With the progress of science and technology, the application of electromagnetic technology has created a huge material civilization to mankind, but also bring people into an environment full of man-made electromagnetic radiation. As early as 1975, experts and scholars have predicted that, with the urban economic development and population growth, electronics, communications, computers, automobiles and electrical equipment into a large number of families, the urban space man-made electromagnetic energy increased by 7%-14% per year, that is to say, 25 years after the maximum increase in environmental electromagnetic energy density can be increased by 26 times, 50 years after the maximum increase of 700 times, the 21st century! The urban electromagnetic environment will be more complex and deterioration.
Electromagnetic radiation refers to "the phenomenon of energy in the form of electromagnetic waves emitted from a source into space". Electromagnetic environment is "the sum of all electromagnetic phenomena existing in a given place". The deterioration of the electromagnetic environment not only causes serious harm to communications, computers and various electronic systems on which human life is increasingly dependent, but also poses a threat to human health. For this reason, countries around the world have attached great importance to the increasingly complex electromagnetic environment and its wide range of impact, electromagnetic environmental protection and electromagnetic compatibility technology has become a rapidly developing new subject areas.
Over the past two decades, China's economy and urbanization have developed rapidly, and the electromagnetic environment in urban airspace has become more complex, with many new phenomena and problems. Mainly: (1) due to the development and expansion of the city, some large and medium-sized radio and television broadcasting and radio communication transmitter stations are newly developed residential areas surrounded by local residents living areas to form a strong field; (2) mobile communications technology (including cell phone communications, paging communications, trunking professional network communications) rapid development of high-rise buildings in urban areas set up hundreds of mobile communications transmitter base stations, these sources of electromagnetic radiation, although the power of each is not large (100W or less), the power of each is not very high. Each power is not large (100W or less), but due to the blossoming of the urban area, so that the city's high altitude electromagnetic wave field strength enhancement, local high-rise buildings are contaminated. In addition, there are many microwave directional antennas, satellite dishes and short-wave antennas on the high-rise buildings in the city; (3) with the increase in electricity consumption in the city and the implementation of urban power grid renovation project, 110KV and 220KV high-voltage substations into the city center, either indoors or outdoors, or on the ground or underground, causing panic and complaints from the neighboring people; (4) the rapid development of urban transportation systems (automobiles, trolley buses, subways, light railways and electrified railways) caused by the city. Electrified railroad) the rapid development of urban electromagnetic noise caused by the rising trend; (5) personal means of radio communication and household appliances increased, the electromagnetic energy density of the family environment increased, the indoor electromagnetic environment and the outdoor electromagnetic environment has been integrated, the total amount of electromagnetic environment in the city is increasing.
Characterization of radiation analysis of typical electromagnetic radiation equipment in the city
Characterization of radiation analysis of the ten hotspots in China's urban electromagnetic environment is as follows:
A radio and television broadcasting towers located in the urban area
Most of the broadcasting and television towers are built in the center of the city of the densely populated, so that there is a higher field strength in the service area. China's television and FM broadcasting frequency range is: 48.5MHz-960MHz, belonging to the ultra-short wave and decimeter wave band, electromagnetic waves for the space linear propagation. In our country TV, FM equipment are installed in the same transmitter, TV and FM antennas are installed in the vast majority of the same tower on the mast.
Beijing Central Radio and Television Tower, Shanghai Oriental Pearl Tower and Tianjin Sky Tower electromagnetic radiation acceptance shows that: tower height of more than 400 meters, the total transmitter power of more than 200KW of the city's tall TV tower around the ground and high-level electromagnetic radiation environment power density of a few μW/cm2, are smaller than the national standard of the band of 40 μW/cm2 standard. Measurement results show that built in the urban areas of the high radio and television tower despite the transmitter power, but due to the tower on the transmitter antenna area in the higher mast (about 300 meters), the antenna transmitter electromagnetic wave main flap over the top of the surrounding buildings to the far side of the radiation to seek a larger service area (service radius of 70-90 kilometers), around the ground and some high-rise buildings are in the television tower radiation electromagnetic wave weak sub-flap area. But the city planning department to approve and control the height of the building around the TV tower to prevent the top of the high-rise building into the TV tower radiation strong sub-petal area, resulting in electromagnetic radiation pollution.
It is worth noting that: the gain is not high, the power is not big, but the maximum radiation field strength of the TV antenna erected at a lower height in some occasions may also be large.
Two located in the suburbs of the medium-wave broadcasting transmitter
The frequency range of medium-wave broadcasting is 531-1602KHz, most of the transmitting antenna using a pull-wire tower to radiate vertically polarized waves, generally referred to as a single tower for the non-directional antenna, double-tower for the weak directional antenna, four towers and eight towers for the strong directional antenna. Most of the energy is propagated along the ground, and a small part of the energy is propagated to the sky (dominated by ground wave propagation). In order to ensure a better radial service radius, the transmitter is generally built in the suburbs of the city. As a result of urban development, many medium-wave transmitter antennas built in the near suburbs at the beginning of the founding of the country are surrounded by the expanding urban areas, and such incidents have occurred in Beijing, Jiangsu, Fujian, Xinjiang, Guangzhou, Wuhan, Hangzhou and other cities. It affects the transmission of electromagnetic wave signals on the one hand, and on the other hand, it makes the area adjacent to the antenna become a strong field area, with field strengths ranging from dozens of v/m to hundreds of v/m, which exceeds the national standard of 40 v/m in this frequency band. Residents of the phone can not be reached, television viewing is interfered with, some houses bulbs and lamps do not need to press through the power supply is red and bright. The result is that the consumption of the radio station useful transmitter power, but also cause environmental pollution.
Three located in the suburbs of the short-wave broadcasting and communications transmitter
Short-wave transmission frequency range of 3-30MHz, short-wave broadcasting and communications is a long-distance radio propagation, antenna in the vertical plane in the direction of the maximum emission of a certain angle of elevation, the use of airborne ionosphere on the reflection of radio waves, so that the propagation of the coverage of the area in the hundreds of kilometers to thousands of kilometers, that is, often referred to as the skywave service. Along the ground propagation of electromagnetic wave depletion faster, the propagation distance is extremely short, this part of the electromagnetic wave is the secondary valve of the radiation wave. Antenna radiation field shape in the main valve of the calculated value and the measured value is relatively close to the calculated value of the sub-flap and the measured value of a larger difference.
The shortwave antenna field occupies a large area, most of which is built on rural fields (only the right to occupy the antenna tower is purchased), and if the antenna area is adjacent to the village, similar problems with medium-wave transmitters also occur. Some areas of rural economic development, the old village renovation from the original cottage into 2-6-story buildings, then the crowd is subjected to increased electromagnetic radiation, from the field strength monitoring results show that the neighboring areas of the field strength of up to 10v/m or so, and with the rise in height, the field strength enhancement. The band environmental standards for 12-40 v/m (with frequency).
Four is located in the city on the roof of high-rise residential buildings of mobile communication base station
In recent years, the rapid development of urban radio mobile communications, mobile communication networks currently include: (1) mobile telephone network (commonly known as big brother); (2) radio paging network; (3) radio trunking professional network. This type of radio communication network *** with the same characteristics are:
(1) the working frequency for ultra-short wave and decimeter band, electromagnetic wave transmission for space direct wave, the communication network by the central station, base station and user station (user machine);
(2) the larger the area covered by the radio communication network, the larger the power of the transmitter equipment at the base station or base station number is more. In order to improve the quality of communications, high-rise buildings in urban areas on the base station station more and more, in many areas, the base station antenna has been built in the high-rise residential buildings; cell phone base station antenna height, due to the cellular network continues to be split, the cellular becomes smaller, the antenna height is reduced, has been reduced from the original 50 meters or so down to 20 meters or so.
(3) built in the hot spot of the base station, due to the service area users, the base station occupies more than one carrier frequency, increasing the antenna transmit electromagnetic wave radiation.
In the urban radio communication network, the public reflected the most, the most extensive influence is the mobile phone network ("big brother" network).
Mobile phone base station electromagnetic radiation monitoring results show that the norms of scientific antennae will not generally pollute the surrounding environment sensitive buildings, because the electromagnetic wave main valve and strong sub-flap will be from the top of the surrounding buildings or gaps through, but the following cases should be prevented:
(1) base station directional antenna height is lower than that of the surrounding buildings, and the antenna main shooting direction facing the sensitive buildings closer to the distance;
(2) when the base station antenna is installed on the edge of a high-rise building, and there is a primary inclination, the antenna radiates electromagnetic waves of the vertical wave flap may hit the building antenna below the window of the residents;
(3) residential areas built on the roof of the multi-site (multiple cell phone antennas or multiple paging, trunking communications antennas) electromagnetic waves for the composite frequency field strength.
V is located in the urban area around the satellite earth station
Satellite earth station uplink transmitting power is generally between a few hundred W to several KW, the antenna elevation angle is generally between a few degrees to dozens of degrees. Due to the high transmit power, the space in front of the antenna at a certain distance height and the electromagnetic wave radiation around the antenna has a high power density; according to the antenna directionality diagram, it can be seen that there is also a fairly high irradiation dose of spurious radiation in the antenna front region and backward region, and these irradiation doses are caused by the electromagnetic wave sub-flap. The electromagnetic wave sub-flaps are the wave flaps outside the main beam.
The power density monitoring results of electromagnetic radiation on the ground near several satellite earth stations in Beijing area are as follows: the antenna effective transmitting power is about 70dBW, the antenna diameter is 9-18 meters, the antenna height is 8-10 meters, the maximum value of the antenna in front of the antenna is between 20-70 meters, the power density is 4.8 meters, and the power density is 4.8 meters, and the power density is 4.8 meters. Between the antenna diameter 9-18 meters, the antenna front maximum value appears in 20-70 meters, power density in the range of 4.8-16μw/cm2; antenna back leakage maximum value appears in the range of 10-30 meters, the power density is about 3-30μw/cm2.
Six gradually approaching the urban center of the ultra-high-voltage power lines and substations
China's power network is 500KV-220KV (or 330KV)-110KV-35KV-10KV series. 80 years ago, the high-voltage power lines (110KV-35KV) and the substations are located in the center of the city, and the power lines are located in the center of the city. Before the 80's, high voltage power lines (above 110KV) were mainly distributed in areas outside the city (or outside the moat). since the 90's, with the increase of electricity consumption in the city, the power sector to increase the construction of power equipment in the city, 110KV and 220KV high voltage cables began to be introduced into the city. Shanghai, Beijing, Tianjin and other areas in the city center have been built 110KV and 220KV high-voltage substations.
High-voltage power lines and substations deliver 50Hz industrial frequency current, which itself does not produce high-frequency electromagnetic radiation, and its main hazard is that when the delivery voltage is higher, around the conductor or substation near the generation of industrial frequency electric field and industrial frequency magnetic field, easy to produce harm to the human body. Secondly, the electromagnetic noise generated (mainly below 30MHz) will interfere with broadcasting and radio communication when it is strong. Monitoring results show that: (1) under the high-voltage power lines, 110KV double line under the range of several hundred to 2000V/m, 220KV double line tower under the 3000V/m or so, are less than the limit value of 4KV/m; 500KV line under the 5000V/m or so, more than the limit value of 4KV/m; (2) high-voltage substations, open 110KV and 220KV main transformer 1.5 meters, the I-frequency field strength as high as 2050-3200MHz. Field strength as high as 2050-3200V/m; if the whole indoor and underground substations, due to the role of building shielding, substation outdoor and substation ground IF field strength value is basically the same as the background value of the environment (below 10V/m). (3) the whole indoor and underground substation 20 meters away from the electromagnetic noise value is basically less than the limit value of 55 dBμV/m.
Seven in the urban area is widely distributed, the number of industrial, scientific, medical high-frequency equipment
"according to the requirements of industrial, scientific, medical, domestic or similar uses and design, to generate and in the local use of radio frequency Energy equipment or devices" is called industrial, scientific and medical high frequency equipment.
Industrial medical high-frequency equipment requires the use of electromagnetic energy, but does not wish to emit electromagnetic waves. This type of equipment has a strong electromagnetic oscillation source, theoretically, should have its fixed operating frequency, but the business in order to simplify the equipment, reduce costs, the oscillation source of the spectral quality is very poor (not a dedicated operating frequency), there will be a wider range of frequencies of electromagnetic radiation (or electromagnetic leakage), the surrounding environment and the formation of the operator of the harm of electromagnetic radiation.
From the high-frequency induction heating and high-frequency dielectric heating equipment monitoring results: (1) the two types of high-frequency heating equipment, 0.5-1 meters at a higher field strength, this distance for workers to operate or adjust the location of the machine, indicating that the working environment is more serious electromagnetic radiation pollution; (2) with the increase in the distance from the point of measurement, the field strength of 5 meters or so that the attenuation of a few V/m, 10 meters away or outside the work shop is generally not detected. Outside the work shop is generally not detected, indicating that industrial high-frequency equipment field strength attenuation faster. It shows that industrial high-frequency equipment electromagnetic radiation on the environment outside the plant crowd radiation impact is small; (3) industrial high-frequency equipment on the environment is mainly electromagnetic noise interference. Distance test, at a distance of 30-80 meters from the distance, different frequencies of the interference field strength values up to 56-90 dBμV/m.
Medical high-frequency equipment, mainly ultra-short-wave physiotherapists, microwave therapeutic instrument and high-frequency scalpel. Electromagnetic energy is the object of work is human, relying on electromagnetic energy to play a certain therapeutic role. But the individual field strength is high, the formation of harm to the surrounding operators, on the other hand, due to poor spectral purity caused by radio and television and communications interference. From the monitoring results can be seen: (1) its working frequency bandwidth than the industrial bandwidth, from 0.3MHz to several GHz, the power of its equipment and industrial comparison is slightly smaller, generally between dozens of hundreds of W; (2) medical equipment field strength radiation law with the industry, with the increase in the distance to the attenuation of the more rapid, generally outside the 10-meter most of them are not detected.
Eight of the rapid development of personal communication tools - cell phones (cell phones)
Mobile phones are an advanced wireless and wired relay communication tools. It is a convenient and effective means of communication in case of emergency or important matters. By 1999 there were 38 million cell phone users in the country.
Mobile phone call procedure is: voice signals into high-frequency electromagnetic waves from the handheld phone antenna radiation into the air, electromagnetic waves containing voice signals through space to the nearest cell phone base station (generally built on the roof of high-rise buildings) a channel of the communication machine, the base station to receive the signal through the fiber-optic cable or microwave to the central switching station of the mobile network, and then by the center of the station will be signaled to convert to the local telephone exchange network. Converted to connect to the local telephone exchange network (or to another base station), thus realizing the wireless and wired (or wireless and wireless) between the relay communication.
Mobile phones rely on the transmission of electromagnetic waves to transmit information, although its transmission power has been reduced from the original 3-5W to the current 0.25-2W, but due to the call from the cell phone antenna is too close to the brain (5-10 cm), long-duration calls are subjected to a long period of electromagnetic radiation. The cell phone antenna is too close to the brain (5-10 centimeters) during the call. Some cell phone calls near the antenna electromagnetic wave intensity monitoring results can be seen: most of the power density value of tens to hundreds of μw/cm2, call time maximum value of up to 1000 μw/cm2 or so. The State Environmental Protection Administration formulated the "electromagnetic radiation protection regulations" in the day 24 hours in the environment of electromagnetic radiation field field parameters in any continuous 6 minutes in the average value should be less than 40 μw/cm2. can be seen, the use of mobile phones, the local environment has more than the environmental standards of strong electromagnetic waves. The easiest way to protect is with a headset.
Nine gradually entered the family life of people with a wide variety of household appliances
Household appliances are for the daily application of electrical appliances for the family, but also can be used for industrial and agricultural production and public utilities, so it is also known as daily appliances. Its development history is relatively short, only a few decades, but its development is quite rapid. According to statistics, the production of household appliances in the earliest countries, the product range of more than 200 kinds, nearly 10,000 styles.
Household appliances can improve the production environment, reduce housework, and create favorable conditions for the socialization of daily life, improve people's standard of living; but on the other hand, if used improperly, it will also cause the deterioration of the electromagnetic environment, affecting the people's health or causing radio noise interference.
Common household appliances can be divided into air-conditioning appliances, refrigeration appliances, kitchen appliances, cleaning appliances, heating appliances, cosmetic fitness appliances, plastic and wood appliances, arts and crafts, film and television appliances, and other types of appliances.
The U.S. Environmental Protection Commission after years of research found that long-term living in the extremely low-frequency electromagnetic fields (such as 50Hz), can
lead to the occurrence of certain cancers in humans, with a variety of household appliances into the tens of thousands of households, the people exposed to contact with and exposure to the domestic appliances by the refrigerator, electric blankets and other extremely low-frequency magnetic field opportunities gradually increased.
The microwave oven as a fire-free, smoke-free, fast cooking stove, both clean and hygienic and time-saving. Microwave heating of food is the principle of microwave ovens within the microwave source (magnetron) radiation of microwaves so that the instrumentation of intermolecular friction and generate heat. In order to prevent microwave leakage, microwave ovens generally have a "triple protection measures": (1) multiple safety interlocking micro-opening device; (2) the door around the design of the infusion structure, which has the role of guiding the microwave inversion phase, microwave will be and it reverses the reflected wave offset, thus preventing microwave leakage from the door around the door; (3) the door of the observation window of the glass There is a layer of metal textile net in the sandwich, which can block the microwave penetration. Domestic and foreign household microwave oven monitoring results show that: when the power on, the microwave oven 5-10 centimeters at about 1.0-230μw/cm2 microwave leakage; 0.5 meters away from the majority of the product microwave leakage can be less than 1.4μw/cm2.
Ten traffic arteries on both sides of the electromagnetic noise
The engine ignition system is the strongest source of broadband electromagnetic noise interference. The most important reason for the interference is still the current intermixing and arcing phenomenon. Ignition produces spark current pulses and arcs with steep waveform fronts, spark current peaks up to several thousand amperes, and has an oscillating nature, whose spectrum includes the fundamental and its harmonics, and extends all the way to the X-band. In addition to the ignition system (the most significant source of interference), there are also the car's electric horn, the generator's rectifier, the battery's high-current transient on-off, and so on. Even the electric motor of the power window can produce a very narrow spike of electromagnetic interference.
From the monitoring results of electromagnetic noise on traffic arteries in Beijing and Shenzhen City, the following characteristics are observed: (1) at traffic intersections during peak traffic hours, the electromagnetic noise value is between 44-50 dBμV/m; (2) with the increase of distance, the interference field strength is basically negative logarithmic relationship to attenuation, and the attenuation law of each frequency with the distance is almost the same and the attenuation radiation is almost the same in the range of 0-30 meters. -30 meters between the maximum attenuation of the spoke; (3) from the measurement of the spectrometer to observe the automobile spark interference has a wide frequency band, from a few MHz extends to more than 300 MHz, but in the range of 10 - 25 MHz has a large interference field strength; (4) small car spark interference is small, trucks and motorcycles spark interference is the largest, the frequency and the field strength of the inverse relationship is not monotonous, which is related to a variety of vehicle points The relationship between frequency and field strength is not monotonous inversely proportional to the type of ignition system with a variety of vehicles, driving speed, load and vehicle wear and tear, and other factors; (5) from the spectrometer to observe 50 meters within the peak car interference is enough to interfere with the effect of radio and television viewing, so it is recommended that in the urban planning, residential buildings are best from the road more than 50 meters for good.
Third, do a good job in the protection of the urban electromagnetic environment
21st century, mankind will enter the information society, the urban electromagnetic environment will be more complex. Suggestions for urban electromagnetic environmental protection should do the following work:
A widely publicized and implement the national "electromagnetic radiation protection regulations" and "electromagnetic radiation environmental protection management approach". Construction projects related to electromagnetic radiation should fulfill the construction project environmental protection procedures, to meet the relevant national environmental protection standards, so that the urban electromagnetic environment in an orderly manner.
Second, electromagnetic radiation and electromagnetic environmental protection science publicity. Electromagnetic radiation due to invisible, can not touch, but also can not hear, smell, so it is difficult to be perceived, the masses are very strange to it, and it is easy to have doubts. If there is an antenna near someone's home, the residents will feel that they are living in the radiation, but in fact, if the antenna is set up reasonably, it has no effect on the surrounding environment; some of the reports on electromagnetic radiation are not very objective, but only sensationalized that electromagnetic radiation is harmful, but how much intensity is harmful is not written clearly, which is easy to make the masses to have a misunderstanding. We should be electromagnetic radiation science information publicity, so that the masses understand the basic knowledge and characteristics of electromagnetic waves, that is, not afraid of electromagnetic waves, but also scientific protection against electromagnetic radiation pollution.
Third, we should carry out the management of the urban electromagnetic environment and electromagnetic radiation protection of scientific research. Urban electromagnetic wave energy density is growing, but the urban airspace in the end how much field strength and power density capacity, there is no exact statement at home and abroad. Environmental protection management objectives of the task is, that is, to prevent electromagnetic radiation pollution, protect the environment, protect public health, but also to promote the development of legitimate practices accompanied by electromagnetic radiation.