Electrostatic field electrostatic field
electric field of stationary electric charges.
ELECTROSTATIC FIELDELECTROSTATIC FIELD, the electric field of stationary and unchanging electric charges over time, which interacts between them.
An electrostatic field is characterized by an electric field strength (cm. ELECTRIC FIELD VOLTAGE) E, which is its strength characteristic: Tension electrostatic field shows with what force the electrostatic field acts on a unit positive electric charge (cm. ELECTRIC CHARGE)placed at a given point in the field. The direction of the tension vector coincides with the direction of the force acting on the positive charge, and opposite to the direction of the force acting on the negative charge.
An electrostatic field is stationary (constant) if its strength does not change over time. Stationary electrostatic fields are created by stationary electric charges.
An electrostatic field is uniform if its intensity vector is the same at all points of the field, if the intensity vector at different points is different, the field is nonuniform. Homogeneous electrostatic fields are, for example, the electrostatic fields of a uniformly charged finite plane and a flat capacitor (cm. CONDENSER (electric)) away from the edges of its plates.
One of the fundamental properties of the electrostatic field is that the work of the forces of the electrostatic field when the charge moves from one point of the field to another does not depend on the trajectory of motion, but is determined only by the position of the starting and ending points and the magnitude of the charge. Consequently, the work of the forces of the electrostatic field when the charge moves along any closed trajectory is zero. Force fieldsthat have this property are called potential or conservative. That is, the electrostatic field is a potential field, the energy characteristic of which is the electrostatic potential (cm. ELECTROSTATIC POTENTIAL) associated with the vector of intensity E by the ratio:
E \u003d -gradj.
Force lines are used to graphically represent the electrostatic field. (cm. POWER LINES) (tension lines) - imaginary lines, tangents to which coincide with the direction of the intensity vector at each point of the field.
For electrostatic fields, the principle of superposition is observed (cm. SUPERPOSITION PRINCIPLE)... Each electric charge creates an electric field in space, regardless of the presence of other electric charges. The strength of the resulting field created by the system of charges is equal to the geometric sum of the strengths of the fields created at a given point by each of the charges separately.
Any charge in the surrounding space creates an electrostatic field. To detect a field at any point, it is necessary to place a point test charge at the observation point - a charge that does not distort the field under study (does not cause a redistribution of charges that create the field).
The field created by a solitary point charge q is spherically symmetric. Strength modulus of a solitary point charge in vacuum using Coulomb's law (cm. PENDANT LAW) can be represented as:
E \u003d q / 4pe about r 2.
Where e about - electrical constant, \u003d 8.85. 10 -12 F / m.
Coulomb's law, established using the torsion balance created by him (see Coulomb scales (cm. PENDANT LIBRA)), is one of the basic laws describing the electrostatic field. He establishes the relationship between the force of interaction of charges and the distance between them: the force of interaction of two point stationary charged bodies in a vacuum is directly proportional to the product of the moduli of charges and inversely proportional to the square of the distance between them.
This force is called Coulomb, and the field is called Coulomb. In a Coulomb field, the direction of the vector depends on the sign of the charge Q: if Q\u003e 0, then the vector is directed along the radius from the charge, if Q ( cm. DIELECTRIC PERMEABILITY) of the medium) is less than in a vacuum.
The experimentally established Coulomb's law and the principle of superposition make it possible to fully describe the electrostatic field of a given system of charges in a vacuum. However, the properties of the electrostatic field can be expressed in another, more general formwithout resorting to the concept of the Coulomb field of a point charge. The electric field can be characterized by the value of the flux of the electric field strength vector, which can be calculated in accordance with the Gauss theorem (cm. GAUSS'S THEOREM)... Gauss's theorem establishes a relationship between the flow of electric field strength through a closed surface and the charge inside this surface. The intensity flux depends on the distribution of the field over the surface of a particular area and is proportional to the electric charge inside this surface.
If an insulated conductor is placed in an electric field, then a force will act on the free charges q in the conductor. As a result, a short-term movement of free charges occurs in the conductor. This process will end when the intrinsic electric field of the charges that have arisen on the surface of the conductor completely compensates for the external field, i.e., an equilibrium distribution of charges is established, at which the electrostatic field inside the conductor turns to zero: at all points inside the conductor E \u003d 0, then there is no field. The lines of force of the electrostatic field outside the conductor in the immediate vicinity of its surface are perpendicular to the surface. If this were not so, then there would be a component of the field strength, current would flow along the surface of the conductor and over the surface. The charges are located only on the surface of the conductor, while all points on the surface of the conductor have the same potential value. The surface of the conductor is the equipotential surface (cm. EQUIPOTENTIAL SURFACE)... If there is a cavity in the conductor, then the electric field in it is also zero; the electrostatic protection of electrical devices is based on this.
If a dielectric is placed in an electrostatic field, then a polarization process occurs in it - the process of orientation of dipoles (cm. DIPOLE) or the appearance of dipoles oriented along the field under the influence of an electric field. In a homogeneous dielectric, the electrostatic field due to polarization (see Polarization of dielectrics) decreases in? time.
encyclopedic Dictionary. 2009 .
See what "electrostatic field" is in other dictionaries:
electrostatic field - Electric field of stationary charged bodies in the absence of electric currents in them. [GOST R 52002 2003] electrostatic field Electric field of stationary electric charges. The principles of the field in question are used to create ... ... Technical translator's guide
Electrostatic field - a set of phenomena associated with the emergence, conservation and relaxation of a free electric charge on the surface and volume of substances, materials, products. Source … Dictionary-reference book of terms of normative and technical documentation
Electrostatic field is a field created by electric charges that are stationary in space and constant in time (in the absence of electric currents). An electric field is a special type of matter associated with electric ... ... Wikipedia
Electric. field of motionless electrics. charges, carrying out the take-off between them. As well as perm. electric field, E. p. is characterized by the intensity of the electric. field K is the ratio of the force acting on the charge from the field to the value of the charge. Power ... Physical encyclopedia
The electric field of stationary electric charges ... Big Encyclopedic Dictionary
Electrostatic field - a set of phenomena associated with the emergence, preservation and relaxation of a free electric charge on the surface and volume of substances, materials, products ... Source: MSanPiN 001 96. Sanitary standards for permissible levels of physical factors ... Official terminology
electrostatic field - elektrostatinis laukas statusas T sritis Standartizacija ir metrologija apibrėžtis Apibrėžtį žr. priede. priedas (ai) Grafinis formatas atitikmenys: angl. electrostatic field vok. elektrostatisches Feld, n rus. electrostatic field, n pranc. ... ...
electrostatic field - elektrostatinis laukas statusas T sritis Standartizacija ir metrologija apibrėžtis Nejudančių elektringųjų dalelių elektrinis laukas. atitikmenys: angl. electrostatic field vok. elektrostatisches Feld, n rus. electrostatic field, n pranc. ... ... Penkiakalbis aiškinamasis metrologijos terminų žodynas
electrostatic field - elektrostatinis laukas statusas T sritis fizika atitikmenys: angl. electrostatic field vok. elektrostatisches Feld, n rus. electrostatic field, n pranc. champ électrostatique, m ... Fizikos terminų žodynas
The electric field of stationary electric charges, which interacts between them. Like an alternating electric field, an electric field is characterized by the strength of the electric field E: the ratio of the force acting on the charge to ... ... Great Soviet Encyclopedia
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- New ideas in physics. Issue 3. The principle of relativity. 1912, Borgman I.I. , The wave theory of sv * that considers that the manifestation of sv 1\u003e ma is due to vibrations propagating in the form of * waves in the space surrounding the s * t * la t * la; as soon * it turned out ... Category: Mathematics and Science Series: Publisher: YoYo Media,
Coulomb's law determines the strength of the interaction between electric charges, but does not explain how this interaction is transmitted over a distance from one body to another.
Experiments show that this interaction is also observed when electrified bodies are in a vacuum. This means that a medium is not needed for electrical interaction. According to the theory developed by M. Faraday and J. Maxwell, an electric field exists in the space where the electric charge is located.
Electrostatic field - a special type of matter, its source is charges immobile relative to the considered inertial reference system (IFR), through which their interaction is carried out.
Thus, the electrostatic field is material. It is continuous in space. Based on modern concepts, a stationary charged particle is a source of an electrostatic field, and the presence of a field is a sign of the existence of the most charged particle. The interaction of electric charges is reduced to the following: charge field q 1 acts on charge q 2, and the charge field q 2 acts on charge q 1 . These interactions are not transmitted instantly, but at a finite speed, equal speed Sveta from \u003d 300,000 km / s. The electric field created by stationary electric charges relative to the considered IFR is called electrostatic.
We cannot directly perceive the electrostatic field with our senses. We can judge the existence of an electrostatic field by its actions. The electrostatic field of a charge acts with some force on any other charge that appears in the field of a given charge.
The force with which the electrostatic field acts on the electric charge introduced into it is called electric force.
The effect of an electrostatic field on a charge depends on the location of the charge in this field.
If there are several charged bodies located at different points in space, then at any point in this space the joint action of all charges will appear, i.e. the electrostatic field created by all these charged bodies.
Literature
Aksenovich L.A. Physics in high school: Theory. Tasks. Tests: Textbook. allowance for institutions providing general receipt. environments, education / L. A. Aksenovich, N. N. Rakina, K. S. Farino; Ed. K. S. Farino. - Minsk: Adukatsya i vyhavanne, 2004. - S. 214-215.
E, which is its strength characteristic: The strength of the electrostatic field shows how strong the electrostatic field acts on a single positive electric charge placed at a given point in the field. The direction of the tension vector coincides with the direction of the force acting on the positive charge, and opposite to the direction of the force acting on the negative charge.An electrostatic field is stationary (constant) if its strength does not change over time. Stationary electrostatic fields are created by stationary electric charges.
An electrostatic field is uniform if its intensity vector is the same at all points of the field, if the intensity vector at different points is different, the field is nonuniform. Homogeneous electrostatic fields are, for example, the electrostatic fields of a uniformly charged final plane and a flat capacitor far from the edges of its plates.
One of the fundamental properties of the electrostatic field is that the work of the forces of the electrostatic field when the charge moves from one point of the field to another does not depend on the trajectory of motion, but is determined only by the position of the starting and ending points and the magnitude of the charge. Consequently, the work of the forces of the electrostatic field when the charge moves along any closed trajectory is zero. Force fields with this property are called potential or conservative. That is, the electrostatic field is a potential field, the energy characteristic of which is the electrostatic potential associated with the vector of intensity E ratio:
E \u003d -gradj.
For a graphic representation of an electrostatic field, lines of force (lines of tension) are used - imaginary lines, tangents to which coincide with the direction of the intensity vector at each point of the field.
For electrostatic fields, the principle of superposition is observed. Each electric charge creates an electric field in space, regardless of the presence of other electric charges. The strength of the resulting field created by the system of charges is equal to the geometric sum of the strengths of the fields created at a given point by each of the charges separately.
Any charge in the surrounding space creates an electrostatic field. To detect the field at any point, it is necessary to place a point test charge at the observation point - a charge that does not distort the investigated field (does not cause a redistribution of charges that create the field).
The field created by a solitary point charge q, is spherically symmetric. The modulus of tension of a solitary point charge in vacuum using Coulomb's law can be represented as:
E \u003d q / 4pe about r 2.
Where e about - electrical constant, \u003d 8, 85. 10 -12 F / m.
Coulomb's law, established with the help of torsion weights created by him (see Coulomb scales), is one of the basic laws describing the electrostatic field. It establishes the relationship between the force of interaction of charges and the distance between them: the force of interaction of two point stationary charged bodies in a vacuum is directly proportional to the product of the moduli of charges and inversely proportional to the square of the distance between them.
This force is called Coulomb, and the field is called Coulomb. In a Coulomb field, the direction of the vector depends on the sign of the charge Q: if Q\u003e 0, then the vector is directed along the radius from the charge, if Q? times (? is the dielectric constant of the medium) is less than in vacuum.
The experimentally established Coulomb's law and the principle of superposition make it possible to fully describe the electrostatic field of a given system of charges in a vacuum. However, the properties of the electrostatic field can be expressed in another, more general form, without resorting to the concept of the Coulomb field of a point charge. An electric field can be characterized by the value of the flux of the electric field strength vector, which can be calculated in accordance with the Gauss theorem. Gauss's theorem establishes a relationship between the flow of electric field strength through a closed surface and the charge inside this surface. The intensity flux depends on the distribution of the field over the surface of a particular area and is proportional to the electric charge inside this surface.
If an insulated conductor is placed in an electric field, then on free charges q a force will act in the conductor. As a result, a short-term movement of free charges occurs in the conductor. This process will end when the intrinsic electric field of the charges that have arisen on the surface of the conductor completely compensates for the external field, that is, an equilibrium distribution of charges is established, in which the electrostatic field inside the conductor turns to zero: at all points inside the conductor E \u003d 0, that is, there is no field. The lines of force of the electrostatic field outside the conductor in the immediate vicinity of its surface are perpendicular to the surface. If this were not so, then there would be a component of the field strength, a current would flow along the surface of the conductor and along the surface. The charges are located only on the surface of the conductor, while all points on the surface of the conductor have the same potential value. The surface of a conductor is an equipotential surface. If there is a cavity in the conductor, then the electric field in it is also zero; the electrostatic protection of electrical devices is based on this.
If a dielectric is placed in an electrostatic field, then a polarization process occurs in it - the process of orientation of dipoles or the appearance of dipoles oriented along the field under the influence of an electric field. In a homogeneous dielectric, the electrostatic field due to polarization (see. Polarization of dielectrics) decreases to? time.
An electric charge placed at a certain point in space changes the properties of this space. That is, the charge generates an electric field around itself. An electrostatic field is a special kind of matter.
The electrostatic field does not change over time.
The strength characteristic of the electric field is the strength
The electric field strength at a given point is called the vector physical quantity, numerically equal to the force acting on a unit positive charge placed at a given point of the field.
If the test charge is acted upon by forces from several charges, then these forces are independent according to the principle of superposition of forces, and the resultant of these forces is equal to the vector sum of forces. Principle of superposition (superposition) of electric fields: The electric field strength of the system of charges at a given point in space is equal to the vector sum of the strengths of the electric fields created at a given point in space by each charge of the system separately:or
It is convenient to represent an electric field graphically using lines of force.
Lines of force (lines of electric field strength) are called lines, tangents to which at each point of the field coincide with the direction of the strength vector at a given point.
Lines of force start at a positive charge and end at a negative (Power lines of electrostatic fields of point charges.).
The density of the lines of tension characterizes the field strength (the denser the lines are, the stronger the field).
The electrostatic field of a point charge is inhomogeneous (closer to the charge, the field is stronger).Lines of force of electrostatic fields of infinite uniformly charged planes.
The electrostatic field of infinite uniformly charged planes is homogeneous. An electric field, the strength at all points of which is the same, is called uniform.
Lines of force of electrostatic fields of two point charges.
Potential is an energy characteristic of an electric field.
Potential is a scalar physical quantity, equal ratio potential energy, which has an electric charge at a given point of the electric field, to the magnitude of this charge.The potential shows what potential energy a unit positive charge placed at a given point of the electric field will have. φ \u003d W / q
where φ is the potential at a given point of the field, W is the potential energy of the charge at a given point of the field.
The unit of measurement of potential in the SI system is taken [φ] \u003d B(1V \u003d 1J / C)
For a unit of potential, the potential is taken at such a point, for moving to which from infinity of an electric charge of 1 C, it is required to perform work equal to 1 J.
Considering the electric field created by the system of charges, one should use to determine the field potential superposition principle:
The potential of the electric field of the system of charges at a given point in space is equal to the algebraic sum of the potentials of the electric fields created at a given point in space by each charge of the system separately:
An imaginary surface, at all points of which the potential takes the same values, is called equipotential surface.When an electric charge moves from point to point along the equipotential surface, its energy does not change. An infinite set of equipotential surfaces for a given electrostatic field can be constructed.
The intensity vector at each point of the field is always perpendicular to the equipotential surface drawn through this point of the field.
The entire surrounding space is permeated by electromagnetic fields.
There are natural and man-made sources of electromagnetic fields.
Natural sources of electro magnetic field:
- atmospheric electricity;
- radio emission from the Sun and galaxies ( relict radiationuniformly distributed in the Universe);
- electric and magnetic fields of the Earth.
Sources technogenic electromagnetic fields are various transmitting equipment, switches, separating high-frequency filters, antenna systems, industrial installations equipped with high-frequency (HF), ultra-high-frequency (UHF) and microwave (microwave) generators.
Sources of electromagnetic fields in production
There are two large groups of sources of EMF in production:
Dangerous effects on workers can be caused by:
- RF EMF (60 kHz - 300 GHz),
- electric and magnetic fields of industrial frequency (50 Hz);
- electrostatic fields.
Sources of radio frequency waves are primarily radio and television broadcasting stations. The radio frequency classification is given in table. 1. The effect of radio waves largely depends on the characteristics of their propagation. It is influenced by the nature of the relief and cover of the Earth's surface, large objects and structures located on the way, etc. Forests and uneven terrain absorb and scatter radio waves.
Table 1. RF range
Electrostatic fieldsare created in power plants and during electrical processes. Depending on the sources of formation, they can exist in the form of an electrostatic field itself (the field of stationary charges). In industry, electrostatic fields are widely used for electro-gas cleaning, electrostatic separation of ores and materials, electrostatic application of paints and varnishes and polymer materials. Static electricity is generated during the manufacture, testing, transportation and storage of semiconductor devices and integrated circuits, grinding and polishing of cases for radio and television receivers, in the rooms of computer centers, in duplicating equipment, as well as in a number of other processes where dielectric materials are used. Electrostatic charges and the electrostatic fields created by them can arise when dielectric fluids and some bulk materials move through pipelines, pouring dielectric fluids, or rolling film or paper into a roll.
Magnetic fields are created by electromagnets, solenoids, capacitor-type installations, cast and sintered magnets, and other devices.
Sources of electric fields
Any electromagnetic phenomenon, considered as a whole, is characterized by two sides - electrical and magnetic, between which there is a close connection. The electromagnetic field also always has two interconnected sides - the electric field and the magnetic field.
A source of industrial frequency electric fields are the current-carrying parts of operating electrical installations (power lines, inductors, capacitors of thermal installations, feeder lines, generators, transformers, electromagnets, solenoids, half-period or capacitor-type pulse installations, cast and sintered magnets, etc.). Long-term exposure to an electric field on the human body can cause disruption of the functional state of the nervous and cardiovascular systems, which is expressed in increased fatigue, decreased quality of work, pain in the heart, changes in blood pressure and pulse.
For an electric field of industrial frequency in accordance with GOST 12.1.002-84, the maximum permissible level of electric field strength, in which it is not allowed to stay in which without the use of special protective equipment during the entire working day, is 5 kV / m. In the interval over 5 kV / m to 20 kV / m inclusive, the permissible residence time T (h) is determined by the formula T \u003d 50 / E - 2, where E is the intensity of the acting field in the controlled area, kV / m. With a field strength above 20 kV / m up to 25 kV / m, the time spent by personnel in the field should not exceed 10 minutes. The maximum permissible value of the electric field strength is set equal to 25 kV / m.
If it is necessary to determine the maximum permissible electric field strength for a given residence time in it, the intensity level in kV / m is calculated using the formula E - 50 / (T + 2), where T is the time spent in the electric field, h.
The main types of collective protection means against the effects of an electric field of industrial frequency currents are shielding devices - component electrical installation designed to protect personnel in open switchgears and overhead power lines (Fig. 1).
The shielding device is necessary when inspecting equipment and during operational switching, monitoring the production of work. Structurally, shielding devices are made in the form of canopies, awnings or partitions made of metal ropes. rods, nets. Shielding devices must be anti-corrosive and grounded.
Figure: 1. Shielding canopy over the passage to the building
To protect against the influence of an electric field of industrial frequency currents, shielding suits are also used, which are made of a special fabric with metallized threads.
Sources of electrostatic fields
At enterprises, substances and materials with dielectric properties are widely used and obtained, which contributes to the generation of static electricity charges.
Static electricity is generated by friction (contact or separation) of two dielectrics against each other or dielectrics against metals. At the same time, electric charges can accumulate on the rubbing substances, which easily drain into the ground if the body is a conductor of electricity and it is grounded. On dielectrics, electric charges are held for a long time, as a result of which they are called static electricity.
The process of the appearance and accumulation of electric charges in substances is called electrification.
The phenomenon of static electrification is observed in the following main cases:
- in the flow and when splashing liquids;
- in a stream of gas or steam;
- upon contact and subsequent removal of two solid
- dissimilar bodies (contact electrification).
A discharge of static electricity occurs when the intensity of the electrostatic field above the surface of a dielectric or conductor, due to the accumulation of charges on them, reaches a critical (breakdown) value. For air, the breakdown voltage is 30 kV / cm.
People working in the area affected by the electrostatic field have a variety of disorders: irritability, headache, sleep disturbance, loss of appetite, etc.
Permissible levels of intensity of electrostatic fields are established by GOST 12.1.045-84 “Electrostatic fields. Allowable Levels at Workplaces and Requirements for Conducting Control "and the Sanitary and Hygienic Standards for Allowable Electrostatic Field Strength (GN 1757-77).
These regulatory legal acts apply to electrostatic fields created during the operation of high-voltage direct current electrical installations and electrification of dielectric materials, and establish permissible levels of intensity of electrostatic fields at personnel workplaces, as well as general requirements for monitoring and protective equipment.
The permissible levels of the intensity of electrostatic fields are set depending on the time spent at the workplace. The maximum permissible level of intensity of electrostatic fields is 60 kV / m for 1 hour.
When the intensity of electrostatic fields is less than 20 kV / m, the residence time in electrostatic fields is not regulated.
In the voltage range from 20 to 60 kV / m, the permissible time spent by personnel in an electrostatic field without protective equipment depends on the specific voltage level at the workplace.
Measures of protection against static electricity are aimed at preventing the occurrence and accumulation of static electricity charges, creating conditions for the dissipation of charges and eliminating the danger of their harmful effects. Basic protection measures:
- prevention of the accumulation of charges on electrically conductive parts of the equipment, which is achieved by grounding equipment and communications on which charges may appear (devices, tanks, pipelines, conveyors, unloading devices, overpasses, etc.);
- reducing the electrical resistance of the processed substances;
- the use of static electricity neutralizers, which create positive and negative ions near electrified surfaces. Jonah, charge carriers, opposite to the surface charge, are attracted to it and neutralize the charge. According to the principle of operation, neutralizers are divided into the following types: corona discharge (induction and high voltage), radioisotope, the action of which is based on the ionization of air by alpha radiation from plutonium-239 and beta radiation from promethium-147, aerodynamic, representing an expander chamber, in which using ionizing radiation or corona discharge, ions are generated, which are then supplied by an air stream to the place of formation of static charges;
- reducing the intensity of static electricity. It is achieved by appropriate selection of the speed of movement of substances, excluding spraying, crushing and spraying of substances, removal of electrostatic charge, selection of friction surfaces, cleaning combustible gases and liquids from impurities;
- drainage of static electricity charges that accumulate on people. This is achieved by providing workers with conductive footwear and antistatic gowns, the device of electrically conductive floors or earthed areas, platforms and work platforms. grounding of door handles, handrails of stairs, handles of devices, machines and apparatus.
Sources of magnetic field
Power frequency magnetic fields (MF) arise around any electrical installations and power frequency conductors. The higher the current, the higher the intensity of the magnetic field.
Magnetic fields can be constant, pulsed, infra-low-frequency (up to 50 Hz), variable. The action of the MP can be continuous and intermittent.
The degree of influence of the MF depends on its maximum intensity in the working space of a magnetic device or in the zone of influence of an artificial magnet. The dose received by a person depends on the location of the workplace in relation to the MP and the mode of work. Constant MPs do not cause any subjective influences. Under the action of variable MF, characteristic visual sensations, the so-called phosphenes, are observed, which disappear at the moment of cessation of exposure.
With constant work under conditions of exposure to MF that exceed the maximum permissible levels, dysfunctions of the nervous, cardiovascular and respiratory systems, digestive tract, and changes in blood composition develop. With a predominantly localized effect, vegetative and trophic disorders can occur, as a rule, in the area of \u200b\u200bthe body under the direct influence of the MP (most often of the hands). They are manifested by a feeling of itching, pallor or cyanosis of the skin, swelling and thickening of the skin, in some cases, hyperkeratosis (keratinization) develops.
The strength of the MP at the workplace should not exceed 8 kA / m. The intensity of a MP power transmission line with a voltage of up to 750 kV usually does not exceed 20-25 A / m, which does not pose a danger to humans.
Sources of electromagnetic radiation
Sources of electromagnetic radiation in a wide frequency range (super- and infra-low-frequency, radio frequency, infrared, visible, ultraviolet, X-ray - Table 2) are powerful radio stations, antennas, microwave generators, induction and dielectric heating installations, radars, lasers, measuring and monitoring devices, research installations, medical high-frequency devices and devices, personal electronic computers (PC), video display terminals on cathode-ray tubes, used both in industry, scientific research, and in everyday life.
Microwave ovens, televisions, mobile phones, and cordless telephones are also sources of increased electromagnetic radiation hazards.
Table 2. Spectrum of electromagnetic radiation
Low frequency radiation
Production systems are sources of low frequency radiation. transmission and distribution of electricity (power plants, transformer substations, power transmission systems and lines), power grids of residential and office buildings, electrically driven transport and its infrastructure.
Prolonged exposure to low-frequency radiation may cause headaches, changes in blood pressure, fatigue develop, hair loss, brittle nails, weight loss, and a persistent decrease in working capacity may occur.
To protect against low-frequency radiation, either radiation sources (Fig. 2) or areas where a person can be shielded.
Figure: 2. Shielding: a - inductor; b - capacitor
Sources of radio frequency radiation
The source of RF EMF are:
- in the range of 60 kHz - 3 MHz - unshielded elements of equipment for induction processing of metal (injection, annealing, melting, soldering, welding, etc.) and other materials, as well as equipment and devices used in radio communication and broadcasting;
- in the range 3 MHz - 300 MHz - unshielded elements of equipment and devices used in radio communications, broadcasting, television, medicine, as well as equipment for heating dielectrics;
- in the range 300 MHz - 300 GHz - unshielded elements of equipment and instruments used in radar, radio astronomy, radio spectroscopy, physiotherapy, etc. Long-term exposure to radio waves on various systems of the human body causes different consequences.
The most characteristic deviations in the central nervous system and the human cardiovascular system when exposed to radio waves of all ranges are. Subjective complaints - frequent headache, drowsiness or insomnia, fatigue, weakness, excessive sweating, memory loss, distraction, dizziness, darkening of the eyes, an unreasonable feeling of anxiety, fear, etc.
The influence of the electromagnetic field of the medium-wave range with prolonged exposure to is manifested in excitatory processes, violation of positive reflexes. Changes in the blood are noted, up to leukocytosis. Dysfunction of the liver, dystrophic changes in the brain, internal organs and the reproductive system.
The short-wavelength electromagnetic field provokes changes in the adrenal cortex, cardiovascular system, bioelectrical processes of the cerebral cortex.
VHF EMF causes functional changes in the nervous, cardiovascular, endocrine and other systems of the body.
The degree of danger of exposure to a person of microwave radiation depends on the power of the source of electromagnetic radiation, the mode of operation of the emitters, design features of the emitting device, EMF parameters, energy flux density, field strength, exposure time, size of the irradiated surface, individual properties of a person, location of workplaces and efficiency protective measures.
Distinguish between thermal and biological impact Microwave radiation.
The thermal effect is a consequence of the absorption of the energy of the EMF microwave radiation. The higher the field strength and the longer the exposure time, the more pronounced the thermal effect. At an energy flux density of W - 10 W / m 2, the body cannot cope with heat removal, the body temperature rises and irreversible processes begin.
The biological (specific) effect is manifested in the weakening of the biological activity of protein structures, disruption of the cardiovascular system and metabolism. This effect is manifested when the EMF intensity is less than the thermal threshold, which is equal to 10 W / m 2.
Exposure to EMF microwave radiation is especially harmful to tissues with an underdeveloped vascular system or insufficient blood circulation (eyes, brain, kidneys, stomach, gall and bladder). Irradiation of the eyes can lead to clouding of the lens (cataracts) and burns to the cornea.
To ensure the safety of work by sources of electromagnetic waves, a systematic control of the actual standardized parameters is carried out at workplaces and in places where personnel may be located. The control is carried out by measuring the strength of the electric and magnetic fields, as well as by measuring the energy flux density.
Protection of personnel from exposure to radio waves is applied in all types of work if the working conditions do not meet the requirements of the standards. This protection is carried out in the following ways:
- matched loads and power absorbers that reduce the strength and density of the field of the energy flux of electromagnetic waves;
- shielding the workplace and radiation source;
- rational placement of equipment in the workroom;
- selection of rational operating modes of equipment and personnel working regime.
The most effective use of matched loads and power absorbers (antenna equivalents) in the manufacture, adjustment and testing of individual blocks and complexes of equipment.
An effective means of protection against the effects of electromagnetic radiation is the shielding of radiation sources and the workplace with screens that absorb or reflect electromagnetic energy. The choice of screen design depends on the nature of the technological process, source power, and wavelength range.
Reflective screens are made of materials with high electrical conductivity, such as metals (in the form of solid walls) or cotton fabrics with a metal base. Solid metal shields are the most effective and even at a thickness of 0.01 mm provide an attenuation of the electromagnetic field by about 50 dB (100,000 times).
Materials with poor electrical conductivity are used for the manufacture of absorbing screens. Absorbent screens are made in the form of compressed rubber sheets of a special composition with conical solid or hollow spikes, as well as in the form of porous rubber plates filled with carbonyl iron, with an pressed-in metal mesh. These materials are glued to the frame or to the surface of the radiating equipment.
An important preventive measure for protection against electromagnetic radiation is the fulfillment of the requirements for the placement of equipment and for the creation of premises in which sources of electromagnetic radiation are located.
Personnel protection from overexposure can be achieved by placing HF, UHF and UHF generators, as well as radio transmitters in specially designated areas.
The screens of radiation sources and workplaces are blocked with disconnecting devices, which makes it possible to exclude the operation of the radiation equipment when the screen is open.
The permissible levels of exposure to workers and the requirements for monitoring at workplaces for electromagnetic fields of radio frequencies are set out in GOST 12.1.006-84.