Understanding the two standards of electromagnetic radiation
1. Power density standard
Power density refers to the radiation power received per unit area, which measures the signal strength and can be represented by electric field strength and magnetic field strength, but the more commonly used is power density. The following figure shows the regulations on public exposure limits in China's current "Regulations on Electromagnetic Radiation Protection" (GB8702-88). The first two rows in the figure belong to the medium and short wave frequency bands, not the mobile communication frequency band. Among them, 3MHz-30MHz is the short wave band used by the military and has little to do with the public, so there is no need to worry. The higher the frequency of electromagnetic waves in the range of 30MHz to 30000MHz, the poorer their ability to penetrate the human body. Therefore, from the perspective of their impact on the human body, the higher the frequency, the greater the allowed power density, from 0.4W/m2 at 30MHz to 2W/m2 at 30000MHz.
The peak power of mobile phones is 2W, and the Institute of Electrical and Electronics Engineers (IEEE) does not consider safety issues for transmission power below 7W. However, the National Committee on Radiation Protection (NCRP) in the United States advocates stricter standards. The Federal Communications Commission (FCC) in the United States sets a radiation limit of 6W/m2 for the 900MHz frequency band used by 2G mobile phones, which is 15 times looser than China's 0.4W/m2.
2. Specific absorption rate standard
The definition of Specific Absorption Rate (SAR) is: the differential value of the energy absorbed by a mass element within a volume element of a given density over time. It actually refers to the electromagnetic energy absorbed per unit of time and per unit of biological mass, measured in W/kg.
Compared to the power density standard introduced earlier, this standard takes into account human conditions more and should be a more worthy reference standard, but it is difficult to operate. The verification of power density standards is very simple, which can be measured with a field strength meter or spectrum analyzer. However, the verification of absorption rate standards requires the cooperation of a human body model, and the subsequent data algorithms are also very complex.
The American standard established by the National Committee on Radiation Protection and Measurement (NCRP) and the Institute of Electrical and Electronics Engineers (IEEE) is SAR ≤ 1.6W/kg, while the European standard established by the International Commission on Non Ionizing Radiation Protection (ICNIRP) is SAR ≤ 2.0W/kg, which is recommended by the World Health Organization (WHO). The main content of China's "Local Exposure Limits for Electromagnetic Radiation from Mobile Phones" (GB21288-2007) is only one page, which actually states one sentence: China follows the European standard of 2.0W/kg recommended by the World Health Organization.
