Key points for testing in different shielded rooms

Full electromagnetic wave anechoic chamber, semi-electromagnetic wave anechoic chamber, and open field. The radiation source experiments carried out in the three detection sites here generally can be felt to be consistent with the propagation regularity of electromagnetic waves in free space. The fully electromagnetic anechoic chamber reduces the impact of external electromagnetic signals on the detection signal. In addition, due to the reflection from walls and ceilings, the harm of multipath effects on detection results can be reduced, making it suitable for transportation, sensitivity and winding tests. In specific applications, if the shielding efficiency of the shielding body can reach 80dB~140dB, then the entire electromagnetic wave anechoic chamber can simulate free space according to the influence of the external natural environment. The reflective surfaces of the road, ceiling and walls of the fully electromagnetic anechoic chamber are smaller than the other two detection points, so they are less affected by the external natural environment and are not affected by the external temperature. Its disadvantages are limited by cost and limited space in the test chamber. The semi-electromagnetic anechoic chamber is similar to the full electromagnetic anechoic chamber. It is also a hexagonal box with a shielding design and is covered with electromagnetic wave absorbing materials inside. The difference is that the semi-electromagnetic anechoic chamber uses conductive wooden floors and is not covered with absorbing materials. Semi-anechoic chamber simulation simulates an ideal wide field situation, that is, the field has an infinite good conductive ground plane. In a semi-anechoic chamber, since the road surface is not covered with absorbing material, a reflective path will occur, and the signal received by the receiving antenna will be the sum of the illumination path and reflective path signals.
An open field is an elliptical or annular experimental site that is flat, broad, has uniform conductivity, and is free of all reflective surfaces. An ideal square road surface has excellent conductivity and an infinite total area. It can accept data signals from wireless antennas between 30MHz and 1000MHz. is the total number of illumination path and reflection path signals. However, in actual applications, although good ground conductivity can be obtained, the area of the wide field is indeed limited, which may cause a phase angle between the transmitting antenna and the receiving antenna. In transmission detection, the application of wide field is the same as that of semi-anechoic chamber. Each electromagnetic compatibility test report stipulates a special testing site, in which the requirements for radiation source emission and radiation source immunity testing are more stringent.
Because the transmission and reception of high-frequency electromagnetic fields of 80 to 1000 MHz is completely based on the theory of superposition of indoor space illumination waves and road reflection waves at the receiving point. If the location is not ideal, a large detection difference will inevitably occur. The broad experimental site is an important electromagnetic compatibility testing site. However, because the construction cost of the spacious experimental field is high and it avoids urban areas, it is troublesome to use; or it is built in urban areas, and the decibel pulse signal is large and affects the EMC test. Therefore, indoor shielded rooms are often used instead. However, the shielded room is a closed body of metal material, and there are many series resonances. When the radiation source frequency of the mechanical equipment under test and the encouragement method promote the series resonance of the shielded room, the data error reaches 20~30dB, so the walls around the shielded room must be installed. Install absorbing materials on the surface, walls and top to greatly weaken the reflective surface, that is, when electromagnetic waves propagate, only straight waves and surface waves are reflected from the road surface. In addition, its structural specifications are based on regulations to simulate outdoor wide-field detection. This is an electromagnetic shielding and absorbing chamber, also known as an electromagnetic shielding and absorbing chamber, which has become a widely used electromagnetic absorbing test site.