Shielding rooms have been used in many fields in China. Many people will wonder what the role of electromagnetic shielding rooms is. In fact, shielding rooms are specially used to attenuate and isolate the building space from internal or external electric and magnetic energy. In order to isolate the external electromagnetic interference, theoretically speaking, EMC technology has two basic rules for absorbing materials: one is to completely absorb, and the other is to make the absorption band as wide as possible. So what absorbing materials have been studied or used in shielding rooms at home and abroad? Let's take a look.
1. Ferrite series absorbing materials (nickel-zinc ferrite, manganese-zinc ferrite, barium ferrite, etc.): due to the resonance absorption of ferromagnetic materials and the dispersion effect of magnetic permeability, ferrite materials have The advantages of strong absorption and wide frequency bandwidth are widely used in various stealth technical fields.
2. Micro-powder absorbing materials: Micro-powder materials (especially nano absorbing materials) have received attention from all aspects due to their peculiar physical and chemical properties. The reflection of electromagnetic waves is small and the absorption is high. It is a new material worth paying attention to. The surface atoms in the particles of the micro-powder material account for a large proportion of the entire particle atoms. Due to the large number of dangling bonds and empty bonds, the activity of the surface atoms is greatly increased. When electromagnetic waves are incident on such particles, the movement of molecules and electrons intensifies, the conversion of electromagnetic energy into heat energy is highly efficient, and the electromagnetic loss is large. Its transmission and absorption performance depends on the size of the particle size. This feature can be used to achieve interlayer turn matching The purpose of widening the frequency band.
3. Polycrystalline ferromagnetic metal fiber: Polycrystalline ferromagnetic metal fiber has unique shape characteristics and composite loss mechanism (magnetic loss and dielectric loss), light weight (density <2kg/m2), frequency bandwidth (4～18GHz) ) And the advantages of good oblique incidence performance, and the electromagnetic parameters of the absorber can be adjusted by adjusting the length, diameter and arrangement of the fiber.
4. Hickoff's base retinoid: black like graphite, absorbing performance is better than other materials, and the weight is only 1/10 of the iron ball absorbing material. The absorbing frequency bandwidth of this material is effective from long wave to 8mm wave band. It converts all electromagnetic wave energy into heat energy through ion displacement method, but the temperature rise of the material itself is not obvious.
5. Dielectric ceramic absorbing materials: PZT (lead zirconate titanate), BaTiO3 and other dielectric materials also have good absorbing effects, but the absorption bandwidth is small.
6. Conductive polymer material: Compared with other absorbing materials, it has the characteristics of low density (only 1/5 of ferrite). The absorbing performance can be controlled by adjusting the conductivity by doping. Foreign reports have- Bandwidths of 10dB and 12GHz.
7. Chiral absorbing material: Compared with ordinary materials, it has chiral parameters. The electromagnetic wave propagating in it can only be left-handed or right-handed circularly polarized waves. Its advantage is that the impedance can be adjusted by adjusting the chiral parameters. Matching is much easier than adjusting μ and ε; in addition, it has low frequency sensitivity and is easy to achieve broadband absorption.