ELECTROMAGNETIC FIELD

From Big Medical Encyclopedia

ELECTROMAGNETIC FIELD — the special form of matter, by means of a cut is carried out interaction between electrically charged particles. Electromagnetic energy is widely used in a radio communication, television, a radar-location; for implementation of various technological processes and operations (heating, welding, a dusting of metals, drying of various materials, dielectric processing of plastic), for such types of heat treatment of foodstuff as defrosting, sterilization, sublimation, and also in scientific research. In medicine energy of the electromagnetic field is applied in physical therapy (see the Diathermy, Microwave therapy) to bystry removal of a hypothermia after open heart operations, to heating of blood at transfusions.

The main sources of radiations during the use of electromagnetic energy are various types of antenna arrangements, working elements of high-frequency installations, melting, hardening inductors, working condensers for implementation of dielectric heating, various elements of lamp and machine generators. In vacuum E. the item is characterized by a vector of electric field strength (E) and magnetic induction (V), to-rye determine forces operating from zero on motionless and (or) moving charged particles: in the environment, napr, in air, fabrics — in addition two auxiliary sizes: magnetic field strength (N) and electric induction (D). AA. the item of motionless and evenly moving charged particles it is inseparably linked with these particles. At their accelerated movement E. the item is radiated in the form of quanta (photons) and exists in the form of electromagnetic waves, to-rye represent the interconnected changes of tension electric and magnetic water. Key parameters of an electromagnetic wave are: wavelength (λ) — distance, on a cut extends a wave for one period (T); frequency of fluctuations (f) — number of fluctuations in one second; rate of propagation of an electromagnetic wave (V) equal λ/Т.

Depending on energy of photons (V-quanta) all range of electromagnetic radiation (see) can be subdivided into area of not ionizing and ionizing radiation. Electromagnetic oscillations, energy of quanta carry to not ionizing radiation to-rykh it is insufficient for ionization of molecules and atoms of substance; to ionizing radiation — electromagnetic oscillations, quanta to-rykh at interaction with substance cause ionization of atoms. A part of a range of not ionizing radiation is made by radiations of radio wave range, other part belongs to radiations of optical range, to-ry it is accepted to subdivide into infrared radiation (see), visible light (see) and ultraviolet radiation (see). The most long-wave part of radiations of radio wave range is closed with quasistatic electric (see. Electrostatic field) and magnetic fields (See. Magnetic field), the least short-wave part (ultraviolet And) adjoins X-ray (see. X-ray emission).

On a source of emergence electromagnetic radiations are subdivided into radiations artificial (anthropogenous) and natural (terrestrial, solar, galactic) origins. Also electromagnetic oscillations, emergence shall be referred to the last to-rykh it is connected with course of processes of life activity at various levels of the organization of live systems. Feature of artificial electromagnetic radiations is their high temporary and space coherence causing a possibility of considerable concentration of energy in narrow spectral ranges whereas for natural the wide range of frequencies is characteristic.

The field of distribution of electromagnetic waves can be subdivided into three zones: near (zone of induction), intermediate and distant (wave). Power indicator E. the item of near and intermediate zones is volumetric energy density. At assessment E. items of these zones from hygienic positions consider tension electric (in oil) and magnetic (car) of components. In a wave zone E. items estimate on the flux density of energy (FDE), edges is expressed in vt*m - 2 , mvt*sm - 2 , mkvt*sm - 2 .

At influence E. items on an organism the operating factor are the induced internal fields. Their parameters and distribution in a body of the person depend on the frequency of electromagnetic oscillations, electric properties of fabrics, a form and the sizes of a body and its orientation concerning vectors of tension electric (E) and magnetic (N) of fields. Electric properties of fabrics substantially are defined by frequency influencing E. item. With one frequencies fabric shows properties of the conductor, at others — the insulator (dielectric). One of the main indicators characterizing electric properties of fabrics are their dielectric constant and magnetic permeability. On dielectric properties all biol. fabrics can be subdivided into two groups: to fabrics with the high content (over 80%) of water blood, muscles, skin, tissue of a brain, liver, kidneys, spleens, etc., belong to fabrics with rather low water content — fatty and bone (see Conductivity of biological systems). On magnetic properties of tissue of body treat weak diamagnetics and paramagnetics. Their magnetic permeability practically does not differ from magnetic permeability of air owing to what the magnetic field strength in fabrics practically does not differ from tension of external magnetic field. Variation magnetic field directs vortex electric field of induction in fabrics, a cut, in turn, causes fluctuations of ions and dipole molecules of the environment that eventually leads to absorption of energy and formation of heat.

The action spectrum of electromagnetic radiations of radio-frequency range is limited preferential to heating of substance. Absorption of energy E. the item in fabrics is defined by two processes: fluctuation of free charges and fluctuation of dipole molecules with a frequency of the influencing field. The first process leads to power losss at the expense of electric environmental resistance, the second — due to friction of dipole molecules in the viscous environment. Both processes lead to formation of heat and heating of fabrics.

Proceeding from features of interaction E. the item with biological tissues and a body of the person in general all range of electromagnetic radiations of radio frequencies can be subdivided into 5 sites. The first — from units of Hz to 10 kHz, the second — 10 kHz — 30 MHz, the third — 30 MHz — 10 GHz, the fourth — 10 — 200 GHz, the fifth — 200 — 3000 GHz. Since for the electromagnetic oscillations relating to the first frequency range, the wave zone is at distances where intensity E. the item loses the biological importance, in relation to this frequency range practical value is represented by only separate components of the near field (E and N). In relation to an electric component weeding a body of the person has properties of rather good conductor in this connection in a body it is practically absent. At action of magnetic field in tissues of a body are induced magnitno induced electric weed, tension to-rykh is proportional to a magnetic field strength, its frequency and radial distance from an axis of a body.

Also absorption of energy E is characteristic of the second frequency range. item preferential superficial structures of a body. At the same time with increase in frequency the size of an absorbed energy and consequently, and the absorbed power increase approximately in proportion to a square of frequency.

Idiosyncrasy of the third frequency range is emergence of the expressed interferential phenomena resulting in essential distinctions both in the size of the general absorption of energy and in its distribution in a body. The maximum absorption of energy takes place in case of resonant absorption at a certain ratio of wavelength with sizes biol. object. At the same time the absorbed energy is distributed in a body very unevenly, forming areas of so-called hot spots.

Bystry attenuation of energy at its passing through fabrics is characteristic of the fourth frequency range. At general irradiation energy gets into fabrics approximately on depth 0,1 — 0,01 wavelengths. Specific absorption of energy in this case does not depend on the sizes and a shape of a body.

The electromagnetic oscillations relating to the fifth frequency range are absorbed by the most surface layers of skin. The caused cues connect effects only with irritation of receptors of skin or action on biologically active sites.

Under the influence of radio frequencies there are reactions of an organism characterizing the manifestation of radio wave sensitivity, reactions reflecting the phenomena of adaptation character and also the reactions indicating development of radio wave defeats. It is difficult to establish a clear boundary between them, especially at use of electromagnetic radiations in to lay down. purposes. The Nek-ry effects connected with impact on an organism of radiation of high intensity can constitute danger to an organism.

Due to the essential distinction in the nature of absorption of energy E. the item at different frequencies and consequently, and in values of the specific absorbed power development of heat effects is possible at significantly different values of external fields. In the field of resonant frequencies the threshold of emergence of clear thermal effects lies for the person in the range of intensivnost of 5 — 11 met/cm 2 , for the animal average sizes — 2,5 — 5 MW/cm 2 , for small animals — 0,5 — 1 MW/cm 2 . Connect physiological and biochemical reactions with heat effects, and also morfol., changes, the greatest expressiveness to-rykh is shown in structures or bodies with low level of metabolic processes, weak vascularization (a crystalline lens, a vitreous of an eye, a gall bladder) and high sensitivity to temperature increase (seed plants, nek-ry structures of a brain). Characteristic manifestation of thermal action of microwave radiations are disturbance of processes of a spermatogenesis, development of experimental stomach ulcer in animals, formation of a cataract.

It is fullestly studied biol. action of microwave radiations. In relation to the specified frequency range c are the most sensitive. century of page, cardiovascular in immune systems. All biological effects arising at action of microwave radiations can be subdivided into two basic groups: thermal, development to-rykh is caused by essential heating of fabrics, and the non-thermal, arising at rather low intensity influences and which are not followed by integral fervescence.

The reactions of an organism arising at action of non-thermal intensivnost (specific action of microwaves) connect with polarization of membranes, change of their permeability, in t. I. the selection character, with emergence of chemical or structural changes in the synoptic device, in enzymes.

The increasing distribution is got by the concept, according to a cut at the heart of the reactions of an organism arising at action of microwave radiations power processes and processes of information transfer lie. Refer changes and reactions, emergence to power processes to-rykh entirely is defined by quantity of an absorbed energy or power of electromagnetic radiation. Processes of information transfer make a basis of reactions, at to-rykh effect of influence of electromagnetic radiation is carried out via one of channels of transfer and information processing (e.g., points of acupuncture, nervous, neuroendocrinal, humoral and nek-ry other systems).

The question of safe levels of electromagnetic radiations continues to remain a subject of discussions and is solved in the different countries differently. Acting in world practice a gigabyte. standards in the form of standards, health regulations, the recommendations establishing the marginal level (ML) of electromagnetic radiations of radio frequencies provide various solution of a question of the contingents of persons, in relation to the Crimea the regulation is carried out. Standards of the majority of the Western European countries establish PDU only for the personnel servicing sources of electromagnetic radiations. In the nek-ry countries operation of the same regulations extends both to personnel, and to the population (e.g., in the USA). Standards of a number of the socialist countries (ChSSR, the Party of Russian Taxpayers), and also Sweden identify PDU of radio wave influences for two contingents persons: professionally connected with influence of this factor and the population.

In the USSR and a number of the socialist countries depending on the place and conditions of influence it is accepted to distinguish four types of radiation: professional, nonprofessional, radiation in life and carried out In to lay down. purposes.

For the frequency range of 300 MHz — 300 GHz as the normalized parameters of radiation are established: for the population in general — a radiation intensity of silt the flux density of energy (PPE, mkvt*sm - 2 ); for various categories working along with intensity power loading (Ew) is normalized. The last represents the work PPE of the falling radiation for the period of (T) its influence: Ew = * T is also expressed to PPE in vt*chas/m - 2 (mkvt*chas/m - 2 ). Hygienic standards established limiting values as PPE, and Ew. In the range of their admissible values the size PDU of radiation is determined by a formula: Pduppe = Ew/T; T = Ew/Pduppe

In frequency range to 300 MHz as the normalized parameters tensions E and H fields are used.

Clinical manifestations of radio wave influences are fullestly investigated concerning action of microwave fields. In absolute majority of the countries «a radio wave disease» as occupational disease does not appear. Nek-ry researchers find it possible to allocate a radio wave syndrome. It is accepted to distinguish two forms of frustration: acute and chronic. Hron. the form is subdivided into three degrees: easy, moderately severe and heavy. Accurate criteria of this division are absent.

Acute forms of defeats meet extremely seldom. Their emergence is connected with emergencies or gross violation of safety regulationss. Of them the expressed polisindromnost is characteristic. Are most often observed ostrorazvivayushcheesya an asthenoneurotic condition and disturbance of functions of cardiovascular system. At rather low levels of influence there are dizziness, weakness, a headache, nausea, to-rye are quite often combined with change of a rhythm of cordial reductions (tachycardia, is more rare bradycardia), changes of the ABP. At the same time originally developing hypertensive reaction quickly is replaced by hypotonia. Local vasomotor spasms are observed. The arisen disturbances differ in firmness and remain up to 1,5 — 2 months. At very intensive influences (about hundreds of MW/cm 2 or several W/cm 2 ) along with the listed symptoms development of a cataract and defeat of seed plants are possible. Specific wedge. symptoms of radio wave pathology are not established.

For a clinical picture hron. influences of the increased levels of radio wave radiations development of asthenic states in vegetative frustration, hl is characteristic. obr. from cardiovascular system (a radio wave syndrome). Along with the general astenisation which is characterized by weakness, increased fatigue, an uneasy dream patients often have headaches, easing of memory, dizziness, psychoemotional lability, pains in heart, the increased perspiration, a loss of appetite; frustration of a menstrual cycle, decrease in a sexual potentiality are less often noted. Objective symptoms of a disease are the Crocq's disease, a regional hyperhidrosis, a cold snap of brushes and feet, a tremor a century and fingers of hands, lability of pulse and arterial pressure with bent to bradycardia and hypotonia, a perversion of reactions of vessels to the Cold irritant, muting of cardiac sounds, diencephalic crises, change of function of a thyroid gland (hyperfunction), gonads and gipotalamo - pituitary and adrenal system. A characteristic sign consider instability of quantity of leukocytes in blood, edges it can be shown both by a leukopenia, and a leukocytosis.

The diagnosis of acute defeat by the microwave field is made on the basis of data of the occupational history (specialty, possible levels and a radiation time in case of an emergency or violation of the rules of the accident prevention), complaints of the patient and results of comprehensive inspection. During the carrying out differential diagnosis it is necessary to exclude the reasons, to-rye can cause development of similar disturbances (overheating, acute intoxications, others of professional harm). Crucial importance at establishment of the diagnosis hron. defeats have the occupational history and data of periodic medical surveys.

Treatment. Pathogenetic the reasonable scheme of treatment does not exist. In case of acute defeats the first stage includes the actions of acute management directed to elimination and the prevention of disturbances of cardiovascular system. At easy defeats sedative, symptomatic and fortifying means are shown. In case of the expressed pathology treatment in a hospital with the subsequent temporary transfer for the work which is not connected with influence E is shown. item of radio frequencies. At absence to lay down. effect, and also at the expressed forms of diseases after treatment transfer into work out of contact with professional vrednost is shown.

The prevention of adverse action of electromagnetic radiations of radio frequencies is reached by system of hygienic, treatment-and-prophylactic and technical actions. Gigabyte. actions provide establishment of PDU for the corresponding categories of the faces which are professionally tied and not tied with influence of electromagnetic radiations and also for the population, implementation of metrological control of observance of PDU, check of efficiency of these actions, justification of a work-rest schedule of the faces which are professionally tied with influence of this factor. In relation to this category of persons have essential value to lay down. - the prof. of an action providing carrying out preliminary and periodic medical surveys (see. Medical examination). Technical actions provide implementation of a complex of the protective measures directed to decrease in levels of electromagnetic radiations in workplaces of personnel and in selitebny territories to the values which are not exceeding PDU. Decrease in levels of electromagnetic radiations is reached due to removal of the radiations working from sources; uses of the equivalent loadings absorbing energy; implementation of metrological control In a zone of jobs in the terms established by normative documents. Depending on the frequency of electromagnetic oscillations and the nature of radiation the shielding or radio absorbing materials of various type are applied. For protection against microwave fields, UVCh-fields and VCh-fields, and also the electric component of electromagnetic oscillations of low and ultralow frequencies uses metal screens; for protection against magnetic fields — materials with low-magnetic permeability (sheet steel, ferromagnetics). In case of impossibility of decrease in levels of electromagnetic radiations to the values established to PDU individual means of protection (radio safety spectacles, guards, radio protective overalls) are applied. Control of observance of PDU at the enterprises is exercised departmental sanitary about myshlenny laboratories, in medical and research establishments — the SES specialized laboratories. The last control also selitebny territories (see. Sanitary inspection).

Bibliography: Biological effect of electromagnetic radiations, under the editorship of B. M. Savin and G. A. Stepansky, M., 1978; Introduction to electromagnetic biology, under the editorship of G. F. Plekhanov, Tomsk, 1979; Occupational health at influence of electromagnetic fields, under the editorship of V. E. Kovshilo. M, 1983, bibliogr.; Guskova A. K. and Kochanova B. M. Some aspects of etiological diagnosis of occupational disease in connection with influence of microwave radiation, the Gigabyte. work and the prof. having got sick., No. 3, page 14, 1976; Davydov B. I., Tikhonchuk V. S. and Antipov V. V. Biological effect, rationing and protection against electromagnetic radiations, M., 1984; Dumansky Yu. D., Serdyuk A. M. and I. P's Elk. Influence of electromagnetic fields of radio frequencies on the person, Kiev, 1975, bibliogr.; Methodological questions of hygienic rationing of electromagnetic radiations of radio-frequency range, under the editorship of B. M. Savin, M., 1980; Tolgskaya M. S. and Gordon 3. B. Morphological changes at action of electromagnetic waves of radio frequencies, M., 1971; Biological effects and dosimetry of nonionizing radiation: Radiofrequency and Micro ware energies, ed. by M. Grandolfo a. o., N. Y. — L., 1983; Nonionizing radiation protection, ed. by M. J. Suess, Copenhagen, 1982.

B. M. Savin.

Яндекс.Метрика