How to layout the absorbing materials in the anechoic chamber

For radiation testing, there are three types of testing sites: full anechoic chamber, semi anechoic chamber, and open field. The radiation tests conducted in these three testing sites can generally be considered to comply with the propagation law of electromagnetic waves in free space. The full anechoic chamber is a six sided box designed with shielding, covering the floor, walls, and ceiling insideElectromagnetic wave absorbing materialsThe absorbing material is generally a cone made of polyurethane foam material, which can effectively absorb the incident electromagnetic wave energy and make its scattering attenuate significantly. However, because the low frequency performance of the cone absorbing material is poor, it is usually used to use both ferrite andCone shaped absorbing materialTo improve the low-frequency performance of the darkroom.

The full anechoic chamber reduces the interference of external electromagnetic wave signals on test signals, and electromagnetic wave absorbing materials can reduce the multipath effect caused by reflections from walls and ceilings on test results, making it suitable for emission, sensitivity, and anti-interference experiments. It can ignore the interference of the external environment and simulate free space in a fully anechoic chamber. Compared with the other two testing sites, the ground, ceiling, and walls of the full anechoic chamber have the smallest reflections, are least affected by external environmental interference, and are not affected by external weather. Its disadvantage is that it is constrained by cost and has limited testing space.

A semi anechoic chamber is similar to a fully anechoic chamber in that it is a shielded hexagonal box covered with electromagnetic absorbing material inside. The difference is that a semi anechoic chamber uses a conductive floor and is not covered with absorbing material. A semi anechoic chamber simulates an ideal open field situation, where the site has an infinitely large, well conductive ground plane. In a semi anechoic chamber, due to the lack of absorbing materials covering the ground, a reflection path will be generated, and the signal received by the receiving antenna will be the sum of the direct and reflected path signals.

In order to balance important functions such as EMC testing research of automotive components, performance research of half wave and full wave anechoic chambers, and EMC testing research of engineering, medical, and information technology products, a ten meter half wave anechoic chamber and a three meter half/full wave anechoic chamber were ultimately adopted. The ten meter half wave anechoic chamber (later referred to as the large anechoic chamber) is mainly used for EMI and EMS testing of vehicles and large EUTs, while the three meter half/full wave anechoic chamber (later referred to as the small anechoic chamber) is mainly used for EMI and EMS testing of components and other products.

Used in large and small darkroomsAbsorbing materialCompliant with the flame retardant and fire prevention standards of the United States and Europe, the FS wedge material treated with the new process can increase weight by no more than 5% in 240 hours under a relative humidity of 95%, and the physical and electrical properties of the absorbing material remain unchanged. The layout of absorbing materials in the large and small darkrooms is shown in Table 2 and Table 3, respectively. YB-18 ferrite is used in the large darkroom, with YB-17 absorbing spikes (1m high). YB-13 ferrite and YB-15 are laid on the ground, and YB-12 is laid locally for testing above 1GHz for EMS testing to meet the requirements of field uniformity; The small darkroom adopts the latest design of advanced institute technology composite absorbing materials, with a compact appearance. Cover the four walls and ceilings of the darkroom, provide a corresponding amount of reflective flooring on the floor, and provide a 50kg load-bearing absorbing material channel YB-25 at the location where walking is required. The tip of YB-26 absorbing material is covered with white foam reflector.

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