1, the radiation band
When it comes to radiation, we naturally think of nuclear leaks and nuclear radiation caused by the earthquake and tsunami at the Fukushima nuclear power plant in Japan, so hearing this term will inevitably lead to a tense mentality. In fact, modern life makes us surrounded by various radio waves. According to the frequency, from low to high, it can be divided into: power frequency; industrial intermediate frequency (including frequency conversion motor frequency band); working band of electronic control device for lighting; radio broadcasting Long wave band, medium wave band, short wave band; frequency band and TV band; mobile communication band; followed by infrared band; visible light band; ultraviolet band and higher frequency x-ray and gamma ray.
2. The difference between electromagnetic wave and ion beam
The most essential difference between electromagnetic waves and ionizing rays is that electromagnetic waves only transfer energy, but the energy transfer process does not cause material transfer. Ion ray not only transfers energy, but also transfers matter during the energy transfer process. The permanent damage caused by radioactive substances entering the human body is fatal.
3, the characteristics of the human body
We know that when the sky produces lightning, it emits a strong broad-spectrum radio wave around it, so all creatures on Earth are regularly exposed to broad-spectrum radio waves before humans produce electricity. Radio wave radiation is accompanied by the evolutionary process of human beings for millions of years, thus creating the characteristics that human beings are suitable for living on the earth: that is, the human body contains more than 70% of water; 95% of non-metals; less than one ten thousandth of magnetically conductive materials, so The human body has a skin-collecting effect on the induced current generated by the radio wave radiation in the electric field, and the magnetic field is basically penetrating and unimpeded. The electromagnetic compatibility limit for the human body mainly considers the electric field effect with the largest weight.
2. International limits on radio emissions in the work area and public living areas
Excessively high and too low levels of environmental electromagnetic waves are not good for modern people. Therefore, the international standard for electromagnetic compatibility of human bodies is established without sacrificing human self-balance.
1. Safety magnitude of alternating power electric field and microwave radiation field
After nearly a hundred years of work and living in various electromagnetic fields, the limits of the safety level of the workers in the alternating power field are shown in Table 1. The limits of the safety level in the microwave radiation field are shown in the table. 2.
It can be seen from Table 1 that for ordinary natural persons, the time in the alternating power electric field is >8h per day, and the safety level that does not destroy the static balance is 600V/m.
For ordinary natural persons, the safety magnitude of the microwave radiation field should consider not only the electric field strength (V/m), but also the energy of the microwave radiation field (mW/cm2). When the time of exposure to the microwave radiation field is ≤ 0.2 per day, The safety level that does not destroy the static balance is not more than 40 V/m, and the energy of the radiation field is not more than 1 mW/cm 2 . It can be seen that the microwave radiation field is far more harmful to the human body than the radio wave radiation field with the frequency of kHz.
2. Radiation limits and analysis of electromagnetic fields by international standards
The radiation limit of the international standard for electromagnetic fields is shown in Figure 1. The relevant description of the figure is as follows:
(1) After nearly a hundred years of work and living in a variety of electromagnetic fields, the limits of Figure 1 were obtained. The BT curve in the figure is the limit for the magnetic field; the E(kV/m) curve is the limit for the electric field; and the S (mW/cm2) curve is the limit for the microwave field. These three quantities of dashed lines are the limits of non-continuous exposure to electromagnetic radiation, and the solid lines of these three quantities are the limits of continuous exposure to electromagnetic radiation. The limits of Tables 1 and 2 are based on Figure 1. of.
(2) The energy of each frequency band of radio waves generated by lightning is mainly concentrated in the 300 Hz to 100 kHz band. The evolution process of humans for millions of years has been most suitable for this radio wave band, so the limits obtained by experiments in the figure are also Correspondingly, it is also awkward in this frequency range.
(3) The blue line is the working frequency region of the current energy-saving lamps and electronic ballasts, and is also the main energy segment of each frequency band of radio waves generated by lightning, so the limit value is relatively wide. For this frequency segment, according to Figure 1, it can be concluded that for the public living area, the magnetic field limit of >8h per day without destroying the static balance is about 10μT, and the electric field is about 300V/m, which is obviously lower than the table. 1 Staff limit.
(4) For the above reasons, in 1991, the US ANSI C95.1 standard and the EU standard both significantly increased the electromagnetic radiation, which was more than 10 times wider. The author once said in the article "Opinions on the topic of "energy radiation from large energy-saving lamps" recently that "GB8702-88 is outdated" (the standard electric field limit is ≤30V/m) is mainly based on this fact.