Electromagnetic radiation definition. Reception of electromagnetic waves and scattering phenomenon

Electromagnetic radiation exists exactly as long as our Universe lives. It has played a key role in the evolution of life on Earth. In fact, this is a perturbation of the state of the electromagnetic field propagating in space.

Characteristics of electromagnetic radiation

Any electromagnetic wave is described using three characteristics.

1. Frequency.

2. Polarization.

Polarization- one of the main wave attributes. Describes the transverse anisotropy electromagnetic waves. Radiation is considered polarized when all wave oscillations occur in the same plane.

This phenomenon is actively used in practice. For example, in the cinema when showing 3D films.

With the help of polarization, IMAX glasses separate the image, which is intended for different eyes.

Frequency is the number of wave crests that pass by the observer (in this case, the detector) in one second. Measured in hertz.

Wavelength- specific distance between nearest points electromagnetic radiation, oscillations of which occur in one phase.

Electromagnetic radiation can propagate in almost any medium: from dense matter to vacuum.

The speed of propagation in vacuum is 300 thousand km per second.

Interesting video about the nature and properties of EM waves, see the video below:

Types of electromagnetic waves

All electromagnetic radiation is divided by frequency.

1. Radio waves. There are short, ultra-short, extra-long, long, medium.

The length of radio waves ranges from 10 km to 1 mm, and from 30 kHz to 300 GHz.

Their sources can be both human activities and various natural atmospheric phenomena.

2. . The wavelength lies within 1mm - 780nm, and can reach up to 429 THz. Infrared radiation is also called thermal radiation. The basis of all life on our planet.

3. Visible light. Length 400 - 760/780nm. Accordingly, it fluctuates between 790-385 THz. This includes the entire spectrum of radiation that can be seen by the human eye.

4. . The wavelength is shorter than in infrared radiation.

It can reach up to 10 nm. such waves is very large - about 3x10 ^ 16 Hz.

5. X-rays. waves 6x10 ^ 19 Hz, and the length is about 10 nm - 5 pm.

6. Gamma waves. This includes any radiation, which is greater than in x-rays, and the length is less. The source of such electromagnetic waves are cosmic, nuclear processes.

Scope of application

Somewhere from late XIX century, all human progress has been associated with the practical application of electromagnetic waves.

The first thing worth mentioning is radio communication. She made it possible for people to communicate, even if they were far from each other.

Satellite broadcasting, telecommunications are further development primitive radio.

It is these technologies that have shaped the information image of modern society.

Sources of electromagnetic radiation should be considered both large industrial facilities and various lines power lines.

Electromagnetic waves are actively used in military affairs (radar, complex electrical devices). Also, medicine has not done without their use. Infrared radiation can be used to treat many diseases.

X-rays help identify damage to a person's internal tissues.

With the help of lasers, a number of operations are carried out that require jewelry precision.

Importance of electromagnetic radiation in practical life It's hard to overestimate a person.

Soviet video about the electromagnetic field:

Possible negative impact on humans

Despite their usefulness, strong sources of electromagnetic radiation can cause the following symptoms:

Fatigue;

Headache;

Nausea.

Excessive exposure to certain types of waves cause damage internal organs, central nervous system, brain. Changes in the human psyche are possible.

An interesting video about the effect of EM waves on a person:

To avoid such consequences, almost all countries of the world have standards governing electromagnetic safety. Each type of radiation has its own regulatory documents (hygienic standards, radiation safety standards). The effect of electromagnetic waves on humans is not fully understood, therefore WHO recommends minimizing their impact.

With constant development high technology there is an increasing number of sources of harmful rays that surround man and nature from all sides. The issues of electromagnetic radiation and its influence on the human body are being discussed today by world-class scientists.

Completely restrict yourself from exposure harmful radiation it is not possible, but it is possible and necessary to prevent their excess, it is enough to understand what it is.

One of the proven facts of the impact of electro magnetic field becomes his Negative influence not only on human health, but also on his thoughts, behavior and even the psychological component. Scientists came to this conclusion after studying the long-term interaction of waves with the human body. The sources of these waves are all kinds of electronic devices, computer, WI-FI, power lines and much more.

Thus, based on research, experts have revealed the theory that developing diseases and pathologies in the human body take place due to the influence of rays from the outside. Moreover, decay products can even cause poisoning of body cells. Fortunately, a person can protect himself and his loved ones from harmful waves by knowing the elementary methods of protection against electromagnetic radiation.

Types of electromagnetic radiation are divided into radio waves, infrared (thermal) radiation, visible (optical) radiation, ultraviolet and hard radiation. IMPORTANT: in this case, the answer to the question “does visible light belong to electromagnetic radiation” is positive.

radio wave sickness

By the beginning of the 60s, specialists managed to discover a new trend in medicine - radio wave disease. The spectrum of distribution of this disease is very wide - 1/3 of the population. It cannot be said that in most cases a person is exposed to waves against his will. However, radio wave disease is already indicated by a number of symptoms, including:

• headache;
• dizziness;
• increased fatigue;
• sleep disturbance;
• depression;
• distraction of attention.

Since such symptoms apply to many varieties of diseases, diagnosing the above becomes extremely problematic. But, like any disease, radio wave is able to develop and progress.

As a result of its spread throughout the body, a person runs the risk of developing cardiac arrhythmias, chronic respiratory diseases, and even fluctuations in blood sugar levels. This happens through the destruction of the electromagnetic field of a person, affecting even the cells of his body.

This disease manifests itself in different ways depending on the organ or system that it affects:

1. Nervous system- we are talking about the deterioration of the conductivity of neurons - the nerve cells of the brain, which are susceptible to electromagnetic radiation that affects a person. Thus, a deformation occurs in their work, which leads to a violation of conditioned and unconditioned reflexes, a deterioration in the functioning of the limbs, the appearance of hallucinations, and irritability. Cases of suicide attempts have been reported developing disease.
2. Immune system - in this case, immunity suppression occurs. And the cells responsible for its protection are themselves susceptible to the influence of electromagnetic waves, thus creating an additional negative influence from all sides.
3. Blood - electrical frequencies provoke the adhesion of blood cells to each other, contributing to the deterioration of blood outflow, the formation of blood clots. Thus, an extra release of adrenaline into the body can occur, which in itself is detrimental to health. There is no need to talk about a violation of the cardiovascular system - an obvious arrhythmia, the development of plaques in the heart muscle and other types of heart failure, as a negative effect of electromagnetic waves on the human body.
4. Endocrine system - since this system is responsible for controlling the functioning of hormones in the body, the influence of electromagnetic fields speaks for itself. The derivative of this influence is the destruction of the liver.
5. Reproductive system - often women are more affected by electromagnetic radiation than men. Possessing increased sensitivity to external influences, the female body is able to literally "suck" harmful radiation. This effect is especially dangerous during pregnancy. In the first weeks, the fetus is not strongly attached to the placenta, so there is a high probability of losing contact with the mother with a sharp release of radiation. With regards to later dates, the statistics are such that electromagnetic radiation affects the change in the genetic code of the child, the deformation of DNA.

Consequences of EMP

Radio wave sickness annually acquires new forms, expanding and progressing, depending on the number and level of radiation sources. Experts have identified a number of consequences not only individually, but also in a large-scale sense:

• Cancer is no secret that oncological diseases manifest themselves in completely different conditions. However, scientists have proven an increase in the negative effects of electromagnetic radiation on cancer cells. Thus, studies in Japan have confirmed the presence of an increased risk of childhood leukemia in people whose bedrooms literally “glow” from the presence of electrical appliances and their components.
• Violation of the psyche - in recent years, cases of deterioration in the perception of the surrounding world have become more frequent in those exposed to an excessive level of electromagnetic radiation. This is not only about the so-called classic symptoms, but also about the developing fear of EMR. Such fear often develops into a phobia, a person begins to panic at the thought that any emission of radiation can provoke painful sensations in one or another organ or part of the body.
• Stillbirth - according to official data, today the risk of fetal death increases by 15%, provided that the mother is in constant contact with sources of electromagnetic radiation. In addition to stillbirth, the likelihood of developing pathologies in an unborn child increases, slowing down in development, premature birth, miscarriage. Such is the impact of electromagnetic radiation on human health and future generations.

In addition to the huge negative effect of electromagnetic radiation on the human body, these waves can poison environment. The most susceptible areas include areas with a large accumulation of high-frequency power lines. Often they are located far from residential buildings, however, in individual cases, there is the presence of such power lines near settlements.

The flora and fauna are also exposed to the negative effects of harmful rays. In turn, a person eats irradiated animals and foodstuffs and, as a result, receives an additional dose of radiation-infected particles into his body. Such a process is extremely difficult to control due to factors beyond human control, but it is still possible to influence it.

Video: invisible enemy - electromagnetic radiation.

Data

To understand what constitutes the effect of electromagnetic fields on the human body, it is enough to familiarize yourself with the following facts:

1. Changes in the blood and urine of a 9-year-old child 15 minutes after sitting at the computer coincide with changes in the analyzes of a cancer patient. Teenagers are subject to similar influence after half an hour of being near the computer. And an adult undergoes a change in the analyzes after 2 hours.
2. The signal coming from a portable radiotelephone is able to penetrate the brain at a distance of up to 37.5 mm.
3. Electricians are 13 times more likely to develop brain cancer than other professions. The level of the magnetic field in such workers is practically destroyed.
4. A 13-year-old child who talks on the phone for about 2 minutes undergoes a bioelectrical brain change that takes place several hours after the conversation.
5. Animals, even slightly irradiated with a dose of electromagnetic radiation, began to lag behind in development, acquired pathologies in the body, as with radiation.

The electromagnetic emission standards have the following meanings:

• Radio waves - ultrashort (0.1mm-1m/30MHz-300GHz), short (10-100m/3MHz-30MHz), medium (100m-1km/300kHz-3MHz), long (1km-10km/30kHz-300kHz), extra long (more than 10 km / less than 30 kHz).
• Optical radiation - ultraviolet (380-10nm/7.5*10V 14stHz-3*10V 16stHz), visible radiation (780-380nm/429THz-750THz), infrared radiation (1mm-780nm/300GHz-429THz) .
• Ionizing electromagnetic radiation - X-ray, gamma. A more detailed table of calculations of EMP norms includes additional sources of propagation of harmful waves.

It is not possible to completely protect yourself from the effects of harmful waves. However, today there are a number of factors that can prevent the excessive influence of electromagnetic radiation on the human body:

1. Acquisition of a special dosimeter. Such a detector will help to calculate the most dangerous sources of radiation by calculating the frequency of their waves and, as a result, reduce the time spent near such sources or eliminate them completely. Devices for measuring electromagnetic fields are available at any household store.
2. Separation of radiation sources by area. It is not recommended to operate electromagnetic devices in a close radius between each other, otherwise their negative impact on the environment and the human body increases, causing maximum harm.
3. Isolation of radiation sources. We are talking, for example, about the refrigerator. It is advisable to use it at a distance from the dining table. A similar situation with a computer or laptop: the distance to the place of deployment (sofa, bed) should be at least one and a half meters.
4. Exclusion of toys with EMP. The electromagnetic effect of radio-controlled and electrical attributes for a children's room poses a serious threat to the health of an adult, and is extremely destructive for children. It is recommended to rid the room of EMP-radiated toys.
5. Radiotelephone isolation. This technique is capable of emitting harmful waves to a radius of up to 10 meters. It is extremely important to remove such electronics as far as possible. This method of protection will protect against the main source of harmful radiation, since the radiotelephone operates 24 hours a day.
6. Avoid buying counterfeit phones. The low price of such goods is due to the harmful radiation of electromagnetic waves per person in the first place.
7. Careful selection of household appliances. In this case, we are talking directly about devices with a steel case.

In addition to the above factors, there are well-known simple methods of protection against electromagnetic radiation, the observance of which will also allow you to protect yourself from EMR, reducing the risk of exposure to the lowest indicator:

• It is not recommended to be near a working microwave oven, as its waves have an extremely negative impact on the environment, in comparison Appliances.
• It is undesirable to be too close to the monitor.
• Excluded being close to high-frequency power lines.
• It is recommended to avoid an increased amount of jewelry on the body, which is desirable to remove before going to bed.
• Approved the presence of electrical appliances, analog household appliances, appliances and wiring at a distance of 2 meters from the bed.
• A minimum amount of time near working electrical appliances and similar equipment is recommended.
• It is undesirable to find idle devices in the on state.

Often, people do not attach much importance to the harm that electromagnetic radiation can cause the most common household appliances and other factors surrounding them, because they are not able to see their waves. This feature makes EMR extremely dangerous for the life of all living things.

Having the ability to accumulate in the body, harmful rays affect the vital systems, manifesting themselves in a variety of diseases and ailments. The full scale of this problem will be seen by humanity a generation later - only then will a specific impact on the health of those who happened to live their lives surrounded by EMP sources be indicated.

Electromagnetic radiation (EMR) accompanies modern man everywhere. Any technique whose action is based on electricity emits waves of energy. Some varieties of such radiation are constantly talked about - these are radiation, ultraviolet and, the danger of which has long been known to everyone. But about the impact of electromagnetic fields on the human body, if it occurs due to a working TV or smartphone, people try not to think about it.

Types of electromagnetic radiation

Before describing the danger of a particular type of radiation, it is necessary to understand what it is all about. School course Physics tells us that energy travels in the form of waves. Depending on their frequency and length, a large number of types of radiation are distinguished. So electromagnetic waves are:

1. high frequency radiation. It includes x-rays and gamma rays. They are also known as ionizing radiation.
2. Medium frequency radiation. This is the visible spectrum that humans perceive as light. In the upper and lower frequency scale are ultraviolet and infrared radiation.
3. low frequency radiation. It includes radio and microwaves.

To explain the effect of electromagnetic radiation on the human body, all these types are divided into 2 large categories - ionizing and non-ionizing radiation. The difference between them is quite simple:

• Ionizing radiation affects the atomic structure of matter. Because of this, biological organisms the structure of cells is disturbed, DNA is modified and tumors appear.
• Non-ionizing radiation has long been considered harmless. But recent studies by scientists show that with high power and prolonged exposure, it is no less dangerous to health.

Sources of EMP

Non-ionizing electromagnetic fields and radiation surround a person everywhere. They are emitted by any electronic equipment. In addition, we must not forget about the power lines, through which the most powerful charges of electricity pass. EMR is also emitted by transformers, elevators and other technical devices that provide comfortable conditions life.

Thus, it is enough to turn on the TV or talk on the phone so that the sources of electromagnetic radiation begin to affect the body. Even such a seemingly safe thing as an electronic alarm clock can affect health over time.

EMI measuring devices

To determine how strongly this or that source of electromagnetic radiation affects the body, devices for measuring electromagnetic fields are used. The simplest and most widely known is an indicator screwdriver. The LED at its end burns brighter with a powerful radiation source.

There are also professional devices - fluxmeters. Such an electromagnetic radiation detector is able to determine the power of the source and give its numerical characteristics. They can then be written to a computer and processed using various examples measured quantities and frequencies.

For humans, according to the norms of the Russian Federation, an EMR dose of 0.2 μT is considered safe.

More accurate and detailed tables are presented in GOSTs and SanPiNs. You can find formulas in them, thanks to which you can calculate how dangerous an EMP source is and how to measure electromagnetic radiation, depending on the location of the equipment and the size of the room.

If radiation is measured in R / h (the number of roentgens per hour), then EMR is measured in V / m 2 (volts per meter square square). The following indicators are considered a safe norm for a person, depending on the frequency of the wave, measured in hertz:

• up to 300 kHz - 25 V / m 2;
• 3 MHz - 15 V / m 2;
• 30 MHz - 10 V / m 2;
• 300 MHz - 3 V / m 2;
• Above 0.3 GHz - 10 μV / cm 2.

It is thanks to the measurements of these indicators that the safety for a person of a particular source of EMR is determined.

How does electromagnetic radiation affect a person?

Given that many people have been in constant contact with electrical appliances since childhood, there is legitimate question: Is EMP so dangerous? Unlike radiation, it does not lead to radiation sickness and its effect is imperceptible. And is it worth observing the norms of electromagnetic radiation?

Scientists also asked this question back in the 60s of the 20th century. More than 50 years of research have shown that the human electromagnetic field is modified under the influence of other radiations. This leads to the development of the so-called radio wave sickness».

Spurious electromagnetic radiation and pickup disrupt the work of many organ systems. But the most sensitive to their effects are nervous and cardiovascular.

According to statistics recent years, about a third of the population is affected by radio wave sickness. It manifests itself through symptoms familiar to many:

• depression;
• chronic fatigue;
• insomnia;
• headache;
• concentration disorders;
• dizziness.

At the same time, the negative impact of electromagnetic radiation on human health is most dangerous because doctors still cannot diagnose it. After examination and testing, the patient goes home with a diagnosis: “Healthy!”. At the same time, if nothing is done, the disease will develop and pass into the chronic stage.

Each of the organ systems will respond to electromagnetic effects in different ways. The central nervous system is most sensitive to the effects of electromagnetic fields on humans.

EMI impairs signal transmission through the neurons of the brain. As a result, it affects the activity of the organism as a whole.

Also, over time, negative consequences for the psyche appear - attention and memory are disturbed, and in the worst cases, problems transform into delirium, hallucinations and suicidal tendencies.

The influence of electromagnetic waves on living organisms has a large-scale impact and through circulatory system.

Erythrocytes, platelets and other bodies have their own potentials. Under the influence of electromagnetic radiation on a person, they can stick together. As a result, there is a blockage of blood vessels and the performance of the transport function of the blood worsens.

EMR also reduces the permeability of cell membranes. As a result, all tissues exposed to radiation do not receive the necessary oxygen and nutrients. In addition, the efficiency of hematopoietic functions decreases. The heart, in turn, responds to this problem with arrhythmia and a drop in myocardial conduction.

The influence of electromagnetic waves on the human body destroys the immune system. Due to the clumping of blood cells, lymphocytes and leukocytes are blocked. Accordingly, the infection simply does not meet with resistance from defense systems. As a result, not only the frequency of colds increases, but also an exacerbation of chronic ailments.

Another consequence of harm from electromagnetic radiation is the disruption of hormone production. Impact on the brain and circulatory system stimulates the pituitary gland, adrenal glands and other glands.

The reproductive system is also sensitive to electromagnetic radiation, the impact on a person can be catastrophic. Given the disruption of hormone production, men's potency decreases. But for women, the consequences are more serious - during the first trimester of pregnancy, a strong dose of radiation can lead to a miscarriage. And if this does not happen, then the disturbance of the electromagnetic field can disrupt the normal process of cell division, damaging DNA. The result is pathological development of children.

The effect of electromagnetic fields on the human body is destructive, which is confirmed by numerous studies.

Considering that modern medicine has practically nothing to oppose to radio wave disease, you must try to protect yourself on your own.

EMP protection

Given the whole possible harm, which brings the influence of the electromagnetic field to living organisms, simple and reliable safety rules have been developed. In enterprises in which a person is constantly faced with high levels EMP, special protective screens and equipment are provided for workers.

But at home, the sources of the electromagnetic field cannot be screened like that. At the very least, this will be inconvenient. Therefore, you should understand how to protect yourself in other ways. In total, there are 3 rules that must be observed constantly in order to reduce the impact of the electromagnetic field on human health:

1. Stay as far away from EMP sources as possible. For power lines, 25 meters is enough. And the screen of a monitor or TV is dangerous if it is located closer than 30 cm. It is enough to carry smartphones and tablets not in pockets, but in handbags or purses 3 cm from the body.
2. Reduce contact time with EMP. This means that you do not have to stand for a long time near the working sources of the electromagnetic field. Even if you want to follow the cooking on an electric stove or warm up by the heater.
3. Turn off unused electrical appliances. This will not only reduce the level of electromagnetic radiation, but also help save money on your energy bills.

You can also take a set of preventive measures so that the impact of electromagnetic waves is minimal. For example, having measured the radiation power of various devices with a dosimeter, it is necessary to record the EMF readings. The emitters can then be distributed around the room to reduce the load on individual areas of the area. It is also important to consider that the steel case shields EMP well.

Do not forget that electromagnetic radiation radio frequency range from means of communication constantly influence the fields of a person, as long as these devices are turned on. Therefore, before going to bed and during work, it is better to put them away.

The content of the article

ELECTROMAGNETIC RADIATION, electromagnetic waves excited by various radiating objects - charged particles, atoms, molecules, antennas, etc. Depending on the wavelength, gamma radiation, x-rays, ultraviolet radiation, visible light, infrared radiation, radio waves and low-frequency electromagnetic oscillations are distinguished.

It may seem surprising that outwardly so different physical phenomena have common ground. Indeed, what is there in common between a piece of radioactive material, an X-ray tube, a mercury discharge lamp, a flashlight bulb, a warm stove, a radio broadcasting station, and an alternating current generator connected to a power line? As, however, between the film, the eye, the thermocouple, the television antenna and the radio receiver. However, the first list consists of sources, and the second - of receivers of electromagnetic radiation. The effects of different types of radiation on the human body are also different: gamma and x-ray radiation penetrate it, causing tissue damage, visible light causes a visual sensation in the eye, infrared radiation, falling on the human body, heats it up, and radio waves and low-frequency electromagnetic oscillations by the human body and are not felt at all. Despite these obvious differences, all these types of radiation are, in essence, different aspects of the same phenomenon.

The interaction between the source and the receiver formally consists in the fact that with any change in the source, for example, when it is turned on, there is some change in the receiver. This change does not occur immediately, but after some time, and is quantitatively consistent with the idea that something moves from the source to the receiver at a very high speed. Sophisticated mathematical theory and a huge variety of experimental data show that the electromagnetic interaction between a source and a receiver separated by a vacuum or a rarefied gas can be represented as waves propagating from the source to the receiver at the speed of light With.

The speed of propagation in free space is the same for all types of electromagnetic waves from gamma rays to low-frequency waves. But the number of oscillations per unit time (i.e. frequency f) varies over a very wide range: from a few oscillations per second for low-frequency electromagnetic waves to 10 20 oscillations per second in the case of x-rays and gamma radiation. Since the wavelength (i.e. the distance between adjacent wave peaks; Fig. 1) is given by l = c/f, it also varies over a wide range - from several thousand kilometers for low-frequency oscillations to 10–14 m for X-ray and gamma radiation. That is why the interaction of electromagnetic waves with matter is so different in different parts of their spectrum. And yet all these waves are related to each other, as are related water ripples, waves on the surface of a pond and stormy ocean waves, which also affect objects in their path in different ways. Electromagnetic waves differ significantly from waves on water and from sound in that they can be transmitted from a source to a receiver through vacuum or interstellar space. For example, X-rays generated in a vacuum tube affect a photographic film located far from it, while the sound of a bell located under a hood cannot be heard if air is pumped out from under the hood. The eye perceives the rays of visible light coming from the Sun, and the antenna located on the Earth perceives radio signals remote for millions of kilometers. spacecraft. Thus, no material medium, such as water or air, is required for the propagation of electromagnetic waves.

Sources of electromagnetic radiation.

Despite the physical differences, in all sources of electromagnetic radiation, whether it be a radioactive substance, an incandescent lamp or a television transmitter, this radiation is excited by electric charges moving with acceleration. There are two main types of sources. In "microscopic" sources, charged particles jump from one energy level to another within atoms or molecules. Radiators of this type emit gamma, x-ray, ultraviolet, visible and infrared, and in some cases even longer wavelength radiation (an example of the latter is the line in the hydrogen spectrum corresponding to a wavelength of 21 cm, which plays an important role in radio astronomy). Sources of the second type can be called macroscopic. In them, the free electrons of the conductors perform synchronous periodic fluctuations. The electrical system can have a wide variety of configurations and sizes. Systems of this type generate radiation in the range from millimeter to the longest waves (in power lines).

Gamma rays are emitted spontaneously during the decay of atomic nuclei radioactive substances such as radium. In this case, complex processes of changes in the structure of the nucleus occur, associated with the movement of charges. Generated frequency f determined by the energy difference E 1 and E 2 two states of the kernel: f=(E 1 – E 2)/h, where h is Planck's constant.

X-ray radiation occurs when the surface of a metal anode (anticathode) is bombarded in vacuum with high-velocity electrons. Rapidly slowing down in the anode material, these electrons emit the so-called bremsstrahlung, which has a continuous spectrum, and the rearrangement of the internal structure of the anode atoms, which occurs as a result of electron bombardment, as a result of which the atomic electrons pass into a state with a lower energy, is accompanied by the emission of the so-called characteristic radiation, frequency which are determined by the anode material.

The same electronic transitions in the atom give ultraviolet and visible light radiation. As for infrared radiation, it is usually the result of changes that have little effect on the electronic structure and are associated mainly with changes in the amplitude of oscillations and torque momentum of the molecule.

In the generators of electrical oscillations there is an "oscillatory circuit" of one type or another, in which the electrons perform forced oscillations with a frequency depending on its design and size. The highest frequencies corresponding to millimeter and centimeter waves are generated by klystrons and magnetrons - vacuum devices with metal cavity resonators, oscillations in which are excited by electron currents. In generators of lower frequencies, the oscillatory circuit consists of an inductor (inductance L) and a capacitor (capacitance C) and is excited by a tube or transistor circuit. The natural frequency of such a circuit, which is close to resonant at low damping, is given by .

The very low frequency alternating fields used for the transmission of electrical energy are created by electric machine current generators in which rotors carrying wire windings rotate between the poles of magnets.

Maxwell's theory, ether and electromagnetic interaction.

When an ocean liner passes at some distance from a fishing boat in calm weather, after a while the boat begins to sway violently in the waves. The reason for this is clear to everyone: from the nose of the liner, a wave runs along the surface of the water in the form of a sequence of humps and depressions, which reaches the fishing boat.

When using a special generator installed on artificial satellite The earth and the antenna directed to the Earth are excited by electric charge oscillations, in the receiving antenna on the Earth (also after some time) an electric current is excited. How is the interaction transmitted from the source to the receiver if there is no material medium between them? And if the signal arriving at the receiver can be represented as some kind of incident wave, then what kind of wave is it that can propagate in a vacuum, and how can humps and depressions appear where there is nothing?

Scientists have been thinking about these questions in relation to visible light propagating from the Sun to the eye of the observer for a long time. For most of the 19th century physicists such as O. Fresnel, I. Fraunhofer, F. Neumann tried to find the answer in the fact that space is actually not empty, but filled with a certain medium (“luminiferous ether”), endowed with the properties of an elastic solid body. Although such a hypothesis helped to explain some phenomena in a vacuum, it led to insurmountable difficulties in the problem of the passage of light through the boundary of two media, such as air and glass. This prompted the Irish physicist J. McCullagh to reject the idea of ​​an elastic ether. In 1839 he suggested new theory, in which the existence of a medium was postulated, in its properties different from all known materials. Such a medium does not resist compression and shear, but resists rotation. Because of these strange properties, McCullagh's ether model did not initially attract much interest. However, in 1847 Kelvin demonstrated the existence of an analogy between electrical phenomena and mechanical elasticity. Proceeding from this, as well as from M. Faraday's ideas about the lines of force of electric and magnetic fields, J. Maxwell proposed a theory of electrical phenomena, which, in his words, “denies action at a distance and attributes electric action to voltages and pressures in some all-pervading medium, moreover, these voltages are the same as those with which engineers deal, and the medium is precisely the medium in which light is supposed to propagate. In 1864 Maxwell formulated a system of equations covering all electromagnetic phenomena. It is noteworthy that his theory in many ways resembled the theory proposed a quarter of a century earlier by McCullagh. Maxwell's equations were so comprehensive that they derived the laws of Coulomb, Ampère, electromagnetic induction and followed the conclusion about the coincidence of the speed of propagation of electromagnetic phenomena with the speed of light.

After Maxwell's equations were given more simple form(mainly due to O. Heaviside and G. Hertz), field equations became the core of electromagnetic theory. Although these equations themselves did not require a Maxwellian interpretation based on ideas about stresses and pressures in the ether, such an interpretation was universally accepted. The undoubted success of the equations in predicting and explaining various electromagnetic phenomena was taken as confirmation of the validity of not only the equations, but also the mechanistic model on the basis of which they were derived and interpreted, although this model was completely unimportant for mathematical theory. Faraday lines of force fields and tubes of current, along with deformations and displacements, have become essential attributes of the ether. Energy was considered as stored in a stressed medium, and G. Poynting in 1884 presented its flow as a vector, which now bears his name. In 1887 Hertz experimentally demonstrated the existence of electromagnetic waves. In a series of brilliant experiments, he measured the speed of their propagation, and also showed that they can be reflected, refracted and polarized. In 1896, G. Marconi received a patent for radio communications.

In continental Europe, independently of Maxwell, the theory of long-range action was developed - a completely different approach to the problem of electromagnetic interaction. Maxwell wrote about this: “According to the theory of electricity, which is making great progress in Germany, two charged particles directly act on each other at a distance with a force which, according to Weber, depends on their relative speed and acts, according to a theory based on ideas Gauss and developed by Riemann, Lorentz and Neumann, not instantly, but after some time, depending on the distance. To appreciate the power of this theory, which is so outstanding people explains any kind of electrical phenomena, can only be studied by studying it. The theory that Maxwell spoke about was most fully developed by the Danish physicist L. Lorentz with the help of scalar and vector retarded potentials, almost the same as in modern theory. Maxwell rejected the idea of ​​delayed action at a distance, be it potentials or forces. “These physical hypotheses are completely alien to my ideas about the nature of things,” he wrote. However, the theory of Riemann and Lorentz was mathematically identical to his theory, and in the end he agreed that there was more convincing evidence in favor of the long-range theory. In his Treatise on electricity and magnetism (Treatise on Electricity and Magnetism, 1873) he wrote: “It should not be overlooked that we have taken only one step in the theory of the action of the medium. We suggested that it is in a state of tension, but did not explain at all what kind of voltage it is and how it is maintained.

In 1895, the Dutch physicist H. Lorenz combined the early limited theories of the interaction between fixed charges and currents, which anticipated the theory of retarded potentials by L. Lorentz and were created mainly by Weber, with Maxwell's general theory. H.Lorentz considered matter as containing electric charges, which, interacting with each other in various ways, produce all known electromagnetic phenomena. Instead of accepting the concept of retarded action at a distance, described by the retarded potentials of Riemann and L. Lorentz, he proceeded from the assumption that the movement of charges creates an electromagnetic field, capable of propagating through the ether and transferring momentum and energy from one system of charges to another. But is it necessary for the propagation of an electromagnetic field in the form of an electromagnetic wave the existence of such a medium as the ether? Numerous experiments designed to confirm the existence of the ether, including the "ether entrainment" experiment, gave a negative result. Moreover, the hypothesis of the existence of the ether turned out to be in conflict with the theory of relativity and with the position of the constancy of the speed of light. The conclusion can be illustrated by the words of A. Einstein: "If the ether is not characterized by any specific state of motion, then it hardly makes sense to introduce it as a kind of entity of a special kind along with space."

Emission and propagation of electromagnetic waves.

Electric charges moving with acceleration and periodically changing currents act on each other with some forces. The magnitude and direction of these forces depend on such factors as the configuration and size of the region containing the charges and currents, the magnitude and relative direction of the currents, the electrical properties of the medium, and changes in the concentration of charges and the distribution of source currents. Due to the complexity of the general formulation of the problem, the law of forces cannot be represented as a single formula. The structure, called the electromagnetic field, which, if desired, can be considered as a purely mathematical object, is determined by the distribution of currents and charges created by a given source, taking into account the boundary conditions determined by the shape of the interaction region and the properties of the material. When it comes to unlimited space, these conditions are supplemented by a special boundary condition - radiation condition. The latter guarantees the "correct" behavior of the field at infinity.

The electromagnetic field is characterized by the strength vector electric field E and magnetic induction vector B, each of which at any point in space has a certain magnitude and direction. On fig. 2 schematically shows an electromagnetic wave with vectors E and B, propagating in the positive direction of the axis X. The electric and magnetic fields are closely interconnected: they are components of a single electromagnetic field, since they transform into each other under Lorentz transformations. A vector field is said to be linearly (flat) polarized if the direction of the vector remains fixed everywhere and its length changes periodically. If the vector rotates, but its length does not change, then the field is said to have circular polarization; if the length of the vector changes periodically, and it rotates, then the field is called elliptically polarized.

The relationship between the electromagnetic field and the oscillating currents and charges that maintain this field can be illustrated by a relatively simple, but very clear example of an antenna like a half-wave dipole (Fig. 3). If a thin wire, the length of which is half the wavelength of the radiation, is cut in the middle and a high-frequency generator is connected to the cut, then the applied alternating voltage will maintain an approximately sinusoidal current distribution in the vibrator. At the point in time t= 0 when the current amplitude reaches maximum value, and the velocity vector of positive charges is directed upwards (negative - downwards), at any point of the antenna, the charge per unit of its length is equal to zero. After the first quarter of the period ( t =T/4) positive charges will be concentrated on the upper half of the antenna, and negative charges on the bottom. In this case, the current is zero (Fig. 3, b). In the moment t = T/2 the charge per unit length is zero, and the velocity vector of positive charges is directed downward (Fig. 3, in). Then, by the end of the third quarter, the charges are redistributed (Fig. 3, G), and upon its completion, the full period of oscillations ends ( t = T) and everything looks like in Fig. 3, a.

In order for a signal (for example, a time-varying current that drives the loudspeaker of a radio receiver) to be transmitted over a distance, the radiation of the transmitter must be modulate by, for example, changing the amplitude of the current in the transmitting antenna in accordance with the signal, which will entail modulation of the amplitude of the oscillations of the electromagnetic field (Fig. 4).

The transmitting antenna is that part of the transmitter where electric charges and currents oscillate, radiating an electromagnetic field into the surrounding space. The antenna can have a wide variety of configurations, depending on what form of electromagnetic field you want to get. It can be a single symmetrical vibrator or a system of symmetrical vibrators located at a certain distance from each other and providing the necessary ratio between the amplitudes and phases of the currents. The antenna may be a symmetrical vibrator located in front of a relatively large flat or curved metal surface that acts as a reflector. In the range of centimeter and millimeter waves, an antenna in the form of a horn connected to a metal pipe-waveguide, which plays the role of a transmission line, is especially effective. Currents in the short antenna at the input of the waveguide induce alternating currents on its inner surface. These currents and the associated electromagnetic field propagate along the waveguide to the horn.

By changing the design of the antenna and its geometry, it is possible to achieve such a ratio of the amplitudes and phases of current oscillations in its various parts so that the radiation is amplified in some directions and attenuated in others (directional antennas).

At large distances from any type of antenna, the electromagnetic field has a rather simple form: at any given point, the electric field strength vectors E and magnetic field induction AT oscillate in phase in mutually perpendicular planes, decreasing in inverse proportion to the distance from the source. In this case, the wave front has the form of an increasing sphere, and the energy flux vector (the Poynting vector) is directed outward along its radii. The integral of the Poynting vector over the entire sphere gives the total time-averaged radiated energy. In this case, waves propagating in the radial direction at the speed of light carry from the source not only oscillations of vectors E and B, but also the momentum of the field and its energy.

Reception of electromagnetic waves and scattering phenomenon.

If a conducting cylinder is placed in the zone of an electromagnetic field propagating from a remote source, then the currents induced in it will be proportional to the strength of the electromagnetic field and, in addition, will depend on the orientation of the cylinder relative to the incident wave front and on the direction of the electric field strength vector. If the cylinder is in the form of a wire whose diameter is small compared to the wavelength, then the induced current will be maximum when the wire is parallel to the vector E falling wave. If the wire is cut in the middle and a load is connected to the resulting terminals, then energy will be supplied to it, as is the case in the case of a radio receiver. The currents in this wire behave in the same way as the alternating currents in the transmitting antenna, and therefore it also radiates a field into the surrounding space (i.e., the incident wave is scattered).

Reflection and refraction of electromagnetic waves.

The transmitting antenna is usually mounted high above the ground. If the antenna is in dry sandy or rocky terrain, then the ground behaves like an insulator (dielectric), and the currents induced in it by the antenna are associated with intra-atomic vibrations, since there are no free charge carriers here, as in conductors and ionized gases. These microscopic oscillations create above the earth's surface a field reflected from the earth's surface of an electromagnetic wave and, in addition, change the direction of propagation of the wave entering the soil. This wave moves at a lower speed and at a smaller angle to the normal than the incident one. This phenomenon is called refraction. If the wave falls on a portion of the earth's surface, which, along with dielectric, also has conductive properties, then the overall picture for the refracted wave looks much more complicated. As before, the wave changes direction at the interface, but now the field in the ground propagates in such a way that the surfaces of equal phases no longer coincide with the surfaces of equal amplitudes, as is usually the case in the case of a plane wave. In addition, the amplitude of wave oscillations rapidly decays, since conduction electrons give up their energy to atoms during collisions. As a result, the energy of wave oscillations transforms into the energy of chaotic thermal motion and dissipates. Therefore, where the ground conducts electricity, waves cannot penetrate it to a great depth. The same applies to sea ​​water which makes radio communication with submarines difficult.

In the upper layers earth's atmosphere There is a layer of ionized gas called the ionosphere. It consists of free electrons and positively charged ions. Under the influence of electromagnetic waves sent from the earth, the charged particles of the ionosphere begin to oscillate and radiate their own electromagnetic field. Charged ionospheric particles interact with the sent wave in approximately the same way as dielectric particles in the case considered above. However, the electrons of the ionosphere are not bound to atoms, as in a dielectric. They react to electric field of the sent wave is not instantaneous, but with some phase shift. As a result, the wave in the ionosphere propagates not at a smaller, as in a dielectric, but at a greater angle to the normal than the incident wave sent from the earth, and the phase velocity of the wave in the ionosphere turns out to be greater than the speed of light c. When the wave falls at a certain critical angle, the angle between the refracted ray and the normal becomes close to a straight line, and with a further increase in the angle of incidence, the radiation is reflected towards the Earth. Obviously, in this case, the electrons of the ionosphere create a field that compensates for the field of the refracted wave in the vertical direction, and the ionosphere acts as a mirror.

Energy and momentum of radiation.

In modern physics, the choice between Maxwell's theory of the electromagnetic field and the theory of delayed long-range action is made in favor of Maxwell's theory. As long as we are only interested in the interaction between source and receiver, both theories are equally good. However, the theory of long-range action does not give any answer to the question of where is the energy that has already been emitted by the source, but has not yet been received by the receiver. According to Maxwell's theory, the source transfers energy to the electromagnetic wave, in which it is located, until it is transferred to the receiver that absorbed the wave. At the same time, the law of conservation of energy is observed at each stage.

Thus, electromagnetic waves have energy (as well as momentum), which makes us consider them as real as, for example, atoms. Electrons and protons located in the Sun transfer energy to electromagnetic radiation, mainly in the infrared, visible and ultraviolet regions of the spectrum; After about 500 seconds, having reached the Earth, it releases this energy: the temperature rises, photosynthesis occurs in the green leaves of plants, and so on. In 1901, P.N. Lebedev experimentally measured the pressure of light, confirming that light has not only energy, but also momentum (moreover, the relationship between them is consistent with Maxwell's theory).

Photons and quantum theory.

At the turn of the 19th and 20th centuries, when it seemed that an exhaustive theory of electromagnetic radiation had finally been built, nature presented another surprise: it turned out that in addition to wave properties, described by Maxwell's theory, the radiation also exhibits the properties of particles, and the stronger, the shorter the wavelength. These properties are especially pronounced in the phenomenon of the photoelectric effect (knocking out electrons from the surface of a metal under the action of light), discovered in 1887 by G. Hertz. It turned out that the energy of each ejected electron depends on the frequency n incident light, but not on its intensity. This indicates that the energy associated with the light wave is transmitted in discrete portions - quanta. If the intensity of the incident light is increased, then the number of electrons knocked out per unit time increases, but not the energy of each of them. In other words, radiation transmits energy in certain minimal portions - like particles of light, which were called photons. A photon has neither rest mass nor charge, but has spin and momentum equal to hn/c, and energy equal to hn; it moves in free space at a constant speed c.

How can electromagnetic radiation have all the properties of waves, manifested in interference and diffraction, but behave like a stream of particles in the case of the photoelectric effect? At present, the most satisfactory explanation of this duality can be found in the complicated formalism of quantum electrodynamics. But even this sophisticated theory has its difficulties, and its mathematical consistency is questionable. PARTICLES ELEMENTARY; PHOTOELECTRIC EFFECT; QUANTUM MECHANICS; VECTOR.

Fortunately, in macroscopic problems of emitting and receiving millimeter and longer electromagnetic waves, quantum mechanical effects usually do not play a significant role. The number of photons emitted, for example, by a symmetric dipole antenna, is so large, and the energy carried by each of them is so small that one can forget about discrete quanta and assume that the emission of radiation is a continuous process.

An electromagnetic pulse (EMP) is a natural phenomenon caused by the rapid acceleration of particles (mainly electrons), which results in an intense burst electromagnetic energy. Everyday examples of EMP are lightning, combustion engine ignition systems, and solar flares. Although electromagnetic pulse able to disable electronic devices, this technology can be used to purposefully and safely disable electronic devices or to ensure the security of personal and confidential data.

Steps

Creation of an elementary electromagnetic emitter

Gather the required materials. To create a simple electromagnetic emitter, you will need a disposable camera, copper wire, rubber gloves, solder, a soldering iron and an iron rod. All of these items can be purchased at your local hardware store.

• The thicker the wire you take for the experiment, the more powerful the final emitter will be.
• If you can't find an iron bar, you can replace it with a non-metal rod. However, please note that such a replacement will adversely affect the power of the pulse produced.
• When handling electrical parts capable of holding a charge, or when passing an electrical current through an object, we strongly recommend that you wear rubber gloves to avoid possible electrical shock.

1. Assemble the electromagnetic coil. An electromagnetic coil is a device that consists of two separate, but at the same time interconnected parts: a conductor and a core. In this case, an iron rod will act as a core, and a copper wire will act as a conductor.

   Solder the ends of the electromagnetic coil to the capacitor. The capacitor is usually a cylinder with two terminals and can be found on any circuit board. In a disposable camera, such a capacitor is responsible for the flash. Before soldering the capacitor, be sure to remove the battery from the camera, otherwise you may be shocked.

   Find a safe place to test your electromagnetic emitter. Depending on the materials involved, the effective range of your EMP will be approximately one meter in any direction. Be that as it may, any electronics that fall under the EMP will be destroyed.

   • Do not forget that EMP affects all devices without exception in the radius of destruction, ranging from life support devices, such as pacemakers, and ending with mobile phones. Any damage caused by this device through EMP may result in legal consequences.
   • A grounded area, such as a tree stump or a plastic table, is an ideal surface for testing an electromagnetic emitter.

2. Find a suitable test object. Since the electromagnetic field only affects electronics, consider purchasing some inexpensive device from your local electronics store. The experiment can be considered successful if, after the activation of the EMR, the electronic device stops working.

   • Many office supply stores sell fairly inexpensive electronic calculators with which you can check the effectiveness of the created emitter.

3. Insert the battery back into the camera. To restore the charge, you need to pass electricity through the capacitor, which will subsequently provide your electromagnetic coil with current and create an electromagnetic pulse. Place the test object as close as possible to the EM emitter.

   Let the capacitor charge. Let the battery charge the capacitor again by disconnecting it from the electromagnetic coil, then reconnect them with rubber gloves or plastic tongs. When working with bare hands, you risk getting an electric shock.

   Turn on the capacitor. Activating the flash on the camera will release the electricity stored in the capacitor, which, when passed through the coil, will create an electromagnetic pulse.

   Creation of a portable EM radiation device

   1. Gather everything you need. Creating a portable EMP device will go much more smoothly if you have all the necessary tools and components. You will need the following items:

      Pull the circuit board out of the camera. Inside the disposable camera is a circuit board, which is responsible for its functionality. First, remove the batteries, and then the board itself, not forgetting to note the position of the capacitor.

      • When working with the camera and the condenser while wearing rubber gloves, you thereby protect yourself from possible electric shock.
      • Capacitors are usually in the form of a cylinder with two pins attached to the board. This is one of the most important details of the future EMP device.
      • After you remove the battery, click the camera a couple of times to use up the accumulated charge in the capacitor. Due to the accumulated charge, you can be electrocuted at any time.

   2. Wind the copper wire around the iron core. Take enough copper wire so that evenly running turns can completely cover the iron core. Also make sure that the turns fit snugly together, otherwise this will negatively affect the power of the EMP.

      • Leave a small amount of wire at the ends of the winding. They are needed to connect the rest of the device to the coil.

   3. Apply insulation to the radio antenna. The radio antenna will serve as a handle on which the coil and the board from the camera will be fixed. Wrap electrical tape around the base of the antenna to protect against electric shock.

      Attach the board to a thick piece of cardboard. The cardboard will serve as another layer of insulation that will save you from a nasty electrical discharge. Take the board and fix it with electrical tape on the cardboard, but so that it does not cover the tracks of the electrically conductive circuit.

      • Fasten the board face up so that the capacitor and its conductive traces do not come into contact with the cardboard.
      • The cardboard backing for the PCB should also have enough space for the battery compartment.

   4. Attach the electromagnetic coil to the end of the radio antenna. Since electrical current must pass through the coil to create EMP, it's a good idea to add a second layer of insulation by placing a small piece of cardboard between the coil and the antenna. Take some duct tape and attach the spool to a piece of cardboard.

      Solder the power supply. Locate the battery connectors on the board and connect them to the corresponding contacts in the battery compartment. After that, you can fix the whole thing with electrical tape on a free area of ​​\u200b\u200bthe cardboard.

      Connect the coil to the capacitor. You need to solder the ends of the copper wire to the electrodes of your capacitor. A switch should also be installed between the capacitor and the electromagnetic coil, which would control the flow of electricity between these two components.