(This article was originally written by Devymex, please indicate the author Devymex)
People are often worried that the radiation emitted by mobile phones will be harmful to health. Some people think it will affect fertility, others think it will affect fetal health, and others think it will induce brain cancer. In recent years, there have been many pseudo-scientific works on the Internet discussing the radiation hazards of mobile phones, which have aggravated people's concerns. Starting with the analysis of electromagnetic waves, this paper briefly discusses the principles of ionizing radiation and non-ionizing radiation and their various effects, briefly analyzes the penetration of electromagnetic waves, lists the understanding of electromagnetic waves by authoritative institutions or organizations around the world, and summarizes and analyzes whether it will affect health at the end of the article. Let more people clearly understand that mobile phone radiation is harmless and stop worrying about it.
When people use mobile phones to communicate, mobile phones will send voice or other data signals to mobile base stations in the form of electromagnetic waves (radio waves), and also receive electromagnetic waves from mobile base stations. These electromagnetic waves are commonly known as "cell phone radiation". Therefore, to understand the radiation of mobile phones, we must first talk about electromagnetic waves.
Electromagnetic wave is a kind of energy, just as people have been living in the air but their eyes can't see the air, so people can't see the ubiquitous electromagnetic wave. Electromagnetic wave is such a "friend" that human beings have never met. Electromagnetic wave is a form of movement of electromagnetic field. Electricity can produce magnetism, and magnetism can also bring electricity. The changing electric field and magnetic field constitute an inseparable unified field, which is electromagnetic field. The changing electromagnetic field propagates in space to form electromagnetic waves, so electromagnetic waves are often called electric waves. 1864, British scientist J.C. Maxwell established a complete electromagnetic wave theory on the basis of summarizing previous studies. He concluded that electromagnetic waves exist and concluded that electromagnetic waves and light travel at the same speed. 1887, German physicist H.R. Hertz confirmed the existence of electromagnetic waves through experiments. After that, many experiments were carried out, which not only proved that light is electromagnetic wave, but also found more forms of electromagnetic wave. Their essence is exactly the same, but there are great differences in wavelength and frequency. According to the order of frequency from high to low, the common electromagnetic waves are: long wave
50Hz~5KHz: power lines, substations, induction cookers, hair dryers, computers, televisions, washing machines, electric blankets, air conditioners and desk lamps;
5 khz ~ 500 MHz: FM broadcasting, AM broadcasting, broadcasting, TV signals, walkie-talkies;
500 MHz ~ 50 GHz: mobile phone, radar, microwave oven, GPS, satellite communication;
50 GHz ~ 2.4 PHZ: sunlight, light, infrared ray, oven heat pipe, steelmaking electric furnace;
Above 2.4 Hz: extreme ultraviolet, X-ray and nuclear radiation.
(Hz is "Hertz", the unit of frequency, indicating the number of times electromagnetic waves vibrate in one second. 1KHz= 1000Hz，MHz= 1000KHz， 1 GHz = 1000hz， 1hz = 1000 GHz = 1000hz， 1PHz= 1000GHz)
According to quantum theory, electromagnetic wave can be regarded as photon flow, and its effects can be divided into "ionizing radiation" and "non-ionizing radiation". According to the wave-particle duality of light, the higher the frequency of electromagnetic wave, the more significant the particle properties, and the lower the frequency, the more significant the fluctuation. When electromagnetic waves with high enough frequency transmit extremely high energy to other substances, photons may dissociate electrons of atoms or molecules in the substance, so that the substance is full of charged ions. This effect is called "dissociation", and the electromagnetic wave that causes this phenomenon is called ionizing radiation. Each substance has a specific critical ionization frequency. When the frequency of electromagnetic wave is lower than this critical value, no matter how strong the intensity is, it is impossible to ionize the substance.
If ionizing radiation is generated on biological tissues, cellular substances will ionize and compete with the main components in cells (such as protein, nucleic acids, enzymes, etc.) for charge. Once the atoms in these substances lose charge, the molecular structure will be unstable and new ions will be formed. Some ions will destroy the cell structure where the ions are located through chemical reactions. If the genetic material in the nucleus is destroyed (gene mutation), the cell may become an infinitely proliferating cancer cell.
Free radiation is common in nuclear power plants. People use the "decay" of radioactive substances such as uranium and plutonium to generate heat energy and convert it into electric energy. Decay usually emits three kinds of rays: alpha ray (α), beta ray (β) and gamma ray (γ). Alpha-rays are helium nuclear currents, and beta-rays are electron currents, neither of which are electromagnetic waves. Gamma ray is a strong electromagnetic wave, which is harmful to human body. When an accident occurs in a nuclear power plant or an atomic bomb explodes, a large amount of radioactive materials will be dispersed in the air, constantly emitting gamma rays, endangering life and health.
Electromagnetic waves with a frequency lower than that of visible light (the lower limit is about 400 Hz) have almost no ionization effect, and these electromagnetic waves are called non-ionizing radiation. The energy of this radiation is far from enough to break the chemical bonds of living beings and will not produce free ions harmful to human body. Therefore, there are essential differences between non-ionizing radiation and ionizing radiation, and their biological effects are completely different. Non-ionizing radiation can be divided into the following three types: 1. Light radiation with very small wavelength, such as near ultraviolet, visible light and infrared, can produce electron excitation effect; 2. Electromagnetic waves with smaller wavelength such as microwave and high frequency radio frequency will induce current and produce thermal effect; 3. Electromagnetic waves with large wavelengths such as low-frequency radio frequency, alternating frequency and electrostatic field (direct current field) rarely have any side effects on objects.
The excitation effect will induce current on the surface of the object, which will make the object heat up. Its generation depends on the frequency of radiation, the size of contact and the direction of radiation. The electromagnetic wave power used for communication is very low, and it will not make the object heat. High-power non-ionizing radiation such as sunlight, high-power lamps and electric ovens will obviously heat objects, but as long as the human body does not receive too much energy in a short time, the physiological tissue can be adjusted. Long-term exposure to high-power non-ionizing radiation will only cause burns, but will not cause cumulative damage (such as cell canceration). Microwave ovens heat food through the thermal effect of electromagnetic radiation. Its working principle is to emit electromagnetic waves with the frequency equivalent to that of water molecules, so that the water molecules vibrate. Under strong vibration energy, the water molecules rub against each other to generate heat, thus heating food with moisture. The door of microwave oven adopts special structure and material to ensure that electromagnetic radiation will not leak, so it is safe to use microwave oven.
Electromagnetic wave will also be shielded, because electromagnetic wave is a kind of shear wave, which has the general characteristics of shear wave: 1. The higher the frequency, the shorter the wavelength; 2. The shorter the wavelength, the easier it is to be blocked by obstacles, and the longer the wavelength, the easier it is to bypass obstacles or diffraction. Except for some long-wavelength electromagnetic waves used in broadcasting communication, ordinary electromagnetic waves will not have obvious diffraction effect. These short-wave electromagnetic waves can only propagate through reflection (such as short wave) and penetration (such as microwave). Short wave propagates through the reflection of the atmospheric ionosphere. The degree and effect of penetration also depend on the frequency of electromagnetic wave and the characteristics of medium. Generally speaking, the higher the frequency, the stronger the penetration ability of electromagnetic waves. However, for the same medium, the penetration of electromagnetic waves is sometimes not directly proportional to its frequency, which is related to the nature of the medium itself. According to the principle of quantum mechanics, ultra-high frequency electromagnetic waves such as X-rays and gamma rays are more granular, so they can penetrate most objects. It is for this reason that X-rays are used to examine internal lesions in hospitals and γ-rays are used to inspect industrial workpieces. The dose of X-rays used in hospitals is very small, and the ionization effect is not enough to harm the human body. )
According to the definition of International Institute of Electronics and Electrical Engineers (IEEE), electromagnetic waves with frequencies between 0.3 GHz and 300 GHz are called microwaves. Microwave also has a certain penetration, but it is relatively weak. For human body, the penetration depth and wavelength of microwave are in the same order of magnitude. According to the experimental data, the actual penetration depth of microwave source with frequency of 9 15MHz to human body is 5 ~ 6 cm, and that of microwave source with frequency of 2450MHz is 2 ~ 4 cm. Therefore, microwave thermal radiation is often used to treat superficial tissues in medical technology, thus alleviating the pain of surgical patients.
In today's society, microwave is widely used and plays an increasingly important role in information technology, communication, medical treatment, military affairs, surveying and mapping, exploration and other fields. The microwave wavelength of domestic microwave oven is 122 mm, and the corresponding frequency is 2.450GHz. The communication frequency of civil mobile phones is between 0.8 GHz and 2. 1 GHz, all of which belong to microwave. The difference is that in order to heat food, microwave ovens must emit up to 2000 watts of microwave, while mobile phones rarely emit 2 watts. There are many kinds of cell phone signals at present. Common mobile communication protocols are GMS, CDMA and WCDMA, and their microwave frequency bands are widely distributed, and their settings are different all over the world. Common ones are 800MHz, 900MHz, 1800MHz, 1900MHz, 2 100MHz. Of course, many mobile phones now support Bluetooth and 802. 1 1 protocol. The radiation frequency of Bluetooth is 2.4GHz ~ 2.48 GHz, and 802. 1 1 protocol usually has two working bands, 2.4GHz and 5GHz, which are higher than the frequency of ordinary GSM signals, but these are all microwaves. Some mobile phones also support infrared protocol, and the transmission power is equivalent to that of TV remote controller.
Many international organizations have formulated various standards to limit electromagnetic radiation, but most of these standards are very common. For example, the SAR value standard stipulated by ICNIRP is 2w/kg (watt /kg) weight, which has been adopted by most European countries. But so far, there is no exact scientific evidence to prove that radiation exceeding ICNIRP limits will affect human health. Even more demanding is TCO certification, which is the safety and environmental protection standard for electronic equipment formulated by the Swedish Professional Employees Union. There are several standards for the development of displays, such as TCO'92, TCO'95, TCO'99, TCO'0 1, TCO'03, TCO'05, etc. TCO'0 1 stipulates that under the strongest signal, the radiation received by biological tissues per kilogram weight shall not exceed 0.8 W, and the biological tissue cube of 10 g shall be taken as the standard when testing, that is to say, the SAR value specified in TCO'0 1 is 0.8w/kg. The strongest electromagnetic radiation of mobile phone is equivalent to this. According to statistics, the SAR value of Nokia N95(RM-320) is 0.47w/kg, that of Nokia E70(RM- 10) is10/w/kg, and that of Motorola V9 is 0.62w/kg.
In recent years, our government and industry also organized experts to demonstrate the safety of microwave radiation, and formulated a set of national standards and laws and regulations. Considering the population density and other factors, the current electromagnetic radiation protection standard (GB 8702-88) is 40 microwatts /cm2, which is stricter than that of industrialized countries in Europe and America. For example, the standard issued by US 1982 is 3000 MW /cm2, and that of EU is 450 MW /cm2. Moreover, in China, only devices that meet safety standards can access the network, and operators will strictly implement relevant national standards. From the user's point of view, the network planning of mobile base stations will strictly optimize the coverage design to ensure the safety of residents near the base stations.
Experiments show that electromagnetic waves travel quickly in the air. The test shows that the power density in front of the antenna of a high-power base station with transmission power of 20w is 0.6 MW/ m2 (1w =1x106 MW), which is far lower than the national standard of 40MW/ cm2. Secondly, electromagnetic waves will be attenuated by 6 decibels when passing through a general brick wall, and by about 20 decibels when passing through a wall with steel bars. Therefore, when the GSM base station antenna is built on the roof of a common house (the height of the base station antenna of China Mobile is between 35 and 55 meters), the residents in the house are absolutely safe. Moreover, the electromagnetic wave of the base station perched on the roof radiates horizontally, and the intensity in the vertical direction is almost zero, so the residents downstairs are radiation dead corners, which will not affect their health.
Many experiments, investigations and studies have been carried out on microwave radiation all over the world. The following are the opinions expressed by some authoritative organizations or organizations.
World Health Organization (WHO): Exposure of human body to extremely low frequency electromagnetic waves will not produce physiological effects.
Ota: Many experimental results show that exposure to electromagnetic waves has no effect on living things.
National Radiation Protection Committee (NRPB): The intensity of radio waves is not enough to destroy the human genome (DNA) and will not cause cancer.
Southern California Electric Power Company (SCE): A survey of 362,265,438+0 employees showed that although these employees were exposed to much more electromagnetic waves than ordinary people, the overall respondents had the same incidence of leukemia, brain tumor and cancer as the general public, and there was no higher tendency.
The Federal Communications Commission (FCC) and the Institute of Electronic and Electrical Engineers (IEEE) began to support some retrospective studies in the 1990s, and issued a statement: Up to now, there is no strong scientific evidence to prove that non-ionizing electromagnetic waves used routinely will cause harm to human body.
DOL: There is no conclusive evidence to support that "exposure to extremely low frequency electromagnetic waves emitted by household appliances, cables and monitors will be harmful to health."
1994, the Swedish National Electric Safety Authority (NENB) published a pamphlet on electromagnetic field information, indicating that it is not yet possible to confirm whether the magnetic field has an impact on human body.
Bell Laboratories declared in 1995 that even under the maximum power limit of various base stations, the electromagnetic wave power within the accessible range of people near the base stations is at least 687 times less than various safety regulations, so the public need not worry at all.
National Research Council (NRC): After counting more than 500 different topics in the past 17 years, the organization said that there is no obvious and credible evidence that electromagnetic waves emitted by base stations will cause harm to surrounding residents, and there is no significant difference between local residents in cancer incidence, female productivity, baby's growth and learning ability and other regions.
There are also many related experiments and studies in China. In the paper "Effect of Low-power Microwave on Sperm Malformation and Micronucleus Rate of Polychromatic Cells in Bone Marrow of Rats" published by journal of third military medical university in 2003 (the authors are Sun Huaming, Wu Xinan and Cao Jia), it is pointed out that rats will not cause obvious genetic damage after being irradiated by low-power microwave simulating the radiation intensity of mobile phones.
To sum up, we can draw a conclusion that under the current standards, the radiation emitted by mobile phones produced by major mobile phone manufacturers and base stations established by telecom operators is harmless to human body. Microwave used for human communication has been born for decades, but no evidence has been found worldwide to prove that this electromagnetic wave will have an impact on human health.