What Is an Electromagnetic Wave?

Electromagnetic wave is an oscillating particle wave emitted in the space by an electric field and a magnetic field that are in phase and perpendicular to each other. It is an electromagnetic field that propagates in the form of waves and has wave-particle duality. Electric and magnetic fields that oscillate in phase and are perpendicular to each other move in the form of waves in space, and their propagation direction is perpendicular to the plane formed by the electric and magnetic fields. The rate of electromagnetic waves in a vacuum is fixed at the speed of light. See Maxwell's equations.

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From a scientific perspective, electromagnetic waves are a type of energy.

Electromagnetic field includes two aspects of electric field and magnetic field, and its characteristics are expressed by electric field strength E (or electric displacement D) and magnetic flux density B (or magnetic field strength H). According to Maxwell's theory of electromagnetic fields, these two parts are closely related. A time-varying electric field causes a magnetic field, and a time-varying magnetic field also causes an electric field. When the field source of the electromagnetic field changes with time, the electric field and the magnetic field mutually excite each other, causing the electromagnetic field to move and form electromagnetic waves. The propagation speed of electromagnetic waves is equal to the speed of light. In free space, it is c = 3 × 10 ^ 8m / s. The travel of electromagnetic waves is also accompanied by the transmission of power.

Electromagnetic field is a special form of matter, which has the main properties of general matter, such as mass, energy, momentum, etc. Objectively, there is always a unified electromagnetic field that has nothing to do with the observation conditions. Dividing it into an electric field and a magnetic field is opposite, and it is related to the test conditions.

Spherical, cylindrical, and plane waves For electromagnetic waves that change sinusoidally with time, according to the fact that the isophase plane (ie, the wave front) of the electric field intensity E and the magnetic field intensity H is spherical, cylindrical, or plane, the electromagnetic wave has a spherical surface Wave, cylindrical and plane waves.

Electromagnetic waves are

Electromagnetic wave

The energy of electromagnetic waves is

Arranging these electromagnetic waves in order of wavelength or frequency, is

In a safe electromagnetic environment, if you have long imagined that electromagnetic waves will cause damage to your own health, it will inevitably cause psychological problems such as anxiety, fear, and boredom due to excessive mental stress, and then affect endocrine until your own health. Therefore, it is necessary to correctly understand the causes of electromagnetic waves and their possible harm, and how to reduce or avoid the effects of electromagnetic waves common in life.

As long as it is not at absolute zero (

Definition of electromagnetic wave

Electromagnetic wave pollution, also known as electromagnetic pollution or radio frequency radiation pollution. It is characterized by the field force of the electromagnetic field, and is closely related to the nature, power, density, and frequency of electromagnetic waves. Due to the widespread application of electronic technology, the rapid development and popularization of radio broadcasting, mobile phones, televisions, and microwave technologies, the power of radio frequency equipment has doubled, and electromagnetic radiation on the ground has increased significantly. Has reached a level that can directly threaten human health. Electromagnetic pollution is an invisible pollution that has become a public hazard that people pay close attention to. The impact on human society has attracted attention from countries around the world and is listed as one of the environmental protection projects.

Electromagnetic wave classification

Natural pollution

Natural electromagnetic wave pollution is caused by certain natural phenomena. The most common is lightning. In addition to direct damage to electrical equipment, aircraft, buildings, etc., lightning can also cause severe electromagnetic interference in a very wide frequency range from thousands to hundreds of MHz in a wide area. Volcanic eruption, earthquakes, and magnetic explosions caused by sunspot activity all produce electromagnetic interference. The interference of natural electromagnetic wave pollution on short-wave communication is extremely serious.

2. Man-made pollution

Man-made electromagnetic wave pollution includes:

Pulse discharge. For example, a spark discharge generated when a high-current circuit is cut off has a large transient current and generates a strong electromagnetic field. It is essentially the same as a thunderbolt, but with a smaller area of influence.

Power frequency alternating electromagnetic field. For example, the electromagnetic field near high-power motors, transformers, and power transmission lines does not radiate outward in the form of electromagnetic waves, but it will cause serious electromagnetic interference in the near field area.

Radio frequency electromagnetic radiation. For example, the radiation of various radio frequency equipment such as radio broadcasting, television, and microwave communications has a wide frequency range and a large impact area, which can endanger workers in the near field. Radio frequency electromagnetic radiation has become a major factor that pollutes the environment with electromagnetic waves.

Electromagnetic wave propagation

1 Broadcasting and TV transmitting equipment, mainly related to radio broadcasting communication, is the transmitting station and relay station of radio and television in various places.

2 Communication radar and navigation transmitting equipment communication, including shortwave transmitting station, microwave communication station, ground satellite communication station, mobile communication station.

3 Industrial, scientific research, medical high-frequency equipment. This type of equipment converts electrical energy into heat or other energy for use, but is accompanied by the generation and leakage of electromagnetic radiation, causing environmental pollution in the workplace.

Industrial electromagnetic radiation equipment: mainly high-frequency induction heating equipment, such as high-frequency quenching, high-frequency welding and high-frequency furnaces, high-frequency melting equipment, etc., and high-frequency dielectric heating equipment, such as plastic heat sealing machines, high-frequency drying processors , High-frequency dielectric heating linkage.

Medical electromagnetic radiation equipment: mainly short-wave, ultra-short-wave physiotherapy equipment, such as high-frequency physiotherapy machines, ultra-short-wave physiotherapy machines, ultraviolet physiotherapy machines, etc.

Scientific research on electromagnetic radiation equipment: mainly electronic accelerators, various ultrasonic devices, electromagnetic stoves, etc.

4 Electromagnetic radiation interference of transportation system, including: electrified railway, light rail and electrified railway, tramcar, non-rail

Tram and so on.

5 Electromagnetic radiation of power systems. High-voltage power lines include overhead power lines and underground cables. Substations include power plants and transformer stations.

6 Household appliances electromagnetic radiation, including microwave heating and emission equipment, including computers, monitors, televisions, microwave ovens, wireless telephones, etc.

The electromagnetic wave pollution in family life, which is closely related to people's daily life, refers to various electronic living products, including air conditioners, computers, televisions, refrigerators, microwave ovens, karaoke machines, VCD machines, stereos, electric blankets, mobile phones Etc., the electromagnetic waves of different wavelengths and frequencies generated during normal work interfere with, affect and harm humans.

The main hazards of electromagnetic waves

Because electromagnetic waves are colorless, odorless, invisible, and traceless, and pollution has neither any feeling nor ubiquity, it is called "electronic waste" or "electronic radiation pollution" by scientists. Xiaoyan. It is mainly manifested in the following three aspects:

(1) Affects the normal operation of electronic equipment

Modern technology is more and more inclined to use large-scale and ultra-large-scale integrated circuits. The density of circuit components is extremely high. In addition, the current used is microcurrent, so that the signal power and noise power are almost the same. Parasitic radiation may cause malfunction of electronic systems or electronic equipment. Or obstacles. On the other hand, the rapid development of modern wireless communications industry, various transmission towers make the airwaves crowded, which seriously affects normal business in all aspects. Beginning in September 1996, incidents involving interference from radio paging stations in aviation communications frequencies above 1.30 MHz at Beijing Capital Airport occurred frequently. At 8:15 am on February 20, 1996, the air-to-air channel was severely disrupted, and 10 aircraft had to circle and wait in the air, causing the departing aircraft to have a flight time of 5 to 15 minutes. The same incident happened frequently in other parts of the country. Where people are accustomed to thinking that birds are flying high, electromagnetic wave interference has brought great harm to people.

(2) Scientific research and facts show that electromagnetic waves are also very harmful to the human body

The harm of electromagnetic radiation to the human body is caused by the energy of electromagnetic waves. According to relevant experts, China s mobile power

The transmission frequency of the words is between 800 and 1000 MHz, and its radiation dose can reach 600 microwatts, which is more than 10 times higher than the national standard. Excessive electromagnetic radiation can cause human nervous breakdown, decreased appetite, palpitations, chest tightness, dizziness, etc. "Electromagnetic wave allergy" can even cause brain tumors. There are many examples of the harm caused by electromagnetic wave pollution to the human body, but the extent of the impact is related to the intensity of the radiation and the length of accumulation. It has not been reflected to a large extent at present, so it has not attracted widespread attention. Relevant research shows that the pathogenic effect of electromagnetic waves increases with the increase of the magnetic field vibration frequency, and the frequency exceeds 100,000 Hz, which can cause potential threats to the human body. Working and living in this environment for too long, the human body is disturbed by electromagnetic waves, which causes the original electric field of molecules in the body tissue to change, resulting in disorder of the body's ecological balance. Some people who have been exposed to strong or prolonged electromagnetic wave radiation have had morbid manifestations, which are mainly reflected in the nervous system and cardiovascular system. Such as fatigue, memory decline, insomnia, easy excitement, menstrual disorders, chest tightness, palpitations, white blood cells and thrombocytopenia, or low, immune function and so on.

(3) Risk of explosion due to explosives or explosive mixtures

Some tall metal structures can generate spark discharges due to high frequency induction under certain conditions. This kind of discharge not only gives people different degrees of electric shock, but also can detonate dangerous goods and cause catastrophic results. This is an issue that needs to be paid much attention to by explosives production enterprises.

(4) Electromagnetic radiation is one of the main causes of cardiovascular disease, diabetes, and cancer mutations

(5) Electromagnetic radiation will cause direct damage to the human reproductive system, nervous system and immune system

(6) Electromagnetic radiation is one of the inducing factors that cause pathological changes such as abortion, infertility and teratology of pregnant women

(7) Excessive electromagnetic radiation directly affects the development of children's body tissues and bones, leading to decreased vision and hematopoietic function of the liver, and severe cases can cause retinal detachment

(8) Electromagnetic radiation can reduce male sexual function and female endocrine disorders.

Electromagnetic wave pollution pathway

There are two ways of electromagnetic wave propagation:

One is conducted interference, which is the interference caused by the current traveling along the power line;

The other is radiation interference, which is caused by the emission of electromagnetic waves from the source to the surrounding space.

In order to prevent and suppress electromagnetic wave interference, technical methods such as reasonable design of circuits, filtering, and shielding are mainly used. Reasonably designing the circuit is to arrange the components and arrange the wiring reasonably in a small space, which can weaken the parasitic electromagnetic coupling and suppress electromagnetic interference. A filter is a line consisting of a resistor, an inductor, and a capacitor. This network can allow signals of certain frequencies to pass, while preventing signals of other frequencies from passing. Correctly designing and installing filters can reduce electromagnetic interference to a minimum. Shielding technology has been widely used as a basic means to suppress electromagnetic wave radiation. Purpose of shielding

It is to limit the radiant energy to a specific area, or to prevent the radiant energy from entering another specific area. Shielding materials are the key to high and low shielding efficiency. Recently developed wave absorbing materials have been introduced, which will contribute to the development of clean space for human beings. In addition to using the above-mentioned technical methods to suppress electromagnetic radiation pollution, other methods can be used to reduce its harm, such as prohibiting the establishment of high-power wireless paging stations around the airport, and taking good shielding and protection measures for workers who frequently come into contact with RF equipment.

In short, with the development of science and production, the harm of electromagnetic radiation pollution has a tendency to deteriorate. It is of great practical significance to study the harm and protection of electromagnetic wave pollution.

Electromagnetic wave penetration

Because electromagnetic waves have wave-particle duality, the wavelength is inversely proportional to the photon energy. When the wavelength is shorter, the photon energy is greater, and the penetrating power is stronger. For example, high-energy X-rays can penetrate almost all non-metallic objects, even thin aluminum; and gamma-rays can penetrate most metals. Certain heavy metals can block electromagnetic waves, such as lead.

Electromagnetic wave related cases

Even more than 20 years ago, after domestic microwave ovens became popular in the United States, some patients with pacemakers often felt uncomfortable, and some pacemakers even failed to stop suddenly. Later, the research of scientists made its truth known to the world because of "electromagnetic wave pollution".

A few years ago, the famous Russian chess master Nikola Kedkov played against a computer. After winning 3 games in a row, he was suddenly overwhelmed by the powerful current released by the computer. Investigations have confirmed that this is not a computer hardware leak, nor a software designed killing program, and the cause of death is invisible electromagnetic waves.

It is reported that workers who operate more than 6 hours in front of a computer every day are susceptible to a condition called "VOT". This condition refers to a general term for diseases that occur in certain parts of the body by watching video terminals for a long time. Its main symptoms are: visual dysfunction; neck, shoulder, and wrist dysfunction; autonomic dysfunction; etc .; In addition, it can cause women's disorders such as irregular menstruation, abortion and other skin diseases. The reason is also caused by electromagnetic wave radiation.

Mobile phones and walkie-talkies are also a source of high-frequency electromagnetic wave pollution, and electromagnetic waves are emitted every time a call is made. Scientists believe that the intensity of electromagnetic wave radiation of mobile phones generally exceeds the specified standard by 4 to 6 times, and individual types even exceed nearly a hundred times. China's Electromagnetic Radiation Test Center and Xiamen Changqingyuan Radiation Protection Research Institute have confirmed after two years of tracking and testing that the mobile phones currently used in our country will cause radiation harm to the human body.

Prevention of electromagnetic wave pollution

There are many easy-to-operate measures to reduce the harm of electromagnetic wave pollution.

There are two general principles:

First, because it is necessary to work away from electromagnetic wave emission sources, shielding and protection must be adopted;

Second, try to increase the distance between the human body and the emission source.

Because the impact of electromagnetic waves on the human body is closely related to the size of the transmitted power and the distance from the source, its harmful process

The degree is directly proportional to the transmitted power and inversely proportional to the square of the distance. Taking mobile phones only as an example, although its transmitting power is only a few watts, because its transmitting antenna is close to a person's head, the actual radiation intensity it receives is equivalent to a broadcast of several hundred kilowatts away from tens of meters. The radiation intensity to which the radio transmitting antenna is exposed. Fortunately, people use it for a short period of time, and will not show obvious harmful symptoms for a while; but if used for a long time, the symptoms caused by radiation will gradually be exposed. Excessive radiation will cause abnormal cell activity and division, and cause cancer Possible.

In view of this, we should consciously take measures in daily life to reduce the harm of electromagnetic wave pollution. For example, people working in places with high electromagnetic wave intensity such as computer rooms should pay special attention to rest during work. They can be appropriately moved outdoors away from the electromagnetic field. When using mobile phones, keep the antenna as far away from the human body as possible, especially the head. And try to reduce the time of each call as much as possible; household appliances should not be placed in a centralized way, and the distance for watching TV should be kept at 4 ~ 5 meters, and pay attention to opening windows; After the blanket is warmed up, you should cut off the power when you fall asleep. Children and pregnant women should not use electric blankets; usually eat more fresh vegetables and fruits to enhance the body's ability to resist electromagnetic wave pollution.

First, keep your distance. The distance from the TV should be the screen size multiplied by 6, the distance from the microwave oven should be 2.5 to 3 meters, and it is generally regarded as a safe area beyond 0.5 thousand volts / meter.

Second, reduce exposure. People who use the computer regularly should take a quarter of an hour for each hour of work, and work at most every week

After 32 hours.

3. Improve the environment. Pay attention to air circulation, temperature and humidity should be moderate, household appliances should not be placed in the bedroom.

Fourth, personal protection. Pregnant women, children, frail people, people who are allergic to electromagnetic wave radiation, and people who have been exposed to electromagnetic wave pollution for a long time should choose suitable protective equipment.

Five, use less mobile phones. To minimize the use of mobile phones, walkie-talkies, and cordless phones, you must use short words when using them; do not hang your phone on your body often.

6. Use less electric blankets. The electromagnetic wave pollution of the electric blanket is serious. It is harmful to the human body when it is powered on for a long time. When it is necessary to use it in cold weather, it is recommended to cut off the power immediately after heating the quilt to reduce electromagnetic wave pollution.

7. Use shields to reduce electromagnetic wave pollution. For facilities that generate electromagnetic pollution, shields that shield, reflect, or absorb electromagnetic waves, such as copper, aluminum, steel plates, and polymer films, can be used.

8. According to the characteristics of electromagnetic wave attenuation with distance, in order to reduce the harm of electromagnetic waves to residents, workplaces and facilities that emit large electromagnetic power and may produce strong electromagnetic waves should be made, such as television stations, radio stations, radar communication stations, and microwave transmission stations. As far as possible, it should be located in remote suburban counties or high-lying areas far from residential areas. Facilities, such as substations, which must be located in the city, adjacent residential areas, and areas where residents often move, should maintain a certain safety protection distance from the residential area to ensure that their boundaries meet the requirements of environmental electromagnetic wave health standards. At the same time, the electromagnetic radiation source needs to be selected from materials made of copper, aluminum, steel and other metal wires or polymer films that can shield, reflect or absorb electromagnetic waves, to limit the electromagnetic radiation energy to the specified space.

Nine, high-voltage, especially ultra-high-voltage transmission lines should be kept away from residential areas, schools, sports fields and other densely populated areas. When using a computer, a low-radiation display should be selected, and the distance between the human body and the front of the display should be no less than 75cm, and the side and back should be no less than 90cm. It is best to install a shielding device.

10. The density of mobile communication base stations should be strictly controlled to ensure that the antennas of various mobile communication transmitting base stations installed in urban areas are higher than surrounding buildings. Transmitting antennas must not be established within a certain range around buildings such as kindergartens, school buildings, and hospitals.

11. In order to reduce the electromagnetic pollution and harmful effects in the home, the room should be ventilated frequently to keep the indoor air flowing. Use household appliances scientifically: For example, when watching TV or home theater, listening to the combined sound, you should keep a long distance and avoid turning on various electrical appliances at the same time; the use of a computer or electronic game console should not be too long.

12. When using a mobile phone, try to reduce the talk time as much as possible. The top of the mobile phone antenna should be as far away from the head as possible, and the antenna should be extended as much as possible. Add a headset to the mobile phone.

13. In addition, you can take a certain amount of vitamin C every day or eat more fresh vegetables rich in vitamin C, such as pepper, bell pepper, toon, cauliflower, spinach, etc .; eat more fresh fruits such as citrus, jujube and so on. Diet should also pay attention to eat more foods rich in vitamins A, C and protein, such as tomatoes, lean meat, animal liver, bean sprouts, etc .; often drink green tea. These dietary measures can, to a certain extent, play an active role in preventing and reducing the harm caused by electromagnetic radiation to the human body.

14. Electromagnetic wave radiation is a new type of environmental pollution that has only been recognized by people for nearly three to four decades. People are still in the stage of understanding and research on electromagnetic radiation. Because it is invisible, intangible, and hard to detect, it is easy to cause people to doubt. In addition, some reports on electromagnetic radiation are not objective and scientific, leading to unnecessary misunderstandings and panics. In general, to determine whether electromagnetic radiation causes pollution to the living environment, comprehensive consideration should be given to the electromagnetic wave radiation intensity, the main radiation direction, the distance from the radiation source, and the duration. Therefore, while strengthening electromagnetic protection, we should also adopt a scientific attitude to the problem of electromagnetic wave pollution, take an objective analysis, and take it seriously. We must not let others go. The irresponsible blind exaggeration has caused confusion in people's understanding. Of course, with the development of science and technology, people's understanding of electromagnetic wave pollution and its harm will gradually deepen, and many mysteries will eventually be revealed.

Electromagnetic wave related regulations

Electromagnetic environment standards and related regulations. In order to control the pollution of electromagnetic waves to the environment in modern life and protect people's health, the Ministry of Health of China issued the "Environmental Electromagnetic Wave Health Standard" (GB9175-88) on December 22, 1989, which stipulates the limit values of the electromagnetic wave intensity in residential areas: Medium and short waves should be less than lOV / m, ultrashort waves should be less than 5V / m, and microwaves should be less than 10W / cm ² . Relevant departments in China have also formulated the "Standard for the Radiation Health Protection Distance of TV Towers", and the State Environmental Protection Administration has also promulgated the "Administrative Measures for Environmental Protection of Electromagnetic Radiation".

In response to the development of mobile communications, the Beijing Municipal Environmental Protection Bureau promulgated the "Beijing Mobile Communications Construction Project Environmental Protection Management Regulations" (trial), the first in the country to regulate electromagnetic pollution, on February 17, 2000 to regulate mobile communication stations. (Station) construction and operation to prevent it from causing electromagnetic pollution to the environment. The regulation specifies that mobile communication stations (stations) capable of generating electromagnetic radiation must perform environmental protection approval procedures before going through construction, and also undergo environmental protection acceptance approval. After monitoring by environmental protection departments, the local power density complies with the State's "Electromagnetic Radiation Protection Regulations" The frequency in the range of 20 MHz to 3000 MHz and the power density of the exposure-derived limit is 40 W / cm ² before it can be officially put into use. If it exceeds this standard, it must be deactivated or rectified; construction of cellular mobile communications The user density distribution should be predicted in front of the base station, and the best frequency reuse method should be used to minimize the number of base stations. When building mobile communication stations (stations) on residential buildings, the building property unit or property management unit must obtain the opinions of the residents beforehand. ; The minimum allowable height of radio paging communication and trunking communication antennas must not be lower than 40m, while the outdoor antennas of cellular mobile communication base stations are generally not lower than 25m, and the transmitting antennas are within 50m of the main radiation direction and within 30m of the non-main radiation direction. Buildings such as hospitals, kindergartens, schools, houses, etc. that are higher than the antenna; the construction unit should install electromagnetic Fire warning signs.