Choosing different absorbing materials, the shielding room will have different shielding performance. Nowadays, many types of absorbing materials have been developed. The following will mainly talk about what kind of absorbing material such as ferrite is.
Electromagnetic wave attenuation classification standard
1. The basic physical principle of the absorbing material is that the material can effectively absorb the incident electromagnetic wave and convert the electromagnetic wave energy into heat or other forms of energy for loss. The material should have two characteristics, namely, wave impedance matching characteristics and attenuation characteristics, wave impedance matching characteristics, that is, creating special boundary conditions to minimize the reflection coefficient of incident electromagnetic waves on the surface of the material medium, so as to enter the medium from the surface as much as possible.
2. Attenuation characteristics mean that electromagnetic waves entering the material are quickly absorbed due to loss. The magnitude of loss can be characterized by electrical loss factor and magnetic loss factor. To improve the efficiency of the medium's wave absorption, the basic way is to increase the conductivity of the medium, increase the polarization "friction" and the magnetization "friction", and at the same time meet the impedance matching conditions, so that electromagnetic waves do not reflect and enter the medium to be absorbed.
3. For a single-component absorber, impedance matching and strong absorption must be met at the same time, and there are often contradictions. Therefore, it is necessary to multi-element composite materials in order to adjust the electromagnetic parameters to improve the absorption loss ability under matching conditions as much as possible. .
What is ferrite?
1. Ferrite is composed of several kinds of oxides with trivalent iron ions as the main positive ion components, and exhibits ferrimagnetic or antiferromagnetic materials.
2. Ferrite is a metal oxide with ferromagnetism. In terms of electrical properties, the resistivity of ferrite is much larger than that of metal and alloy magnetic materials, and it also has higher dielectric properties. The magnetic properties of ferrite also show high permeability at high frequencies. Therefore, ferrite has become a non-metallic magnetic material with a wide range of applications in the field of high frequency and weak current. Because the magnetic energy stored in the unit volume of ferrite is low, the saturation magnetization is also low (usually only 1/3 to 1/5 of pure iron), which limits its use in low-frequency strong electric and high magnetic energy density requirements. Applications in high-power fields.
3. Ferrite magnetic materials can be represented by the chemical formula MFe2O4. In the formula, M represents divalent metal ions such as manganese, nickel, zinc, and copper. Ferrite magnetism is manufactured by sintering a mixture of these metal compounds.
4. The main feature of ferrite magnetism is that the resistivity is much greater than that of metal magnetic materials, which suppresses the generation of eddy currents and makes ferrite magnetism suitable for high-frequency applications.
5. The wave-absorbing performance of ferrite comes from its both ferrimagnetic and dielectric properties. Its relative permeability and relative conductivity are both in plural form, which can produce both dielectric loss and magnetically induced loss. , So the ferrite absorbing material has good microwave performance.
Selection process of ferrite absorbing material
1. First, according to the predetermined proportion of the formula, mix the high-purity, powdery oxides (such as Fe2O4, Mn3O4, ZnO, NiO, etc.) uniformly, and then calcinate, crush, granulate and press to form at high temperature (1000～ Sintering at 1400°C). The sintered ferrite products are processed to obtain the finished size.
2. The above-mentioned processes are strictly controlled to ensure that all the characteristics of the product meet the specified indicators. Different ferrite materials should be selected for different purposes. There is a series of linear materials with magnetic permeability suitable for low loss and good high frequency characteristics. According to different applicable frequency ranges, it can be divided into: middle and low frequency band (20～150kHz), middle and high frequency band (100～500kHz), ultra-high frequency band (500-1MHz).
3. When used as absorbing materials, ferrite mainly has two forms: one is compounded with adhesive to make composite materials, which can be products such as coatings and rubber. These materials have low permeability and require thicker materials to absorb microwaves well. The other is sintered ferrite. Because the internal structure of sintered ferrite is relatively continuous, the material can obtain higher magnetic permeability. Its disadvantage is that the material is heavier and fragile, and the high temperature resistance is weak.
The various properties of ferrite determine its absorbing performance, and more research is now being carried out to find better absorbing materials.