger effect on equipment than on people and animals. Even at a distance of 10 meters from the magnetron, the equipment gave severe failures: the TV and the music center made a terrible growling sound, the mobile phone first lost the network, and then completely hung up. 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 a mains capacitor exploded in it. In this video, I show the process of assembling the antenna and the effect of the magnetron on the technique:Plasma can be obtained using non-ionizing radiation of a magnetron. In an incandescent lamp, brought to the magnetron, a brightly glowing yellow ball, sometimes with a purple tint, is lit, like ball lightning. If the magnetron is not turned off in time, the light bulb will explode. Even an ordinary paper clip, under the influence of microwaves, turns into an antenna. An EMF of sufficient strength is induced on it to ignite the arc and melt this paper clip. Fluorescent and "housekeeper" lamps are lit at a sufficiently large distance and glow right in the hands without wires! And in a neon lamp, electromagnetic waves become visible:
I want to reassure you, my readers, none of my neighbors suffered from my experiments. All the nearest neighbors fled the city as soon as the hostilities began in Lugansk.
Safety
I strongly do not recommend repeating the experiments I have described because special precautions are required when working with microwaves. All experiments are performed solely for scientific and educational purposes. The harm of microwave radiation to humans is not yet fully understood. When I came close to the working magnetron, I felt warm, like from an oven. Only from the inside and, as it were, pointwise, in waves. I didn't feel any more harm. But still, I strongly do not recommend directing a working magnetron to people. Due to thermal exposure, protein in the eyes can coagulate and a blood clot can form. There is also controversy that such radiation can cause cancer and chronic diseases.Unusual applications of the magnetron
1 - Pest burner. Microwaves effectively kill pests, both in wooden buildings and on the tanning lawn. The bugs under the hard shell have a moisture-containing inside (what an abomination!). The waves turn it into steam in an instant, without harming the tree. I tried to kill pests on a living tree (aphids, codling moth), also effective, but it is important not to overdo it because the tree also heats up, but not so much.2 - Metal melting. The power of the magnetron 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 - Cleanup from wiretapping. If you treat a room with a magnetron, you can kill all unwanted electronics in it: hidden video cameras, electronic bugs, radio microphones, GPS tracking, hidden chips, and the like.
5 - Silencer. With the help of a magnetron, you can easily calm down even the noisiest neighbor! Microwave penetrates up to two walls and "calms" any sound technique.
These are not all possible applications tested by me. Experiments continue and soon I will write an even more unusual post. Still, I want to note that it is dangerous to use a microwave in this way! Therefore, it is better to do this in cases of emergency and subject to safety rules when working with microwaves.
That's all for me, be careful when working with high voltage and microwaves.
Properties of microwave waves
In modern life, microwaves are used very actively. Take a look at your cell phone - it operates in the microwave range.
All technologies such as Wi-Fi, wireless Wi-Max, 3G, 4G, LTE (Long Term Evolution), Bluetooth short range radio interface, radar and radio navigation systems use microwaves.
Microwaves have found application in industry and medicine. In another way, microwaves are also called microwaves. The operation of a household microwave oven is also based on the use of microwave radiation.
Microwave- these are the same radio waves, but the wavelength of such waves is from tens of centimeters to a millimeter. Microwaves occupy an intermediate position between ultrashort waves and infrared radiation. This intermediate position also affects the properties of microwaves. Microwave radiation has the properties of both radio waves and light waves. For example, microwave radiation has the qualities of visible light and infrared electromagnetic radiation.
LTE mobile network station
Microwaves, whose wavelength is centimeters, at high levels of radiation can have a biological effect. In addition, centimeter waves pass through buildings worse than decimeter waves.
Microwave radiation can be concentrated into a narrow beam. This property directly affects the design of receiving and transmitting antennas operating in the microwave range. No one will be surprised by the concave parabolic dish of satellite television, which receives a high-frequency signal, like a concave mirror that collects light rays.
Microwaves, like light, travel in a straight line and are obscured by solid objects, just as light does not pass through opaque bodies. So, if you deploy a local Wi-Fi network in an apartment, then in the direction where the radio wave encounters obstacles in its path, such as partitions or ceilings, the network signal will be less than in the direction more free from obstacles.
Pine forests weaken the radiation from GSM cellular base stations quite strongly, since the size and length of the needles are approximately equal to half the wavelength, and the needles serve as a kind of receiving antenna, thereby weakening the electromagnetic field. Dense tropical forests also affect the weakening of the signal of the stations. With increasing frequency, the attenuation of microwave radiation increases when it is blocked by natural obstacles.
Cellular communication equipment can be found even on power poles
Propagation of microwaves in free space, for example, along the surface of the earth is limited by the horizon, in contrast to long waves, which can bend around the globe due to reflection in the layers of the ionosphere.
This property of microwave radiation is used in cellular communications. The service area is divided into cells in which the base station operates at its own frequency. The neighboring base station is already operating at a different frequency so that nearby stations do not interfere with each other. Next comes the so-called reuse of radio frequencies.
Since the radiation of the station is blocked by the horizon, it is possible to install a station operating at the same frequency at some distance. As a result, such stations will not interfere with each other. It turns out that the radio frequency band used by the communication network is saved.
GSM base station antennas
RF spectrum is a natural, limited resource, like oil or gas. The distribution of frequencies in Russia is handled by the State Commission on Radio Frequencies - SCRF. To obtain permission to deploy wireless access networks, real "corporate wars" are sometimes waged between mobile network operators.
Why is microwave radiation used in radio communication systems if it does not have such a range of propagation as, for example, long waves?
The reason is that the higher the frequency of the radiation, the more information can be transmitted using it. For example, many people know that fiber optic cable has an extremely high information transfer rate, calculated in terabits per second.
All high-speed telecommunications backbones use optical fiber. Light is used here as a carrier of information, the frequency of the electromagnetic wave of which is incommensurably higher than that of microwaves. Microwaves, in turn, have the properties of radio waves and propagate freely in space. Light and laser beams are strongly scattered in the atmosphere and therefore cannot be used in mobile communication systems.
Many homes have a microwave oven in their kitchen, which is used to heat food. The operation of this device is based on the polarization effects of microwave radiation. It should be noted that the heating of objects with the help of microwave waves occurs to a greater extent from the inside, in contrast to infrared radiation, which heats the object from the outside to the inside. Therefore, you need to understand that heating in a conventional and microwave oven occurs in different ways. Also microwave radiation, for example, at a frequency 2.45 GHz capable of penetrating a few centimeters into the body, and the heat produced is felt at a power density of 20 – 50 mW / cm 2 exposed to radiation for a few seconds. It is clear that powerful microwave radiation can cause internal burns, since heating occurs from the inside.
At a microwave operating frequency of 2.45 GHz, ordinary water is capable of maximally absorb the energy of microwave waves and convert it into heat, which, in fact, happens in the microwave.
While there is an ongoing debate about the dangers of microwave radiation, the military already has the opportunity to test the so-called "ray gun" in practice. So in the United States, an installation has been developed that "shoots" with a narrowly directed microwave beam.
The installation looks like something like a parabolic antenna, only not concave, but flat. The diameter of the antenna is quite large - this is understandable, because it is necessary to concentrate the microwave radiation into a narrow beam over a long distance. The microwave gun operates at a frequency of 95 GHz, and its effective "shooting" range is about 1 kilometer. According to the creators, this is not the limit. The whole installation is based on an army hummer.
According to the developers, this device does not pose a deadly threat and will be used to disperse demonstrations. The power of the radiation is such that when a person enters the focus of the beam, he experiences a strong burning sensation of the skin. According to those who fell under such a beam, the skin seemed to be warmed up by very hot air. In this case, a natural desire arises to hide, to escape from such an effect.
The operation of this device is based on the fact that microwave radiation with a frequency of 95 GHz penetrates half a millimeter into the skin layer and causes local heating in a fraction of a second. This is enough for the person under the gun to feel pain and burning of the skin surface. A similar principle is used for heating food in a microwave oven, only in a microwave oven microwave radiation is absorbed by the food being heated and practically does not go beyond the chamber.
At the moment, the biological effects of microwave radiation are not fully understood. Therefore, no matter what the creators say that the microwave gun is not harmful to health, it can harm the organs and tissues of the human body.
It is worth noting that microwave radiation is most harmful to organs with slow heat circulation - these are the tissues of the brain and eyes. Brain tissues do not have pain receptors, and it will not be possible to feel the obvious effect of radiation. It is also hard to believe that a lot of money will be allocated for the development of a "demonstrator repeller" - $ 120 million. Naturally, this is a military development. In addition, there are no special obstacles to increase the power of the high-frequency radiation of the gun to a level where it can already be used as a damaging weapon. Also, if desired, it can be made more compact.
The military plans to create a flying version of the microwave gun. Surely it will be installed on some kind of drone and will be controlled remotely.
Harm of microwave radiation
In the documents for any electronic device that is capable of emitting microwave waves, the so-called SAR is mentioned. SAR is the Specific Absorption Rate for Electromagnetic Energy. In simple terms, this is the radiation power that is absorbed by the living tissues of the body. SAR is measured in watts per kilogram. So, for the United States, an acceptable level of 1.6 W / kg is defined. For Europe, it is a little more. For the head 2 W / kg, for the rest of the body and at all 4 W / kg. In Russia, more stringent restrictions apply, and permissible radiation is already measured in W / cm 2. The norm is 10 μW / cm 2.
Despite the fact that microwave radiation is considered to be non-ionizing, it is worth noting that in any case it affects any living organisms. For example, the book "The Brain in Electromagnetic Fields" (Yu. A. Kholodov) presents the results of many experiments, as well as the thorny history of introducing standards for exposure to electromagnetic fields. The results are very curious. Microwave radiation affects many processes occurring in living organisms. If interested, read.
From all this follows a few simple rules. Talk on your cell phone as little as possible. Keep it away from the head and important parts of the body. Do not sleep with a smartphone in an embrace. Use a headset if possible. Stay away from cellular base stations (we are talking about residential and work areas). It's no secret that mobile antennas are placed on the roofs of residential buildings.
It is also worth "throwing a stone in the garden" of the mobile Internet when using a smartphone or tablet. If you "sit on the Internet", then the device constantly transmits data to the base station. Even if the radiation power is small (it all depends on the quality of communication, interference and remoteness of the base station), then with prolonged use, a negative effect is provided. No, you won't go bald or glow. There are no pain receptors in the brain. Therefore, he will eliminate "problems" "to the best of his ability and ability." It will just be more difficult to concentrate, fatigue will increase, etc. It's like drinking poison in small doses.
14.08.2013 29.04.2016 by gotovlyu v mikrovolnovke
To understand how a microwave oven works, you will have to remember the basic course of school physics. But even those who do not remember this course very well, after a detailed explanation, they will know exactly the principle of the microwave oven and will be able to answer themselves and others about the dangers of the device itself or the food that is cooked in it.
The device is called a microwave oven not by chance. In it (and not only in it, for example, in cell phones, satellite television, and there are also natural waves that the Sun creates), microwave radiation is used or, as it is also called, microwave radiation, consisting of electromagnetic waves, the length of which is 1 millimeter - 1 meter.
In addition to length, waves are characterized by frequency. For microwaves, according to an international agreement, a frequency of 2450 MHz has been adopted (this frequency will not interfere with the operation of other devices with microwaves).
Electromagnetic speeds, if anyone did not know or forgot, I remind you, they propagate at a speed of 300,000 km per second. That's right, it's the speed of light. Knowing the microwave frequency of the oven, you can get the length. For this, the speed must be divided by the frequency, we get 12.25 cm. These are the waves that live in your microwave.
Another characteristic of the waves, so that the principle of operation of the microwave oven is clearly understood. A wave is a combination of two alternating fields (magnetic and electric). There are no magnetic properties in the products, so this field is not considered. But the electric field that the wave creates is the basis.
The principle of operation of the microwave oven
In order for microwaves to heat food, it must contain dipole (different charges at different ends, that is, one is positive, the other is negative) molecules. And, as it turns out, they are. These are molecules of sugar, fat, but most importantly, water, which is found in almost all products.
In each, even the smallest piece of the product, there is a huge amount of dipole molecules, which are located as they please, that is, randomly. But as soon as they fall under the influence of an electric field, the molecules are immediately built in even rows on the field lines of force, and in a strict order: plus - in one direction, minus - in the other. Lined up. But as soon as the field changes polarity, the molecules follow it, turning one hundred and eighty degrees. Now imagine that such a change in the field occurs very often. Or rather, with a frequency of 2450 MHz. Let me remind you that 1 hertz is 1 oscillation in 1 second, so it is easy to calculate that 1 MHz is 1 million oscillations in 1 second. For 1 oscillation, the field changes twice. You can calculate how many times our molecules have changed their position in a second. For those who believe in the word - 4900000000 times.
Have you imagined this frantic movement of molecules? And during this movement, the molecules come into contact with each other, releasing heat, which “warms” the product.
Knowing the principle of operation of the microwave oven will not be able to cook a lot of dishes in a hurry,
A little about the rules of use that will help you master the process of cooking in the microwave:
How to "teach" your recipes to the microwave. This
Delicious potatoes with meat in a pot,
For those to whom physics is sooooo far away, I suggest rubbing your palms together. Feel how warm they are. Here is the same principle. And by the way, this example shows that, in this way, that is, rubbing our hands intensively, we will not be able to heat the tissues too deeply. Similarly, microwaves cannot penetrate deeper than three centimeters. Therefore, thermal conductivity is connected to the action of microwaves, due to which the generated heat penetrates deeper than three centimeters.
What does this mean practically and how does it relate to cooking in the microwave? This means that you do not need to cook a large piece at maximum power. It is better to set the middle one and let the heat quietly penetrate deep into it, preparing the piece well and not charring the outer part.
And liquid foods need to be periodically mixed, helping heat penetrate into the middle of the dish.
Recently, there have been rumors that heating food in the microwave starts from the inside of the product, which leads to the loss of valuable trace elements in food. But this is an erroneous opinion, as you already understood. Do a practical experiment: heat a boiled, unpeeled potato, and then look at its dried-out, fried crust and tender core.
How a microwave oven works
The required products are placed inside the microwave oven on a rotating stand, thanks to which the heating occurs evenly. Microwaves are produced by a powerful electronic lamp - a magnetron. If your household appliance fails, do not rush to repair it yourself, keep in mind that a very high voltage is applied to the magnetron - do not risk yourself and your family.
Protects from radiation mesh on the door of the device.
The device package includes:
- power cord,
- energy converter;
- magnetron;
- guiding and distributing wave devices;
- capacitor;
- rectifier;
- door equipped with seals;
- oven chamber with a plate;
- fan.
