The group of electromagnetic waves is represented by numerous subspecies that are of natural origin. This category also includes microwave radiation, which is also called microwave radiation. In short, this term is called the abbreviation microwave. The frequency range of these waves is located between infrared rays and radio waves. This type of irradiation cannot boast of a large extent. This figure varies from 1 mm to 30 cm maximum.

Primary sources of microwave radiation

Many scientists have tried to prove the negative effects of microwaves on humans in their experiments. But in the experiments they carried out, they focused on various sources of such radiation that were of artificial origin. But in real life, people are surrounded by many natural objects that produce such radiation. With their help, man went through all stages of evolution and became what he is today.

With the development of modern technologies, natural sources of radiation, such as the Sun and other space objects, have been joined by artificial ones. The most common among them are usually called:

• radar spectrum installations;
• radio navigation equipment;
• systems for satellite television;
• Cell phones;
• microwave ovens.

The principle of the effect of microwaves on the body

In the course of numerous experiments where the effects of microwaves on humans were studied, scientists found that such rays do not have an ionizing effect.

Ionized molecules are defective particles of substances that lead to the initiation of chromosome mutation. Because of this, the cells become defective. Moreover, predicting which organ will be affected is quite problematic.

Research on this topic has led scientists to the conclusion that when dangerous rays hit the tissues of the human body, they partially begin to absorb the incoming energy. Because of this, high-frequency currents are excited. With their help, the body heats up, which leads to increased blood circulation.

If the irradiation was in the nature of a local lesion, then heat removal from the heated areas can occur very quickly. If a person has fallen under the general flow of radiation, then he does not have such an opportunity. Due to this, the danger of exposure to rays increases several times.

The most important danger when exposed to microwave radiation on humans is considered to be the irreversibility of the reactions that occur in the body. This is explained by the fact that blood circulation here acts as the main link in cooling the body. Since all organs are connected to each other by blood vessels, the thermal effect is expressed very clearly. The most unprotected part of the body is the eye lens. At first it begins to gradually become cloudy. And with prolonged irradiation, which is regular, the lens begins to collapse.

In addition to the lens, a high probability of serious damage remains in a number of other tissues, which contain a lot of liquid components. This category includes:

• blood,
• lymph,
• mucous membrane of the digestive organs from the stomach to the intestines.

Even short-term but powerful radiation leads to the fact that a person will begin to experience a number of abnormalities such as:

• changes in the blood;
• problems with the thyroid gland;
• reducing the efficiency of metabolic processes in the body;
• problems with psychological state.

In the latter case, even depressive states are possible. Some patients who experienced radiation on themselves and at the same time had an unstable psyche even attempted suicide.

Another danger of these invisible rays is the cumulative effect. If initially the patient may not experience any discomfort even during the irradiation itself, after a while it will make itself felt. Due to the fact that at an early stage it is difficult to trace any characteristic symptoms, patients often attribute their unhealthy state to general fatigue or accumulated stress. And at this time, various pathological conditions begin to form in them.

At the initial stage, the patient may experience standard headaches, as well as get tired quickly and have difficulty sleeping. He begins to develop problems with blood pressure stability and even heart pain. But many people attribute even these alarming symptoms to constant stress due to work or difficulties in family life.

Regular and prolonged irradiation begins to destroy the body at a deep level. Because of this, high-frequency radiation was considered dangerous to living organisms. The research revealed that a young body is more susceptible to the negative influence of the electromagnetic field. This is explained by the fact that children have not yet managed to form reliable immunity for at least partial protection from negative external influences.

Signs of exposure and stages of its development

First of all, various neurological disorders develop from such influence. It can be:

• increased fatigue,
• decreased labor productivity,
• headache,
• dizziness,
• drowsiness or vice versa – insomnia,
• irritability,
• weakness and lethargy,
• profuse sweating,
• memory problems
• feeling of a rush to the head.

Microwave radiation affects humans not only in terms of physiological aspects. In severe cases of the disease, even fainting, uncontrollable and unreasonable fear and hallucinations are possible.

The cardiovascular system suffers no less strongly from radiation. A particularly striking effect is seen in the category of neurocirculatory dystonia disorder:

• shortness of breath even without significant physical activity;
• pain in the heart area;
• a shift in the heartbeat rhythm, including “fading” of the heart muscle.

If during this period a person consults a cardiologist, the doctor may detect hypotension and muffled heart muscle tones in the patient. In rare cases, the patient even has a systolic murmur at the apex.

The picture looks a little different if a person is exposed to microwaves on an irregular basis. In this case, he will have:

• slight malaise,
• feeling tired for no reason;
• pain in the heart area.

During physical activity, the patient will experience shortness of breath.

Schematically, all types of chronic exposure to microwaves can be divided into three stages, which differ in the degree of symptomatic severity.

The first stage provides for the absence of characteristic signs of asthenia and neurocirculatory dystonia. Only isolated symptomatic complaints can be traced. If you stop irradiation, then after a while all the unpleasant sensations disappear without additional treatment.

At the second stage, more distinct signs are visible. But at this stage the processes are still reversible. This means that with proper and timely treatment, the patient will be able to regain his health.

The third phase is very rare, but still occurs. In this situation, a person experiences hallucinations, fainting, and even disturbances associated with sensitivity. An additional symptom may be coronary insufficiency.

Biological effect of microwave fields

Since each organism has its own unique characteristics, the biological effect of radiation may also vary from case to case. Several fundamental principles underlie the identification of the severity of a lesion:

• radiation intensity,
• period of influence,
• wavelength,
• the original state of the body.

The last point includes chronic or genetic diseases of the individual victim.

The main danger from radiation is the thermal effect. It involves an increase in body temperature. But doctors also detect non-thermal effects in such cases. In such a situation, a classic increase in temperature does not occur. But physiological changes are still observed.

Thermal effects under the prism of clinical analysis imply not only a rapid increase in temperature, but also:

• increased heart rate,
• shortness of breath,
• high blood pressure,
• increased salivation.

If a person was exposed to low-intensity rays for only 15-20 minutes, which did not exceed the maximum permissible standards, then he experiences various changes in the nervous system at the functional level. They all have varying degrees of expression. If several identical repeated irradiations are performed, the effect accumulates.

How to protect yourself from microwave radiation?

Before looking for methods of protection from microwave radiation, you first need to understand the nature of the influence of such an electromagnetic field. There are several factors to consider here:

• distance from the supposed source of the threat;
• exposure time and intensity;
• impulsive or continuous type of irradiation;
• some external conditions.

To calculate a quantitative assessment of the danger, experts introduced the concept of radiation density. In many countries, experts accept 10 microwatts per centimeter as the standard for this issue. In practice, this means that the power of the flow of hazardous energy in the place where a person spends most of his time should not exceed this permissible limit.

Every person who cares about their health can independently protect themselves from possible danger. To do this, it is enough to simply reduce the amount of time spent near artificial sources of microwave rays.

A different approach to solving this problem is necessary for those people whose work is closely related to exposure to microwaves of various manifestations. They will need to use special protective equipment, which are divided into two types:

• individual,
• are common.

To minimize possible negative consequences from the influence of such radiation, it is important to increase the distance from the worker to the source of radiation. Other effective measures to block the possible negative influence of rays are usually called:

• changing the direction of the rays;
• reduction of radiation flux;
• reducing the time period of exposure;
• use of a screening tool;
• remote control of dangerous objects and mechanisms.

All existing protective screens aimed at preserving user health are divided into two subtypes. Their classification involves division according to the properties of the microwave radiation itself:

• reflective
• absorbing.

The first version of protective equipment is created on the basis of a metal mesh, or sheet metal and metallized fabric. Since the range of such assistants is quite large, employees of various hazardous industries will have plenty to choose from.

The most common versions are sheet screens made of homogeneous metal. But for some situations this is not enough. In this case, it is necessary to enlist the support of multi-layer packages. Inside they will have layers of insulating or absorbent material. It can be ordinary shungite or carbon compounds.

The enterprise security service usually always pays special attention to personal protective equipment. They provide special clothing, which is created on the basis of metallized fabric. It can be:

• robes,
• aprons,
• gloves,
• capes with hoods.

When working with a radiation object or in dangerous proximity to it, you will additionally need to use special glasses. Their main secret is coating with a layer of metal. With this precaution it will be possible to reflect the rays. In total, wearing personal protective equipment can reduce radiation exposure by up to a thousand times. It is recommended to wear glasses at radiation levels of 1 µW/cm.

Benefits of microwave radiation

In addition to the popular belief about how harmful microwaves are, there is also the opposite statement. In some cases, microwaves can even bring benefits to humanity. But these cases must be carefully studied, and the radiation itself must be carried out in doses under the supervision of experienced specialists.

The therapeutic benefits of microwave radiation are based on its biological effects that occur during physical therapy. Special medical generators are used to generate beams for therapeutic purposes (called stimulation). When they are activated, radiation begins to be produced according to parameters clearly defined by the system.

Here, the depth specified by the expert is taken into account so that the heating of the tissues gives the promised positive effect. The main advantage of this procedure is the ability to provide high-quality analgesic and antipruritic therapy.

Medical generators are used around the world to help people who suffer from:

• frontitis,
• sinusitis,
• trigeminal neuralgia.

If the equipment uses microwave radiation with increased penetrating power, then with its help doctors successfully cure a number of diseases in the following areas:

• endocrine,
• respiratory,
• gynecological,
• kidneys

If you follow all the rules prescribed by the safety commission, then the microwave will not cause significant harm to the body. Direct evidence of this is its use for medicinal purposes.

But if you violate operating rules by refusing to voluntarily limit yourself from strong sources of radiation, this can lead to irreparable consequences. Because of this, it is always worth remembering how dangerous microwaves can be when used unsupervised.

12 882

In order to understand whether a microwave oven is harmful, you need to have an idea of ​​what microwaves are. To do this, let us turn not to rumors, but to the scientific data of physics, which explains the nature and properties of all physical phenomena.

What are microwaves and their place in the spectrum of electromagnetic radiation.
Microwave is a type of electromagnetic radiation. And, as you know, electromagnetic radiation from the Sun is the main source of energy for life on Earth. It consists of visible and invisible radiation.

All the colors we see are the visible part of radiation. Invisible is radio waves, infrared (thermal), ultraviolet, x-ray and gamma radiation. All these waves are manifestations of the same phenomenon - electromagnetic radiation, but they differ in wavelength and oscillation frequency. The longer the wavelength, the lower the frequency of their oscillations. These parameters determine the properties of a particular type of radiation.

The entire spectrum of electromagnetic waves can be sequentially arranged as the wavelength decreases (and, accordingly, the oscillation frequency increases) in the following order:

1. Radio waves— electromagnetic waves with a wavelength of more than 1 mm. They include: a) Long waves - wavelength from 10 km to 1 km (frequency 30 kHz - 300 kHz);
   b) Medium waves - wavelength from 1 km to 100 m (frequency 300 kHz -3 MHz);
   c) Short waves - wavelength from 100 m to 10 m (frequency 3 - 30 MHz);
   d) Ultrashort waves with a wavelength less than 10 m (frequency 30 MHz - 300 GHz). Ultrashort waves, in turn, are divided into:
   meter, centimeter (including microwaves), millimeter waves.
   Microwave is a type of electromagnetic energy that falls on the frequency scale between radio waves and infrared radiation. Therefore, they share some of the properties of their neighbors. Microwave or ultra-high frequency waves (microwaves) are short electromagnetic radio waves with a wavelength of 1 mm - 1 m (frequency less than 300 MHz). It is called ultra-high frequency (microwave) radiation because it has the highest frequency in the radio range. The physical nature of microwave radiation is the same as that of radio waves. They are used for telephone communications, Internet operation, transmission of television programs, and in microwave ovens.
2. Infrared radiation- electromagnetic waves with a wavelength of 1 mm - 780 nm (frequency 300 GHz - 429 THz). It is also called “thermal” radiation, since it is perceived by the human skin as a feeling of warmth.
3. Visible radiation— electromagnetic waves with a wavelength of 780-380 nm (frequency 429 THz - 750 THz).
4. Ultraviolet radiation e - electromagnetic waves with a wavelength of 380 - 10 nm (frequency 7.5 1014 Hz - 3 1016 Hz).
5. X-ray radiation- electromagnetic waves with a wavelength of 10 nm - 5 pm (frequency 3 1016 - 6 1019 Hz).
6. Gamma rays— electromagnetic waves with a wavelength less than 5 pm (frequency more than 6 1019 Hz).

The amount of energy it carries depends on the wavelength and frequency. Waves with long wavelengths and low frequencies carry little energy. There are many waves with short wavelength and high frequency. The more energy the radiation has, the more destructive effect it has on a person.

Based on their ability to cause an effect such as ionization of a substance, all of the above types of electromagnetic radiation are divided into 2 categories: ionizing And non-ionizing.
These 2 types of radiation differ in the amount of energy they carry.

1. Ionizing radiation otherwise called radioactive. This includes x-rays, gamma radiation, and in some cases ultraviolet.
Ionizing radiation It is characterized by high energy, capable of ionizing substances, and causes changes in cells that disrupt the course of biological reactions in the body and pose a health hazard.
The maximum energy is inherent in gamma radiation. As a result of its exposure, food becomes radioactive, and a person develops radiation sickness. That is why exposure to all ionizing radiation is very dangerous for a living organism.

2. Non-ionizing radiation - radio waves, infrared, visible radiation.
These types of radiation do not have enough energy to ionize matter, so they cannot change the structure of atoms and molecules. The boundary between non-ionizing and ionizing radiation is usually considered to be a wavelength of approximately 100 nanometers.
The energy of long radio waves is not even enough to heat anything - they will simply pass right through any food. The energy of infrared radiation (thermal) is absorbed by all objects, including food, therefore it is successfully used, for example, in toasters. Microwaves occupy a middle position and therefore also have low energy.

Microwaves used in microwave ovens.
Household microwave ovens use microwaves with a radiation frequency of 2450 MHz (2.45 GHz) and a wavelength of approximately 12 cm. These indicators are significantly lower than the frequencies of x-rays and gamma rays, which cause an ionizing effect and are dangerous to humans. Microwaves are located between radio and infrared waves, i.e. they have insufficient energy to ionize atoms and molecules.
In working microwave ovens, microwaves do not directly affect humans. They are absorbed by food, causing a heat-generating effect.
Microwave ovens do not create ionizing radiation and do not emit radioactive particles, therefore they do not have a radioactive effect on living organisms and food. They generate radio waves, which, according to all the laws of physics, cannot change the atomic-molecular structure of a substance; they can only heat it.
So, microwaves are a type of radio waves. Being on the frequency scale between radio waves and infrared radiation, they share properties with them.
However, neither the heat nor the radio waves that surround us have any effect on food, and therefore there is little reason to expect the same from microwaves.

On the same topic:

The range of radio emission is the opposite of gamma radiation and is also unlimited on one side - from long waves and low frequencies.

Engineers divide it into many sections. The shortest radio waves are used for wireless data transmission (Internet, cellular and satellite telephony); meter, decimeter and ultrashort waves (VHF) occupy local television and radio stations; short waves (HF) are used for global radio communications - they are reflected from the ionosphere and can circle the Earth; medium and long waves are used for regional radio broadcasting. Ultra-long waves (ELW) - from 1 km to thousands of kilometers - penetrate salt water and are used for communication with submarines, as well as for searching for minerals.

The energy of radio waves is extremely low, but they excite weak vibrations of electrons in a metal antenna. These vibrations are then amplified and recorded.

The atmosphere transmits radio waves with a length from 1 mm to 30 m. They make it possible to observe the nuclei of galaxies, neutron stars, and other planetary systems, but the most impressive achievement of radio astronomy is record-breaking detailed images of cosmic sources, the resolution of which exceeds a ten-thousandth of an arc second.

Microwave

Microwaves are a subband of radio emission adjacent to the infrared. It is also called ultra-high frequency (microwave) radiation because it has the highest frequency in the radio range.

The microwave range is of interest to astronomers because it detects the relict radiation remaining from the time of the Big Bang (another name is the microwave cosmic background). It was emitted 13.7 billion years ago, when the hot matter of the Universe became transparent to its own thermal radiation. As the Universe expanded, the CMB cooled and today its temperature is 2.7 K.

CMB radiation comes to Earth from all directions. Today, astrophysicists are interested in inhomogeneities in the sky glow in the microwave range. They are used to determine how clusters of galaxies began to form in the early Universe in order to test the correctness of cosmological theories.

But on Earth, microwaves are used for such mundane tasks as heating breakfast and talking on a cell phone.

The atmosphere is transparent to microwaves. They can be used to communicate with satellites. There are also projects for transmitting energy over a distance using microwave beams.

Sources

Sky Reviews

Microwave sky 1.9 mm(WMAP)

The cosmic microwave background, also called the cosmic microwave background radiation, is the cooled glow of the hot Universe. It was first discovered by A. Penzias and R. Wilson in 1965 (Nobel Prize 1978). The first measurements showed that the radiation is completely uniform throughout the sky.

In 1992, the discovery of anisotropy (inhomogeneity) of the cosmic microwave background radiation was announced. This result was obtained by the Soviet satellite Relikt-1 and confirmed by the American COBE satellite (see Sky in the infrared). COBE also determined that the spectrum of the cosmic microwave background radiation is very close to that of the blackbody. The 2006 Nobel Prize was awarded for this result.

Variations in the brightness of the cosmic microwave background radiation across the sky do not exceed one hundredth of a percent, but their presence indicates subtle inhomogeneities in the distribution of matter that existed at an early stage of the evolution of the Universe and served as the embryos of galaxies and their clusters.

However, the accuracy of the COBE and Relict data was not enough to test cosmological models, and therefore in 2001 a new, more accurate WMAP (Wilkinson Microwave Anisotropy Probe) apparatus was launched, which by 2003 had built a detailed map of the intensity distribution of the cosmic microwave background radiation across the celestial sphere. Based on these data, cosmological models and ideas about the evolution of galaxies are now being refined.

CMB arose when the age of the Universe was about 400 thousand years and, due to expansion and cooling, it became transparent to its own thermal radiation. Initially, the radiation had a Planck (blackbody) spectrum with a temperature of about 3000 K and accounted for the near-infrared and visible ranges of the spectrum.

As the Universe expanded, the cosmic microwave background radiation experienced a red shift, which led to a decrease in its temperature. Today the temperature of the cosmic microwave background radiation is 2.7 TO and it falls in the microwave and far-infrared (submillimeter) ranges of the spectrum. The graph shows an approximate view of the Planck spectrum for this temperature. The spectrum of the cosmic microwave background radiation was first measured by the COBE satellite (see Sky in the infrared), for which the Nobel Prize was awarded in 2006.

Radio sky on wave 21 cm, 1420 MHz(Dickey & Lockman)

Famous spectral line with wavelength 21.1 cm is another way to observe neutral atomic hydrogen in space. The line arises due to the so-called hyperfine splitting of the main energy level of the hydrogen atom.

The energy of an unexcited hydrogen atom depends on the relative orientation of the spins of the proton and electron. If they are parallel, the energy is slightly higher. Such atoms can spontaneously transform into a state with antiparallel spins, emitting a quantum of radio emission that carries away a tiny excess of energy. This happens to an individual atom on average once every 11 million years. But the huge distribution of hydrogen in the Universe makes it possible to observe gas clouds at this frequency.

Radio sky on wave 73.5 cm, 408 MHz(Bonn)

This is the longest wavelength of all sky surveys. It was performed at a wavelength at which a significant number of sources are observed in the Galaxy. In addition, the choice of wavelength was determined by technical reasons. To construct the survey, one of the world's largest full-rotating radio telescopes was used - the 100-meter Bonn radio telescope.

Terrestrial Application

The main advantage of a microwave oven is that over time the food is heated throughout the entire volume, and not just from the surface.

Microwave radiation, having a longer wavelength, penetrates deeper than infrared radiation under the surface of products. Inside food, electromagnetic vibrations excite rotational levels of water molecules, the movement of which mainly causes heating of food. In this way, microwave (microwave) drying of food, defrosting, cooking and heating takes place. Also, alternating electric currents excite high frequency currents. These currents can occur in substances where mobile charged particles are present.

But sharp and thin metal objects cannot be placed in a microwave oven (this especially applies to dishes with metal decorations coated with silver and gold). Even a thin ring of gold plating along the edge of the plate can cause a powerful electrical discharge that will damage the device that creates the electromagnetic wave in the furnace (magnetron, klystron).

The operating principle of cellular telephony is based on the use of a radio channel (in the microwave range) for communication between the subscriber and one of the base stations. Information is transmitted between base stations, as a rule, via digital cable networks.

The range of the base station - the size of the cell - is from several tens to several thousand meters. It depends on the landscape and on the signal strength, which is selected so that there are not too many active subscribers in one cell.

In the GSM standard, one base station can support no more than 8 telephone conversations simultaneously. During mass events and natural disasters, the number of callers increases sharply, this overloads base stations and leads to interruptions in cellular communications. For such cases, cellular operators have mobile base stations that can be quickly delivered to areas with large crowds of people.

There is a lot of controversy about the possible harm of microwave radiation from cell phones. During a conversation, the transmitter is in close proximity to the person's head. Repeated studies have not yet been able to reliably register the negative effects of radio emissions from cell phones on health. Although the effects of weak microwave radiation on body tissue cannot be completely ruled out, there is no cause for serious concern.

Television images are transmitted on meter and decimeter waves. Each frame is divided into lines along which the brightness changes in a certain way.

The transmitter of a television station constantly broadcasts a radio signal of a strictly fixed frequency, it is called the carrier frequency. The receiving circuit of the TV is adjusted to it - a resonance arises in it at the desired frequency, which makes it possible to pick up weak electromagnetic oscillations. Information about the image is transmitted by the amplitude of the oscillations: large amplitude means high brightness, low amplitude means a dark area of ​​the image. This principle is called amplitude modulation. Sound is transmitted similarly by radio stations (except FM stations).

With the transition to digital television, the rules for image encoding change, but the very principle of the carrier frequency and its modulation remains the same.

Parabolic antenna for receiving a signal from a geostationary satellite in the microwave and VHF ranges. The principle of operation is the same as that of a radio telescope, but the dish does not need to be made movable. At the time of installation, it is directed to the satellite, which always remains in one place relative to earthly structures.

This is achieved by placing the satellite into a geostationary orbit at an altitude of about 36 thousand. km above the Earth's equator. The period of revolution along this orbit is exactly equal to the period of rotation of the Earth around its axis relative to the stars - 23 hours 56 minutes 4 seconds. The size of the dish depends on the power of the satellite transmitter and its radiation pattern. Each satellite has a primary service area where its signals are received by a dish with a diameter of 50–100 cm, and the peripheral zone, where the signal quickly weakens and an antenna of up to 2–3 may be required to receive it. m.

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. Main characteristics:

a. Power;

b. Internal coating;

c. Grill (its varieties);

d. Convection;

IV. Research part of the project.

1. Comparative analysis.

2. Social poll.

V. Conclusions.

Download:

Preview:

Project work

in physics

on the topic of:

“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 the spectral region between the red end of visible light (with a 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, 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 not even hypotheses about the physical mechanisms of the impact of low-intensity electromagnetic studies on biological objects of different levels of development, from a single-celled organism to humans, although individual 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, disturbances in the perception of reality, increased and decreased tone, fatigue, nausea and headache occur; 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 quickly cooking or quickly heating 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.

Principle of operation

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, 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 opportunities for preparing dishes in grill mode (for example, in some models you can fry chicken in a vertical position). In addition, the inner chamber of 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 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 undesirable to place dishes with a metal coating (“golden border”) in a microwave oven - a thin layer of metal has a high resistance and is highly heated by eddy currents, this can destroy the dishes in the area of ​​the metal coating. 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 the 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.

>Microwaves

Explore power and influence microwaves. Read about microwave ranges, frequency and length of radiation, what microwave sources are, and how an oven works.

Microwave– electromagnetic waves with a length of 1 m – 1 mm).

Learning Objective

• Understand the three microwave bands.

Main points

• The microwave region is overlapped by the highest frequency waves.
• The "micro" prefix in a microwave oven does not indicate wavelength.
• Microwaves are divided into three bands: extremely high frequency (30-300 GHz), ultra-high frequency (3-30 GHz) and ultra-high frequency (300 MHz-3 GHz).
• The list of sources includes artificial devices such as transmitting towers, radars, masers, as well as natural ones - the Sun and cosmic microwave background radiation.
• Microwaves can be produced from atoms and molecules. They absorb and emit rays if the temperature rises above absolute zero.

Terms

• Radar - a method of searching for distant objects and indicating their position, speed and other characteristics through the analysis of sent radio waves reflected from the surface.
• Thermal excitement is the thermal movement of atoms and molecules if the temperature in an object is above absolute zero.
• Terahertz radiation is electromagnetic waves whose frequencies approach the terahertz.

Microwave

Microwaves are electromagnetic waves whose wavelength exists in the range of 1m - 1mm (300 MHz - 300 GHz). The microwave region is usually overlapped by the highest frequency waves. They are able to move in vacuum conditions at the speed of light.

The prefix "micro" in "microwave" does not indicate a wavelength in the micrometer range. This just means that microwaves appear small because they have shorter wavelengths compared to radio broadcasts. The division between different types of rays is most often arbitrary.

Here are the main categories of electromagnetic waves. Dividing lines differ in some places, and other categories may overlap. Microwaves occupy the high-frequency portion of the radio section of the electromagnetic spectrum

Subcategories of microwaves

Microwaves are divided into three ranges:

• extremely high frequency (30-300 Hz). If the indicators are higher, then we are faced with far-IR light, also called terahertz radiation. This band is most often used in radio astronomy and remote sensing.
• ultra-high frequency (3-30 GHz). It is called the centimeter band because the frequency varies between 10-1 cm. The range is applicable in radar transmitters, microwave ovens, communications satellites and short terrestrial channels for transporting data.
• Ultra-high frequency (300 MHz - 3 GHz) is the decimeter range, as the wavelength ranges from 10 cm to 1 m. They are present in television broadcasting, wireless telephone communications, walkie-talkies, satellites, etc.

Microwave sources

These are high-frequency electromagnetic waves created by currents in macroscopic circuits and devices. They can also be obtained from atoms and molecules if they act as part of electromagnetic rays formed during thermal stirring.

It's important to remember that more information is transmitted at higher frequencies, which is why microwaves are great for communication devices. Due to the short wavelengths, a clear line of sight must be established between the transmitter and receiver.

The Sun also produces microwave rays, although most are blocked by the planetary atmosphere. CMB radiation permeates all space. Its finding confirms the Big Bang theory.

CMB radiation from the Big Bang with increased expansion

Devices with microwaves

High power microwave sources use special vacuum tubes to generate microwaves. The devices operate on various principles using the ballistic movement of electrons in a vacuum. They are affected by electric or magnetic fields.

Magnetron cavity used in a microwave oven

Microwave ovens use microwaves to heat food. The required frequencies of 2.45 GHz are created thanks to the acceleration of electrons. After which an alternating electric field is formed in the oven.

Water and some food components have a negative charge at one end and a positive charge at the other. The range of microwave frequencies is selected in such a way that polar molecules, in an attempt to preserve their positions, absorb energy and increase temperature indicators (dielectric heating).

Radar during World War II used microwaves. Finding and synchronizing microwave echoes can calculate the distance to objects such as clouds or aircraft. The Doppler shift in a radar echo can indicate the speed of a vehicle or even the intensity of a rainstorm. More complex systems display our and other planets. A maser is a laser-like device that increases light energy by stimulating photons.