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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
Dangers of electricity: real, imaginary and unexplored. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Electricity for beginners Talk about the harmful effects of electromagnetic fields (EMF) began in the late 20s, when a technique appeared that operated at relatively high currents in the high frequency (HF) range. And after the war, they began to seriously study the biological effects of radars, HF, UHF and microwave devices. All attention was directed to the thermal effects of ultra-hyphen and microwave frequencies. The thermal model of impact was based on the possibility of unacceptable overheating of the human body or individual organs in the EMF zone (the effect of "a man in a microwave oven"). If we talk about relatively low frequencies (from 50 Hz to hundreds of kHz), then the generally accepted point of view was as follows: the density of the current induced in biological tissues by alternating magnetic and electric fields should be significantly lower than the density of biocurrents flowing in living tissues. Overheating (as in microwave) was excluded. All other effects that were observed from time to time were attributed to artifacts - processes that sometimes occur during the study of the body as a result of exposure or processing and are not normally characteristic of it. For the possible biological effect of constant EMF, they made an indulgence and assumed that a constant electric field has some effect on living cells, but they completely denied this to a constant magnetic field. This was argued by the fact that the energy of interaction of the magnetic field with biological molecules is several orders of magnitude less than the energy of the thermal motion of molecules. Today, this opinion causes a smile. In fairness, it must be said that the idea of the effect of weak fields on the body was to a certain extent discredited by some data of magnetobiological experiments published in the literature, the formulation of which did not stand up to criticism. In the 1970s, specialists returned to the effects of weak and very weak magnetic and electric fields on model physicochemical systems, biological objects, and the human body. The mechanisms that cause these effects "work" at the level of molecules, and sometimes atoms, as a result of which they are very difficult to detect. Nevertheless, scientists have experimentally demonstrated and theoretically explained magnetic and spin effects. It turned out that although the energy of magnetic interaction is several orders of magnitude less than the energy of thermal motion, but at that stage of the reaction, where everything actually happens, thermal motion does not have time to interfere with the action of the magnetic field. This discovery makes us take a fresh look at the very phenomenon of life on Earth, which arose and developed in the conditions of the geomagnetic field. The laboratory showed the effect of relatively weak (an order of magnitude or two higher than geomagnetic) permanent and variable magnetic fields on the output of the primary reaction of photosynthesis - the foundation of the entire ecosystem of our planet. This influence turned out to be small (less than a percent), but something else is important: proof of its real existence. The second important discovery is the presence of the so-called "windows of sensitivity" of living and model physical and chemical objects to the frequency and magnitude of the fields. In 1985, it was first established that the frequencies of the "sensitivity windows" of biological objects coincide with the cyclotron frequencies in a given constant magnetic field of ions of key molecules in various biochemical reactions. The phenomenon is named biological cyclotron resonance. Experiments have shown that the effect produced at the cyclotron frequency by an alternating magnetic field is determined by the value of its projection on the direction of the constant magnetic field. If the directions of the fields are perpendicular, then there are no effects. At a low constant magnetic field, biological cyclotron resonance can manifest itself at low frequencies. Thus, in the geomagnetic field of Novosibirsk and Yakutsk, the cyclotron resonance frequency is close to 50 Hz, i.e., to the frequency of the alternating current in the network. And for the geomagnetic field of Moscow, it is lower. In reinforced concrete houses, the cyclotron resonance frequency is distorted. What does all this mean in practice, in everyday life? We iron with an electric iron at those moments when the position of the iron and the Earth's magnetic field create a position in which calcium ions in our cells come into a state of magnetic resonance. Simply put, they begin to behave in cells not as they should. Whether this is good or bad, we will consider a little later, but now let's pay attention to something else. TV, electric stove, washing machine, computer and other household electrical appliances that surround us, at a certain position relative to our body (or our body relative to appliances) can affect the electrochemical processes occurring in the cells of the body. This circumstance explains the complexity of studying the influence of weak fields on living organisms. It is enough to rearrange the table with the experimental setup, change its orientation in space, as the experiments ceased to be obtained. In other laboratories where they tried to replicate experiments published in reputable journals, nothing could immediately work out! It is not long before colleagues are accused of quackery or scientific forgery. But the reader is not interested in the problems of scientists, but in the question: is it good or bad to live with an increased background of electromagnetic fields? Evolutionarily, all life on Earth is not adapted to the rapid increase or sharp fluctuations in the EMF surrounding us. Let's take radiation as an example. Man has adapted to survive huge temperature fluctuations, incredible levels of chemical pollution of the environment, but he has no protection against an increase in the radioactive background. We do not have evolutionary established mechanisms for counteracting ionizing radiation. We also do not have mechanisms for neutralizing electric and magnetic fields that have other characteristics than natural ones. Until recently, as a biological species, man existed in conditions of a small magnetic field and in even smaller low-frequency electromagnetic fields, the main sources of which are near and far electromagnetic pulses caused by thunderstorms, and disturbances that arise in the Earth's magnetosphere when solar plasma invades it. "Modern humanity, like all living things, lives in a kind of electromagnetic ocean, the behavior of which is now determined not only by natural causes, but also by artificial intervention. We need experienced pilots who thoroughly know the hidden currents of this ocean, its shallows and islands. And we need even more strict navigational rules that help to protect travelers from electromagnetic storms,” one of the pioneers of Russian magnetobiology, Yu.A. Kholodov. Nevertheless, some rules for living surrounded by televisions, irons, washing machines, personal computers, pagers and mobile phones already exist. Let's talk about them. In accordance with the international classification, sources of electromagnetic fields (EMF) are divided into two groups: from 0 to 3 kHz and from 3 kHz to 300 GHz. The first group includes EMF in the frequency range from zero to several hundred thousand Hz - fields of overhead and cable power lines, long-wave radio broadcasting centers, electrified vehicles and household appliances. The second group consists of EMFs of high, ultra-high and ultra-high frequencies (0,3-30 trillion G) - cellular communication systems, microwave ovens and television transmitters. The boundaries of the sanitary protection zones of power lines designed in the Russian Federation to the nearest housing are at least 750 m for power lines 250, and 1150 m for power lines 300. In some countries with a high population density, residential buildings are located even under power lines. It is believed that the main effect is due to the electric field of the AC power line, which induces a displacement current (capacitive) in the human body. We allow permanent stay of people in the field of tension less than 0,5 kV/m. With a field strength 2-4 times higher and a frequency of 50 Hz, the bias current does not exceed one and a half to three tens of microamperes, and a person will not experience any unpleasant sensations. But it is worth touching the car, which is standing next to the power line, and you will be slightly "pulled". The metal roof of the house shields from an alternating electric field only if it is grounded. The non-metallic roof is covered with a metal mesh and grounded. On the wires of high-voltage overhead power lines, the voltage is close to the threshold of a corona discharge in air. In inclement weather, the emerging corona discharge from the AC power line throws into the atmosphere clouds of ions of different signs, the charges of which do not compensate each other. Even far from power lines, the electric field created by the ion cloud on the earth's surface can exceed the natural electric field of the Earth and the maximum permissible levels (MPL). American researcher Louise Jung proposed an original way to demonstrate a corona discharge on power lines. If you approach a power line with a daylight fluorescent lamp at night, then in the presence of a corona discharge, the lamp will begin to glow with a supernatural light, and when the wind gusts, the light inside the lamp will oscillate like a candle flame. Another source of electromagnetic pollution is longwave radio transmitting centers. Once they were placed in residential areas. In the 20-30s of the last century, in Moscow houses located around the radio station named after the Comintern, which broadcast at a wavelength of 2 km, it was possible to conduct such an experiment. If you wind about a hundred turns of wire around the frame and attach a light bulb from a flashlight to the ends, then it lights up. A simple calculation shows that for this the magnetic field strength should not be less than a few A/m. Now in many countries this is the maximum permissible level for an 8-hour working day. Longer radio waves "cover" more space. It is known that the walls of buildings shield the electrical component of the wave, but they weaken the magnetic component a little. In the state of Maine, at one time, a radio communication system was deployed with submarines in the ocean. Sea water strongly absorbs radio waves, but the longer the wavelength, the lower the absorption. For this reason, communication was carried out at a frequency of 15 Hz, i.e., at a wavelength of 20 thousand km. Since the power radiated by an antenna is proportional to the cube of the ratio of its size to the wavelength, the antennas had to be stretched across almost the entire state. But local residents were very lucky: in the geomagnetic field of the state, the frequencies of biological cyclotron resonance (it was not yet discovered then) of ions significant for the body differ markedly from 15 Hz. But the residents of houses near the October Russian Orthodox Church in Moscow were much less fortunate. According to the Institute of Occupational Medicine of the Russian Academy of Medical Sciences, some of the houses ended up in the development restriction zone, where the maximum permissible limits were exceeded. Little reassurance can be said to the residents of many other houses in Moscow, especially those located near the Ostankino television center. The problem is the departmental and private ROCs, which have been growing like mushrooms in recent years. Against the background of the ROC, the antennas of base stations of cellular telephone communications make an insignificant contribution to the electromagnetic pollution of city streets. Another topic of conversation - electric transport, which serves as a source of electric and magnetic fields in the frequency range from 0 to 1 kHz. Railway transport uses alternating current, urban (trolleybuses, trams, metro) - direct. The average values of the magnetic field in suburban electric trains are about 20 μT, in vehicles with a direct current drive - about 30 μT. In trams, where the rails are the return wire, the magnetic fields compensate each other at a much greater distance than in the wires of a trolleybus, inside which the magnetic field fluctuations are small even during acceleration. In this respect, the trolleybus is more environmentally friendly than the tram. Among electric-powered vehicles, the largest fluctuations in the magnetic field are observed in the subway. At the station "Universitet" during the departure of the train, the magnitude of the magnetic field on the platform is 50-100 μT and more, exceeding the geomagnetic field, especially its horizontal component, and even changing direction. And even when the train disappeared into the tunnel for a long time, the magnetic field did not want to return to its previous value. Only after the train passed the next point of connection to the contact rail or was coasting, the magnetic field on the platform returned to the old value. In the metro car itself, the magnetic field is even higher - 150-200 μT, i.e. 10 times higher than in a conventional ground train. Electromagnetic fields in our homes can be roughly divided into two categories: fields of electrical equipment of the building and fields of household appliances inside apartments. The electric field from external electrical equipment in residential buildings, which is created by power transformers on the stairs, cable lines in the entrance, etc., usually small - 1-10 V / m, i.e. below the remote control - 500 V / m. But the magnetic field from it often exceeds the magnetic MPD (0,2 μT). In each case, it all depends on the layout of the house and apartment. A tangible contribution to the alternating electric field in the room is made by internal wiring, which acts as an antenna, radiating at a frequency of 50 Hz. So, household switches are single-pole and break the circuit of only one wire. Therefore, by turning off the table lamp, we thereby reduce the magnetic field from the corresponding section of the wiring to zero. But it is already small, since the currents in a two-wire wire flow in opposite directions and their magnetic fields are subtracted from each other. However, the total electric field of a two-wire wire after the switch is clicked may increase if the neutral wire circuit is broken, and the second wire remains energized. This situation is common, because when wall switches are mounted or electrical appliances with their own switches are connected to socket outlets, few people think which of the wires is zero. A magnetic field from standard household electric stoves at a distance of 20-30 cm from the front panel, where the hostess usually stands, is 1-3 μT (the indicator depends on the modification and condition of the stove). Burners have a larger magnetic field, of course. But at a distance of 50°cm, it is already indistinguishable from the general field in the kitchen, which is approximately 0,1-0,15 µT. Magnetic fields from refrigerators and freezers are small. According to the Center for Electromagnetic Safety, in a conventional household refrigerator, a field higher than the MPD (0,2 μT) occurs within a radius of 10 cm from the compressor and only during its operation, but for refrigerators equipped with a "frost" system, an excess of the MPC can be recorded even for 1 m away from the refrigerator door. Small are the fields from powerful electric kettles. So, at a distance of 20 cm from the teapot "Tefal" the field is about 0,6 μT, and at a distance of 50 cm it is indistinguishable from the general EMF background in the kitchen. For irons, a field above 0,2 μT is detected at a distance of 25 cm from the handle and only in heating mode. The fields of washing machines can be called quite large. Even for small machines, the field at a frequency of 50 Hz at the control panel is more than 10 μT, at a height of 1 m - 1 μT, from the side, at a distance of 50 cm, - 0,7 μT. True, a large wash is not so frequent, in addition, when an automatic or semi-automatic washing machine is running, the hostess can move away or even leave the room where the laundry is being done. An even larger field is created during operation by a vacuum cleaner - about 100 μT. The record holder among household appliances in the respect we are interested in is a small electric razor, the field of which is measured in hundreds of microtesla. The most famous EMFs in an apartment are the fields of personal computers. By their design and by the fields they create, computers are close to television and radio receivers, video and audio recorders, music centers and other equipment that you will find today in almost every home. A computer monitor is a source of both constant and alternating electric fields. The first is undesirable because of the direct biological action, the second - as a factor affecting the balance of air ions in the room. The intensity of a static electric field directly near the screen of cathode-ray tubes of monitors in relatively dry air can reach several hundred kV/m. At a distance of 40-50 cm, it is less: from tens to units of kV/m, but even in this case it is still higher than the MPC. In addition to the electrical component of a computer EMF, there is also a magnetic one. In televisions and monitors, magnetic fields are mainly due to the operation of vertical and line scanning systems, they do not have a pronounced directionality and are approximately the same in front of the screens: at angles of 45, 90 and 180 ° to them. Laptop computers have replaced the cathode ray tube with a liquid crystal screen, but the alternating magnetic field from other elements is still present, and they keep the laptop much closer to themselves during operation than a desktop computer. As a result, for most laptops of different models, recommendations on the levels of magnetic fields are not met. It is impossible to ignore the most odious sources of electromagnetic pollution at high, ultra-high and microwave frequencies - Microwave ovens and radiotelephones (mobile phones) operating in the range of 0,3-3 GHz. By virtue of the principle of their operation, microwave ovens serve as a powerful source of radiation. For this reason, their design requires the presence of appropriate shielding, and the operating time is relatively short - food is heated or cooked quickly. And yet, you should not be near the included microwave. At a distance of 30 cm, it creates a noticeable alternating (50 Hz) magnetic field (0,3-8 μT), so it is better to move a meter or two, where, as measurements show, the energy flux density is below sanitary and hygienic standards. The frequency of mobile phones is lower than that of microwave ovens, and depends on the type of system. Many countries are studying the effects of cellular radiotelephone radiation on both animals and volunteers. They take encephalograms, fix the amount of total brain blood flow, changes in cardiovascular and respiratory activity, the hormonal system, study the effect on cognitive (cognitive) functions, sleep, etc. Most studies of the bioelectrical activity of the brain still note only such changes that can be attributed to a non-specific protective reaction of the body in response to an unpleasant, but weak in its biological significance, impact. The absence of significant changes indicates the subthreshold nature of the changes. However, the fact that the changes were especially clearly recorded after the cessation of irradiation means that some influence still exists and there is an aftereffect. In the course of research, a curious phenomenon was discovered. It turned out that electromagnetic fields of high frequencies, modulated in amplitude, can produce a significantly greater biological effect on a person than unmodulated ones. This means the following: if you just keep the mobile phone turned on near your ear, its effect is one, and if at the other end someone starts talking or just making some sounds (modulating the EMF in amplitude), then the action will be different, and noticeably greater. It follows from this that it is healthier to speak than to listen. In general, we can say that there are still more questions than answers, and everyone can decide for himself what is more profitable and useful for him - to enjoy all the benefits of Civilization or to remain in the Stone Age. True, a person is unlikely to succeed in the latter, at least in inhabited places. Author: Bannikov E.A.
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