Overall shielding against electromagnetic radiation within the immediate area
The phenomenon of electromagnetic radiation refers to the harm caused to the human body and interference with the normal operation of electronic devices by the electromagnetic radiation generated by high-power transmitting equipment. Natural electromagnetic radiation comes from Earth's thermal radiation, solar thermal radiation, cosmic rays, and static electricity; Artificial electromagnetic radiation has a wide range of sources, including the operation of high-voltage lines, substations, radio stations, electronic instruments, medical equipment, laser photography equipment, and office automation equipment, as well as the use of household appliances such as microwave ovens, televisions, mobile phones, air conditioners, electric blankets, and radios.
The electromagnetic radiation field is generally divided into near-field and far-field. The region centered around the field source within one wavelength range is commonly referred to as the near-field; On the contrary, the region outside of one wavelength range is usually referred to as the far-field. The two types of fields have different characteristics: in the near-field, there is no definite proportional relationship between the electric field strength and the magnetic field strength. In general, for field sources with high voltage and low current, such as transmitting antennas, feeders, etc., the electric field is much stronger than the magnetic field; For low voltage and high current field sources, such as certain induction heating devices, the magnetic field is much larger than the electric field. In the far-field, all electromagnetic energy is radiated and propagated in the form of electromagnetic waves, and the attenuation of radiation intensity in this field is much slower than that in the induction field. In the far-field, the electric and magnetic field strengths have the following relationship: E=377H, the direction of the electric and magnetic fields is perpendicular to each other, and both are perpendicular to the direction of electromagnetic wave propagation. The far-field is a weak field, and its electromagnetic field strength is relatively small.
The electromagnetic field intensity in the near-field is much greater than that in the far-field, and electromagnetic radiation mainly affects and damages the human body in the near-field. This article intends to provide some ideas and practices for the overall shielding design of electromagnetic radiation protection within the vicinity of the site.
