Among the huge variety of electromagnetic waves that exist in nature, microwave or microwave radiation (microwave) occupies a very modest place. This frequency range can be found between radio waves and the infrared part of the spectrum. Its length is not particularly great. These are waves with a length of 30 cm to 1 mm.

Let's talk about its origin, properties and role in the human environment, about how this “silent invisibility” affects the human body.

Microwave radiation sources

There are natural springs microwave radiation - Sun and others space objects. It was against the background of their radiation that the formation and development of human civilization took place.

But in our century, saturated with all kinds of technical achievements, man-made sources have also been added to the natural background:

• radar and radio navigation installations;
• satellite television systems;
• cell phones and microwave ovens.

How microwave radiation affects human health

The results of a study of the influence of microwave radiation on humans made it possible to establish that microwave rays do not have an ionizing effect. Ionized molecules are defective particles of matter that lead to mutation of chromosomes. As a result, living cells can acquire new (defective) characteristics. This finding does not mean that microwave radiation is not harmful to humans.

The study of the influence of microwave rays on humans has made it possible to establish the following picture - when they hit the irradiated surface, partial absorption of the incoming energy by human tissue occurs. As a result, high-frequency currents are excited in them, heating the body.

As a reaction of the thermoregulation mechanism, increased blood circulation follows. If the irradiation was local, rapid heat removal from heated areas is possible. With general radiation there is no such possibility, so it is more dangerous.

Since blood circulation acts as a cooling factor, the thermal effect is most pronounced in organs depleted of blood vessels. First of all, in the lens of the eye, causing its clouding and destruction. Unfortunately, these changes are irreversible.

The most significant absorption capacity is found in tissues with a high content of liquid components: blood, lymph, mucous membrane of the stomach, intestines, and the lens of the eye.

As a result, you may experience:

• changes in the blood and thyroid gland;
• decreased efficiency of adaptation and metabolic processes;
• changes in the mental sphere that can lead to depressive states, and in people with an unstable psyche - provoke suicidal tendencies.

Microwave radiation has a cumulative effect. If at first its influence is asymptomatic, then pathological conditions gradually begin to form. Initially, they manifest themselves in increased frequency of headaches, fatigue, sleep disturbances, increased blood pressure, heart pain.

With prolonged and regular exposure to microwave radiation, it leads to the profound changes listed earlier. That is, it can be argued that microwave radiation has negative impact on human health. Moreover, age-related sensitivity to microwaves was noted - young organisms turned out to be more susceptible to the influence of microwave EMF (electric magnetic field).

Means of protection against microwave radiation

The nature of the impact of microwave radiation on a person depends on the following factors:

• distance from the radiation source and its intensity;
• duration of irradiation;
• wavelength;
• type of radiation (continuous or pulsed);
• external conditions;
• state of the body.

For quantification danger, the concept of radiation density and permissible exposure rate was introduced. In our country, this standard is taken with a tenfold “safety margin” and is equal to 10 microwatts per centimeter (10 μW/cm). This means that the power of the microwave energy flow at a human workplace should not exceed 10 μW for each centimeter of surface.

How can this be? The obvious conclusion is that exposure to microwave rays should be avoided in every possible way. Reducing exposure to microwave radiation in the home is quite simple: you should limit the time of contact with household sources.

People whose professional activity associated with exposure to microwave radio waves. Means of protection against microwave radiation are divided into general and individual.

The flux of emitted energy decreases in inverse proportion to the increase in the square of the distance between the emitter and the irradiated surface. Therefore, the most important collective protective measure is to increase the distance to the radiation source.

Other effective measures to protect against microwave radiation are the following:

Most of them are based on the basic properties of microwave radiation - reflection and absorption by the substance of the irradiated surface. Therefore, protective screens are divided into reflective and absorbent.

Reflective screens are made of sheet metal, metal mesh and metallized fabric. The arsenal of protective screens is quite diverse. These are sheet screens made of homogeneous metal and multilayer packages, including layers of insulating and absorbing materials (shungite, carbon compounds), etc.

The final link in this chain is the means personal protection from microwave radiation. They include workwear made of metallized fabric (robes and aprons, gloves, capes with hoods and goggles built into them). The glasses are covered with a thin layer of metal that reflects radiation. They are required to be worn when exposed to radiation of 1 µW/cm.

Wearing protective clothing reduces the level of radiation exposure by 100–1000 times.

Benefits of microwave radiation

All previous information with a negative orientation is intended to warn our reader from the danger emanating from microwave radiation. However, among the specific effects of microwave rays, the term stimulation is found, that is, an improvement under their influence in the general condition of the body or the sensitivity of its organs. That is, the effect of microwave radiation on a person can be beneficial. The therapeutic property of microwave radiation is based on its biological effect in physiotherapy.

Radiation emanating from a specialized medical generator penetrates the human body to a given depth, causing tissue heating and a whole system of useful reactions. Sessions of microwave procedures have an analgesic and antipruritic effect.

They are successfully used to treat frontal sinusitis and sinusitis, trigeminal neuralgia.

To influence endocrine organs, respiratory organs, kidneys, and the treatment of gynecological diseases use microwave radiation with greater penetrating power.

Research into the effect of microwave radiation on the human body began several decades ago. The accumulated knowledge is sufficient to be confident that the natural background of these radiations is harmless to humans.

Various generators of these frequencies create an additional dose of impact. However, their share is very small, and the protection used is quite reliable. Therefore, phobias about their enormous harm are nothing more than a myth if all conditions of operation and protection from industrial and household sources microwave emitters.

The development of microwave technology in the last two decades has contributed to its introduction into physiotherapy practice. Microwaves have a number of physical properties that can be used to treat certain diseases (such as psoriasis, rheumatism and other autoimmune diseases). The properties of these waves are the following: a) their energy can be concentrated on individual parts of the body; b) they are reflected from dense surfaces; c) their frequency is close to the frequency of relaxation vibrations of water; d) they are more thermogenic than ultrashort waves.

Under the influence of microwaves, vibrations of ions and the dipole water molecules they contain occur in the tissues of a living organism.. Absorption of wave energy in tissues due to vibrations of ions is practically independent of frequency, while absorption due to vibrations of dipole water molecules increases with increasing frequency. However, this increase occurs up to a frequency specific for each body of molecules (the so-called relaxation frequency). With more high frequencies Due to inertia, the molecules no longer have time to react to too frequent changes in the wave fields, and therefore the absorption of wave energy decreases sharply. For water molecules, this limiting relaxation frequency is about 2-10 Hz (wavelength about 1.5 cm). Due to these features, as the wavelength shortens, the role of molecules in the overall absorption of wave energy in tissues increases. In the 10-centimeter wavelength range, approximately half is absorbed due to vibrations of water molecules. total energy, and in the 3-centimeter - already 98%. Since the body consists of more than half water, the significance of this fact for the action of microwaves is clear, especially for tissue with a high water content (blood, lymph, muscles, nervous system).

Microwaves have both thermal and extrathermal effects. For the first time, their extrathermal effect on humans was established by S. Ya. Turlygin, who observed the appearance of drowsiness after exposure to centimeter waves of very low intensity. This was later confirmed by numerous observations. When a person is systematically exposed to high-power microwaves on the face, clouding of the lens, functional changes in the nervous system, dysfunction of the visual and olfactory analyzers, etc. are observed, which has led to the need to establish in industry maximum permissible doses of exposure to humans during working hours - not more than 0.01 mW/cm2.

The general effect on animals of an intense microwave field at a PFM (power flux density) of 0.2-0.3 W/cm21 causes changes in respiration, heart rate and blood pressure, while local effects under the same conditions are accompanied by rapidly passing changes in hemodynamics and respiration, obviously of reflex origin. The regulatory significance of the nervous system when exposed to a microwave field appears when the vagus nerves are transected in animals; at the same time, a smaller increase in breathing is noted, but a more severe hemodynamic disturbance as a result of turning off the regulatory influence of the vagus nerve.

In a frog, a microwave field at 0.3 W/cm2 causes changes in cardiac activity similar to the biphasic effect of a UHF electric field. In the first phase, sometimes short-term, there is an increase in heart rate and intensification, followed by a slowdown and cessation of cardiac activity in diastole. After the cessation of exposure, contractions are restored; Arrhythmias are sometimes observed. These effects are considered thermal due to the high PMT of the microwave field used in the experiments.

Big physiological significance has the use of a low intensity microwave field (PPM 0.05 W/cm2, duration 30 minutes), when dogs usually experience a slight increase in heart rate and the disappearance of respiratory arrhythmia, in some animals a slowdown in rhythm appears. According to electrocardiography, with prolonged repeated exposure to a microwave field, one can judge the activation of compensatory mechanisms and the development of adaptation, which can be disrupted in dogs by stronger exposures. The established changes indicate the development of temporary dystrophic processes in the myocardium and are considered as reflex; within the first hour after exposure, these changes disappear. In dogs with artificially induced myocardial infarction, the use of a microwave field causes an increase in heart rate, a decrease in all electrocardiogram waves in each lead, and the S-T interval rises even more above the isoelectric line. The microwave field worsens the functions of a diseased heart.

When normalizing heart function indicators after an experimental myocardial infarction, the use of a low-intensity microwave field causes phase changes in cardiac activity in animals, which can be considered dystrophic. These changes are observed as overall impact, and locally on the head area. Muscle load in combination with a weak microwave field leads to more permanent changes.

Based on electrocardiographic data, we can conclude that under the influence of the microwave field, biochemical processes in the tissues of the heart change, the severity of which depends on the intensity of exposure to microwaves.

Determination of the electrolytic composition of the peripheral blood of animals by electrophoresis after exposure to an intense microwave field (PPM 0.1-0.2 W/cm2) indicates phase changes in the content of potassium and sodium. Initially, the K/Na ratio in plasma increases and then decreases. When compared with electrocardiographic data, it is clear that after exposure to a high potassium content in the blood, pointed high T waves appear in all leads, and with a low content of potassium, low, flattened ones appear. Based on the change in the ratio of potassium and sodium in the blood, it can be assumed that under the influence of microwaves there is a change in the permeability of cell membranes to intra- and extracellular cations.

Biochemical studies are of great interest for the mechanism of action of the microwave field on the body. The study of redox processes in tissues (liver, kidneys, heart muscle) by determining the activity of enzymes in them (cytochrome oxidase, dehydrase and adenosine triphosphatase) reveals the effect of the microwave field on the body. The use of an intense microwave field (PPM 0.1-0.3 W/cm2) leads to sharp decline redox processes in rabbit tissues; in this case, the thermal effect of the microwave field is manifested. A weak microwave field (PPM 0.005-0.01 W/cm2) causes a noticeable increase in redox processes in tissues. Repeated exposure of rabbits to a microwave field leads to smaller shifts in redox processes compared to a single exposure. This can be explained by the fact that repeated exposure stimulates compensatory and adaptive mechanisms and causes smaller shifts in redox processes in animal tissues. The influence of compensatory mechanisms was more pronounced in the central nervous system than in the heart.

The study of protein metabolism in animals both under local and general exposure to microwave fields revealed some features. Exposure to the heart area daily for 10 days (PPM 0.02 W/cm2 with an emitter area of ​​10 cm2) did not cause any significant changes in the protein metabolism of the heart muscle, but with more intense exposure (PPM 0.1 W/cm2) an increase in the content of proteins with phosphorylase activity while a simultaneous decrease in the myogen fraction.

In the heart muscle of animals, significant changes in the content of individual protein fractions were noted, which depended on the intensity of exposure.

The precipitation reaction in Uchterlon agar was used to study the antigenic composition of the blood serum of animals exposed to general exposure to microwaves in the form of a course of 20 procedures for 10 minutes daily (PPM 0.006 and 0.04 W/cm2). Blood serum was examined on the 24-25th day after the last exposure. The precipitation reaction in agar showed that the general effect of microwaves (PPM 0.006 W/cm2) does not lead to a change in the antigenic composition of animal blood serum. Antiserum to the serum of experimental animals reacted equally with the serum of both experimental and healthy animals.

In immunological studies of the blood serum of animals exposed to general microwave exposure with a PPM of 0.04 W/cm2, a smaller number of precipitation lines were found in the precipitation reaction in agar, which indicated a simplification of the antigenic composition of the blood serum and strengthening of the immune system. Sera versus serum from healthy animals reacted differently with serum from healthy and experimental animals; at the same time, the sera against the experimental serum reacted with the serum of healthy and experimental animals in the same way. The findings appear to indicate that the serum of healthy animals contains antigens that are not present in the serum of microwave-exposed animals.

Simplification of the antigenic composition of blood serum when exposed to thermal doses of microwaves indicates a profound shift in the body's metabolism. No such phenomenon was observed under the influence of non-thermal doses of microwaves.

Study of the higher nervous activity of dogs using the method conditioned reflexes shows that exposure to a microwave field causes significant changes that depend on the power flux density, duration of exposure and typological characteristics of the animal. Change functional state bark cerebral hemispheres brain in dogs was observed even after a single exposure to a weak microwave field (PPM 0.005-0.01 W/cm2). Since this field power did not cause an increase in body temperature, the observed effect was not associated with overheating. A weak microwave field enhanced the process of excitation, and a strong one, in which shortness of breath and overheating were observed, led to the development of inhibition in the central nervous system.

Strengthening both conditional and unconditioned reflexes indicates that the microwave field acts on both the cerebral cortex and subcortical formations. With prolonged exposure to a weak microwave field, phase changes in higher nervous activity are observed: first, an intensification of the excitation process, and then a weakening of it to baseline with increased braking.

The study of electroencephalographic parameters in animals under general exposure revealed a relationship between the nature of the bioelectrical activity of the brain and the intensity of exposure to the microwave field. Intense and prolonged exposure caused changes in the basic rhythms of electrical activity, as well as amplitude. When exposed to the animal's head, these changes appeared under weak influences of the microwave field.

Scientists are currently trying to treat microwave waves malignant tumors, which may finally make it possible to create a unique treatment for breast cancer. However, everything is still in the stage of animal experiments.

Androsova Ekaterina

I. Microwave radiation (a little theory).

II. Impact on humans.

III. Practical application of microwave radiation. Microwave ovens.

1. What is a microwave oven?

2. History of creation.

3. Device.

4. The operating principle of a microwave oven.

5. Key Features:

a. Power;

b. Internal coating;

c. Grill (its varieties);

d. Convection;

IV. Research part of the project.

1. Comparative analysis.

2. Social survey.

V. Conclusions.

Download:

Preview:

Project work

in physics

on the topic:

“Microwave radiation.
Its use in microwave ovens.
Comparative analysis of furnaces from different manufacturers"

11th grade students

GOU Secondary School "Losiny Ostrov" No. 368

Androsova Ekaterina

Teacher - project leader:

Zhitomirskaya Zinaida Borisovna

February 2010

Microwave radiation.

Infrared radiation- electromagnetic radiation occupying spectral region between the red end visible light(with wavelengthλ = 0.74 µm) and microwave radiation (λ ~ 1-2 mm).

Microwave radiation, Ultrahigh frequency radiation(microwave radiation) - electromagnetic radiation including the centimeter and millimeter range of radio waves (from 30 cm - frequency 1 GHz to 1 mm - 300 GHz). High-intensity microwave radiation is used for non-contact heating of bodies, for example, in everyday life and for heat treatment of metals in microwave ovens, as well as for radar. Low-intensity microwave radiation is used in communications, mainly portable (walkie-talkies, latest generation cell phones, WiFi devices).

Infrared radiation is also called “thermal” radiation, since all bodies, solid and liquid, heated to a certain temperature, emit energy in the infrared spectrum. In this case, the wavelengths emitted by the body depend on the heating temperature: the higher the temperature, the shorter the wavelength and the higher the radiation intensity. The radiation spectrum of an absolutely black body at relatively low (up to several thousand Kelvin) temperatures lies mainly in this range.

IR (infrared) diodes and photodiodes are widely used in remote controls remote control, automation systems, security systems, etc. Infrared emitters are used in industry for drying paint surfaces. The infrared drying method has significant advantages over the traditional convection method. First of all, this is, of course, an economic effect. The speed and energy consumed during infrared drying is less than the same indicators with traditional methods. A positive side effect is also the sterilization of food products, increasing the corrosion resistance of painted surfaces. The disadvantage is the significantly greater unevenness of heating, which is completely unacceptable in a number of technological processes. A special feature of the use of IR radiation in the food industry is the possibility of penetration of an electromagnetic wave into capillary-porous products such as grain, cereals, flour, etc. to a depth of up to 7 mm. This value depends on the nature of the surface, structure, material properties and frequency characteristics of the radiation. An electromagnetic wave of a certain frequency range has not only a thermal, but also a biological effect on the product, helping to accelerate biochemical transformations in biological polymers (starch, protein, lipids).

Impact of microwave radiation on humans

The accumulated experimental material allows us to divide all the effects of microwave radiation on living beings into 2 large classes: thermal and non-thermal. The thermal effect in a biological object is observed when it is irradiated with a field with a power flux density of more than 10 mW/cm2, and tissue heating exceeds 0.1 C, otherwise a non-thermal effect is observed. If the processes occurring under the influence of powerful electromagnetic fields of microwaves have received a theoretical description that is in good agreement with experimental data, then the processes occurring under the influence of low-intensity radiation have been poorly studied theoretically. There are even no hypotheses about the physical mechanisms of influence electromagnetic study low intensity on biological objects different levels of development, starting with single cell organism and ending with man, although separate approaches to solving this problem are being considered

Microwave radiation can affect human behavior, feelings, and thoughts;
Affects biocurrents with a frequency from 1 to 35 Hz. As a result, there are disturbances in the perception of reality, increased and decreased tone, fatigue, nausea and headache; Complete sterilization of the instinctive sphere is possible, as well as damage to the heart, brain and central nervous system.

ELECTROMAGNETIC RADIATIONS IN THE RADIO FREQUENCY RANGE (RF EMR).

SanPiN 2.2.4/2.1.8.055-96 Maximum permissible levels of energy flux density in the frequency range 300 MHz - 300 GHz depending on the duration of exposure When exposed to radiation for 8 hours or more, MPL - 0.025 mW per square centimeter, when exposed to 2 hours, MPL - 0.1 mW per square centimeter, and for exposure of 10 minutes or less, MPL - 1 mW per square centimeter.

Practical application of microwave radiation. Microwave ovens

A microwave oven is a household electrical appliance designed for quick cooking or quick heating of food, as well as for defrosting food, using radio waves.

History of creation

American engineer Percy Spencer noticed the ability of microwave radiation to heat food when he worked at the Raytheon company. Raytheon ), which manufactures equipment for radars. According to legend, when he was conducting experiments with another magnetron, Spencer noticed that a piece of chocolate in his pocket had melted. According to another version, he noticed that a sandwich placed on the switched-on magnetron became hot.

The patent for the microwave oven was issued in 1946. The first microwave oven was built by Raytheon and was designed for rapid industrial cooking. Its height was approximately equal to human height, weight - 340 kg, power - 3 kW, which is approximately twice the power of a modern household microwave oven. This stove cost about $3,000. It was used mainly in soldiers' canteens and canteens of military hospitals.

The first mass-produced household microwave oven was produced by the Japanese company Sharp in 1962. Initially, demand for the new product was low.

In the USSR, microwave ovens were produced by the ZIL plant.

Microwave oven device.

Main components:

1. microwave source;
2. magnetron;
3. magnetron high-voltage power supply;
4. control circuit;
5. a waveguide for transmitting microwaves from the magnetron to the chamber;
6. a metal chamber in which microwave radiation is concentrated and where food is placed, with a metallized door;
7. auxiliary elements;
8. rotating table in the chamber;
9. circuits that provide security (“blocking”);
10. a fan that cools the magnetron and ventilates the chamber to remove gases generated during cooking.

Operating principle

Magnetrons convert electrical energy into a high-frequency electric field, which causes water molecules to move, which leads to heating of the product. The magnetron, creating an electric field, directs it along a waveguide into the working chamber in which the product containing water is placed (water is a dipole, since the water molecule consists of positive and negative charges). The effect of an external electric field on the product leads to the fact that the dipoles begin to polarize, i.e. The dipoles begin to rotate. When the dipoles rotate, frictional forces arise, which turn into heat. Since polarization of dipoles occurs throughout the entire volume of the product, which causes its heating, this type of heating is also called volumetric heating. Microwave heating is also called microwave heating, meaning the short length of electromagnetic waves.

Characteristics of microwave ovens

Power.

1. The useful or effective power of a microwave oven, which is important for heating, cooking and defrosting, ismicrowave power and grill power. As a rule, the microwave power is proportional to the volume of the chamber: this microwave and grill power should be sufficient for the amount of food that can be placed in a given microwave oven in the appropriate modes. Conventionally, we can assume that the higher the microwave power, the faster heating and cooking occurs.
2. Maximum power consumption- electrical power, which should also be taken into account, since electricity consumption can be quite high (especially in large microwave ovens with grill and convection). Knowing the maximum power consumption is necessary not only to estimate the amount of electricity consumed, but also to check the possibility of connecting to existing outlets (for some microwave ovens, the maximum power consumption reaches 3100 W).

Internal coatings

The walls of the microwave oven's working chamber have a special coating. There are currently three main options: enamel coating, specialty coatings and stainless steel coating.

1. Durable enamel coating, smooth and easy to clean, found in many microwave ovens.
2. Special coatings, developed by microwave oven manufacturers, are advanced coatings that are even more resistant to damage and intense heat and are easier to clean than conventional enamel. Special or advanced coatings include LG's "antibacterial coating" and Samsung's "bioceramic coating".
3. Stainless steel coating- extremely resistant to high temperatures and damage, it is especially reliable and durable, and also looks very elegant. Stainless steel lining is typically used in grill or convection microwave ovens that have multiple high-temperature settings. As a rule, these are stoves of a high price category, with a beautiful external and internal design. However, it should be noted that keeping such a coating clean requires some effort and the use of special cleaning products.

Grill

Heating element grill. outwardly resembles a black metal tube with a heating element inside, located in the upper part of the working chamber. Many microwave ovens are equipped with a so-called “moving” heating element (TEN), which can be moved and installed vertically or inclined (at an angle), providing heating not from above, but from the side.
The movable heating element grill is especially convenient to use and provides additional features for preparing dishes in grill mode (for example, in some models you can fry chicken in a vertical position). Besides, inner chamber A microwave oven with a movable heating element grill is easier and more convenient to clean (as is the grill itself).

Quartz Quartz grill located at the top of the microwave oven, and is a tubular quartz element behind a metal grid.

Unlike a heating element grill, a quartz grill does not take up space in the working chamber.

The power of a quartz grill is usually less than that of a grill with a heating element; microwave ovens with a quartz grill consume less electricity.

Ovens with a quartz grill roast more gently and evenly, but a grill with a heating element can provide more intense operation (more “aggressive” heating).

There is an opinion that a quartz grill is easier to keep clean (it is hidden in the upper part of the chamber behind a grill and is more difficult to get dirty). However, we note that over time, grease splatters, etc. They may still get on it, and it will no longer be possible to simply wash it, like a heating element grill. There is nothing particularly terrible about this (grease splashes and other contaminants will simply burn off the surface of the quartz grill).

Convection

Microwave ovens with convection are equipped with a ring heating element and a built-in fan (usually located on the back wall, in in some cases- at the top), which evenly distributes the heated air inside the chamber. Thanks to convection, food is baked and fried, and in such an oven you can bake pies, bake chicken, stew meat, etc.

Research part of the project

Comparative analysis of microwave ovens from different manufacturers
Social survey results

Comparison table

A social survey was conducted among high school students.

1. Do you have a microwave oven?

2. Which company? What model?

3. What is the power? Other characteristics?

4. Do you know the safety rules when handling a microwave oven? Do you comply with them?

5. How do you use a microwave oven?

6. Your recipe.

Precautions when using a microwave oven.

1. Microwave radiation cannot penetrate metal objects, so you should not cook food in metal containers. If the metal utensils are closed, then the radiation is not absorbed at all and the oven may fail. Cooking in an open metal container is possible in principle, but its efficiency is an order of magnitude less (since radiation does not penetrate from all sides). In addition, sparks may occur near the sharp edges of metal objects.
2. It is not advisable to place dishes with a metal coating (“golden edge”) in the microwave oven - thin layer metal has high resistance and gets very hot eddy currents, this may destroy the cookware in the area of ​​metal plating. At the same time, metal objects without sharp edges, made of thick metal, are relatively safe in the microwave.
3. You cannot cook liquids in hermetically sealed containers or whole bird eggs in a microwave oven - due to the strong evaporation of water inside them, they will explode.
4. It is dangerous to heat water in the microwave, because it is capable of overheating, that is, heating above the boiling point. A superheated liquid can then boil very sharply and at an unexpected moment. This applies not only to distilled water, but also to any water that contains few suspended particles. The smoother and more uniform the inner surface of the water container, the higher the risk. If the vessel has a narrow neck, then there is a high probability that when it starts boiling, superheated water will spill out and burn your hands.

CONCLUSIONS

Microwave ovens are widely used in everyday life, but some buyers of microwave ovens do not know the rules for handling microwave ovens. This can lead to negative consequences (high dose of radiation, fire, etc.)

Main characteristics of microwave ovens:

1. Power;
2. Availability of grill (heating element/quartz);
3. Presence of convection;
4. Internal coating.

The most popular are microwave ovens from Samsung and Panasonic with a power of 800 W, with a grill, costing about 4000-5000 rubles.

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 broadcast radio radiation in that it is generated by similar methods. Applicable to microwave radiation classical theory radio waves, 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.

A system of radio relay towers required to transmit microwave radiation to long distances, can, of course, only be built on land. For intercontinental communication, a different relay method is required. This is where messengers come to the rescue artificial satellites Earth; 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 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 intercom. Intelsat's latest intercontinental series satellites have been launched into different locations 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, free electrons in it begin to rotate around magnetic field lines in the plane, perpendicular to the direction 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 called cyclotron resonance; it allows you to measure effective mass electron. Such measurements provided a lot of valuable information about electronic properties 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 quantities 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 oscillatory circuit 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 resonant frequencies, so 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 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 vibrations. 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 running 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, you need special methods and specially shaped conductors. 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 become 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 They transmit microwave signals well with frequencies 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 have sufficient large sizes 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 levels internal energy 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 the temperature 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 specific 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 are very diverse 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 Horn antennas, parabolic reflectors, metal and dielectric lenses can serve. 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 length waves, and increasing 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.

Microwave radiation is electromagnetic radiation, which consists of the following ranges: decimeter, centimeter and millimeter. Its wavelength ranges from 1 m (the frequency in this case is 300 MHz) to 1 mm (the frequency is 300 GHz).

Wide practical application Microwave radiation was received during the implementation of a method for non-contact heating of bodies and objects. IN scientific world this discovery intensively used in space exploration. Its usual and best known use is in home microwave ovens. It is used for heat treatment of metals.

Also today, microwave radiation has become widespread in radar. Antennas, receivers and transmitters are actually expensive objects, but they successfully pay for themselves due to the huge information capacity of microwave communication channels. The popularity of its use in everyday life and in production is explained by the fact that this type of radiation is all-penetrating, therefore, the object is heated from the inside.

The scale of electromagnetic frequencies, or rather, its beginning and end, represents two various shapes radiation:

• ionizing (wave frequency greater than the frequency of visible light);
• non-ionizing (radiation frequency less than the frequency of visible light).

Ultra-high-frequency non-ionized radiation is dangerous for humans, which directly affects human biocurrents with a frequency of 1 to 35 Hz. As a rule, non-ionized microwave radiation provokes causeless fatigue, cardiac arrhythmia, nausea, decreased overall tone of the body and severe headache. Such symptoms should be a signal that a harmful source of radiation is nearby, which can cause significant damage to health. However, as soon as the person leaves the danger zone, the malaise stops and these unpleasant symptoms disappear on their own.

Stimulated emission was discovered back in 1916 by the brilliant scientist A. Einstein. He described this phenomenon as the influence of an external electron arising during the transition of an electron in an atom from an upper to a lower one. The radiation that arises in this case is called induced radiation. It has another name - stimulated emission. Its peculiarity is that the atom emits electromagnetic wave- its polarization, frequency, phase, and direction of propagation are the same as that of the original wave.

Scientists used modern lasers as a basis for their operation, which, in turn, helped in the creation of fundamentally new modern devices- for example, quantum hygrometers, brightness amplifiers, etc.

Thanks to the laser, new technical areas have emerged - such as laser technologies, holography, nonlinear and integrated optics, and laser chemistry. It is used in medicine for complex eye surgeries and surgery. The monochromaticity and coherence of the laser make it indispensable in spectroscopy, isotope separation, measurement systems and in light detection.

Microwave radiation is also radio radiation, only it belongs to the infrared range, and also has highest frequency in the radio range. We encounter this radiation several times a day, using a microwave oven to heat food, and also when talking on a mobile phone. Astronomers have found very interesting and important applications for it. Microwave radiation is used to study space background or times big bang, which happened billions of years ago. Astrophysicists are studying inhomogeneities in the glow in some parts of the sky, which helps to understand how galaxies formed in the Universe.