the difference between a shielded room and a dark room

The shielding room is just a large iron box that blocks the radio signals inside and outside. Simply put, the inside cannot go out and the outside cannot come in, but the electromagnetic waves inside will reflect and stack on the inner wall.

An anechoic chamber is based on a shielding chamber, with absorbing materials laid on the inner wall to simulate the effect of an open field. The anechoic chamber is much more expensive than a shielding chamber, but it is more expensive to stick these materials inside the anechoic chamber. The electromagnetic waves inside will be absorbed when emitted to the inner wall, and there will be basically no mixed wave effect of reflection and superposition. Suitable for testing the radiation emission interference of samples. Anechoic chambers are generally divided into full anechoic chambers and semi anechoic chambers.

Tests that do not have high requirements for the experimental environment, such as conducted disturbances, static electricity tests, surge tests, lightning tests, etc., are all conducted through power lines, so they only need to be conducted in a shielded room; For spatial radiation, spatial disturbance transmitted through space, or anti-interference, there are special requirements for space, so it needs to be carried out in a dark room to simulate the space of an open field.

Radiation tests conducted in full anechoic chamber, semi anechoic chamber, and open field can generally be considered to conform to the propagation laws of electromagnetic waves in free space.

The full anechoic chamber reduces the interference of external electromagnetic wave signals on the test signal, and electromagnetic wave absorbing materials can reduce the multipath effect caused by the reflection of walls and ceilings on the test results. It is suitable for emission, sensitivity, and immunity experiments. In practical use, if the shielding effectiveness of the shielding body can reach 80dB~140dB, then the interference to the external environment can be ignored. In a fully anechoic chamber, the situation in free space can be simulated. Compared with the other two testing sites, the floor, ceiling, and wall of the full anechoic chamber have the smallest reflection, are least affected by external environmental interference, and are not affected by external weather. Its disadvantage lies in cost constraints and limited testing space.