Radio wave absorbing materials can be divided into four types of absorption, interference, resonance, and plasma. The absorbing materials are mainly composed of dielectric materials (such as barium titanate porcelain, ferroelectric ceramics, etc.), magnetic dielectric materials (such as ferrite, carbonyl iron, etc.) 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. Utilize 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 changes uniformly or gradiently with the thickness of the material. Etc.) and a conductive material layer, using the anti-phase interference effect of electromagnetic waves, so that the incident wave and the electromagnetic wave energy reflected from different layers interfere with each other and cancel in order to obtain a good cancellation effect, so that the reflected echo of the target is close to zero. The thickness of the interferometric material should be an odd multiple of a quarter wavelength of the radar. The absorption frequency band of the interference type material is narrow and the cancellation effect is greatly related to the incident angle of the electromagnetic wave, but the material thickness can be made very thin when used at high frequencies. The resonant type material is made of multiple absorption units made of non-conductive dielectric materials. These units have a certain size and electromagnetic characteristics, and can produce resonance absorption for incident electromagnetic waves of corresponding wavelengths. Appropriate combination of resonant 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, which is 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 application LCD screen medical equipment notebook computer, game console communication equipment, wireless identification system digital camera, digital camera camera mobile phone , Smartphones, PDAs, PMPs, GPS navigators, electromagnetic wave absorbing sheet features Thin strip shape, light weight and flexibility, can be bent without breaking, can be processed into various shapes, to facilitate the adhesion of the product on the multi-layer high magnetic permeability and high loss Metal composite with high absorbing efficiency 4. Effectively convert electromagnetic wave energy into heat energy. There is no general conductive material to block the electric wave, and the phenomenon of reflection, diffraction and crawling caused by metal materials can absorb electromagnetic waves. Of course, the reflection of electromagnetic waves is also very high. Metal materials After absorbing 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, which convert the energy of electromagnetic fields (light energy) into electrical energy for human use; various photodetectors It is also made of semiconductor materials and is used to detect electromagnetic waves in different bands. For example, night vision devices are realized by using materials that absorb electromagnetic waves in the infrared band.
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, transition, and rebound, and then release it in another form, so that it 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 means of absorption and isolation, that is, shielding is the main method. The energy of electromagnetic waves is not large and can generally be absorbed by metals. Even if the energy is large, it can be in the periodic table of elements. Heavy metal elements have the largest energy loss to electromagnetic waves. This is why X-ray diffraction and nuclear magnetic resonance diffraction are generally used in the medical research field. The reason is because of the 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 case of a computer is like this. The package acts as an isolation, but due to energy excitation, it 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.