Absorbing materials can be divided into four types of absorption type, interference type, resonance type and plasma type. They are mainly composed of dielectric materials (such as barium titanate porcelain, ferroelectric ceramics, etc.), magnetic dielectric materials (such as ferrite, carbonyl Iron, etc.), resistance materials (such as carbon black, silicon carbide, etc.) or their composite materials are made by adding appropriate binders. Among them, ferrite magnetic media materials are most used.
Using the dielectric loss, hysteresis loss and resistance loss of these materials in the alternating electromagnetic field, the electromagnetic wave energy incident on the inside is converted into heat energy and absorbed. The advantage of absorbing materials is that the absorption band is wider, but the thickness is related to the lowest frequency of the incident wave. The absorption of low-frequency electromagnetic waves is generally achieved by increasing the thickness of the material, and the dielectric constant or permeability is often changed or uniformly changed with the thickness of the material. The gradient-changing multilayer structure interference material is composed of intersecting dielectric layers (such as plastic, rubber, etc.) and conductive material layers. The anti-phase interference effect of electromagnetic waves is used to make the incident wave and the electromagnetic wave energy reflected from different layers mutually interact. Interference and cancellation In order to obtain a good cancellation effect, the reflection echo of the target should be close to zero, and the thickness of the interferometric material should be an odd multiple of a quarter wavelength of the radar.
The absorption frequency band of interference-type absorbing materials is narrow and the cancellation effect is greatly related to the incident angle of electromagnetic waves, but the material thickness can be made very thin when used at high frequencies. The resonant-type materials are made of non-conductive dielectric materials. The absorption unit constitutes these units with a certain size and electromagnetic characteristics, which can produce resonance absorption for incident electromagnetic waves of corresponding wavelengths. Appropriate combination of resonance units of various sizes can obtain broadband absorption characteristics. However, this kind of material is difficult to manufacture, so it is rarely used.
Plasma-type materials are composed of radioactive isotopes (such as strontium 90, polonium 210, curium 242, etc.) and a binder coated on the target surface to ionize the local space near the target surface to form a plasma zone that absorbs electromagnetic waves. Radar coating has the advantages of being thin and light, not affecting aircraft performance, good absorption performance, absorption frequency bandwidth, etc. Electromagnetic wave absorption sheet applications LCD screen medical equipment notebook computers, game console communication equipment, wireless identification system digital cameras, digital cameras, cameras, mobile phones , Smartphones, PDAs, PMPs, GPS navigators electromagnetic wave absorption sheet features thin strip shape, light weight and flexibility, bendable without breaking, can be processed into various shapes to facilitate the adhesion of products, and effectively convert electromagnetic wave energy into heat.
Metal absorbing materials can absorb electromagnetic waves, and of course their reflection of electromagnetic waves is also very high. After metal materials absorb electromagnetic waves, the energy of the electromagnetic field is mainly converted into heat energy and semiconductor materials can also absorb electromagnetic waves of specific wavelengths, such as solar cells. The energy of the electromagnetic field (light energy) is converted into electrical energy for people to use; various photodetectors are also made of semiconductor materials, which are used to detect electromagnetic waves in different bands. For example, night vision devices use materials that absorb electromagnetic waves in the infrared band. Realized, electromagnetic waves are too extensive. Generally speaking, molecules and atoms have a certain absorption capacity. When high-frequency electromagnetic wave energy radiates to them, they absorb energy, jump, and rebound, and then release it in another form. This is absorbed. In other words, our common sodium lamps (commonly used in street lamps) and other gas-emitting lamps use this principle. However, the current method of isolating high-frequency electromagnetic fields is generally by absorption and isolation, which is Shielding is the main thing. If the electromagnetic wave energy is not large, it can generally be absorbed by the metal, even if the energy is large, it is also possible. In the periodic table, heavy metal elements have the largest energy loss to electromagnetic waves, which is why X-ray diffraction and nuclear magnetic resonance in the medical research field Diffraction is generally due to heavy lead plates. For ordinary low-power radiation, it is generally only necessary to wrap it with metal and then ground it. For example, the computer chassis is such a principle that the package plays a role of isolation, but Due to the energy excitation, he will also release the absorbed energy in other forms of energy. If it is grounded, it will be introduced into the earth and will be naturally lost.