Electromagnetic wave absorber is an effective means to improve the survivability and penetration capability of weapon systems, and thus has become one of the key high-tech researches in the world today. Both theory and experiments have confirmed that the electromagnetic properties of the material are improved after anisotropy, and the wave-absorbing performance is improved; at the same time, the electromagnetic parameters can be adjusted by changing the morphology size, which is more conducive to the realization of impedance matching; in addition, the sheet-like shape of the material Therefore, the research on electromagnetic wave absorber materials with anisotropy is of great significance to the research and development of a new generation of thin, light, wide and strong stealth materials.
For the traditional spherical electromagnetic wave absorber, when the initial permeability is increased, the natural resonant frequency decreases. On the contrary, when the natural resonant frequency increases, the initial magnetic permeability decreases. It is difficult to increase the magnetic permeability and the resonant frequency of the material at the same time. To further improve the magnetic properties of magnetic materials at high frequencies, this limitation must be overcome, and anisotropy is an effective way. Studies have shown that anisotropic films, fibers, and sheet-like magnetic materials can simultaneously increase the magnetic permeability and resonance frequency, and have excellent high-frequency magnetic properties. It can have a stronger and wider frequency radar loss effect in the field of electromagnetic wave absorber materials.
- Magnetic fiber electromagnetic wave absorber
The strong shape anisotropy of the magnetic fiber absorbing material makes it have a larger magnetic permeability and magnetic loss in the microwave frequency band. The study found that the ferrite fiber with an aspect ratio of 50 is compared with the non-fiber magnetic material with the same content. The permeability is increased by a factor of 50. At the same time, the magnetic fiber absorbent also has large turbine loss, ohmic loss and radiation loss at high frequencies, and is a strong electromagnetic wave absorber material. In addition, this type of absorbent also has the advantages of light weight, low areal density, and wide frequency band, and the electromagnetic parameters of the material can be adjusted by adjusting the length, straightness, and arrangement of the fibers. High absorption is achieved in a very wide frequency band, and the mass is 40% to 60% lighter than that of traditional metal micropowder electromagnetic wave absorber materials. It has a good application prospect in the development of lightweight and high-efficiency stealth materials. Common magnetic fiber absorbing materials include iron fibers, nickel fibers, cobalt fibers and their alloy fibers. Europe has successfully developed a radar stealth coating using polycrystalline iron fiber absorbing materials, which has achieved broadband absorption, and its maximum absorption can reach 34dB. Fiber-based composite materials are one of the hotspots of current research. For example, a magnetic material with Fe-Co alloy clad carbon fiber has a reflection loss of 48.2dB in the 2-18 GHz frequency band.
- Magnetic film electromagnetic wave absorber
With the development of physical vapor deposition and chemical vapor deposition technology, the electromagnetic properties of magnetic thin film electromagnetic wave absorber materials are also continuously improved. The magnetic alloy films and multilayer films with Fe and Co as the main body have high magnetic permeability and magnetic loss at microwave frequencies, which can realize broadband absorption of microwaves. It is reported that the CuO/Co/carbon fiber multilayer film composite material is prepared by thermal oxidation method, and the strongest reflection loss can be increased to 42.7dB, which is an ideal lightweight, strong absorption, broadband microwave absorption material.
- Sheet electromagnetic wave absorber
Research on flake ferromagnetic materials shows that when the flattening ratio is 10-10000, its microwave permeability can be increased by 10-100 times. This is due to the increase in the surface area of the particles caused by the increase in the flatness of the alloy powder and the decrease in the particle size. On the one hand, the polarization of the space charge of the powder and the magnetic moment exchange coupling between adjacent particles are enhanced. On the other hand, the eddy current losses of the powder are reduced, thereby increasing the complex permittivity and complex permeability of the composite components.
What are the three main types of electromagnetic wave absorber principles?
- Absorptive wave absorbing material, which absorbs electromagnetic waves in the material and dissipates it.
- Reflective wave absorbing material shields the electromagnetic wave (radar wave) on the surface of the material, reduces the radar wave reflection cross section, and reflects the radar wave to the non-important area to minimize the radar wave acceptance.
- Interference type absorbing materials, through a certain structure or material design on the surface of the material, the electromagnetic waves exist in the optical path difference to cause mutual interference and cancellation.
Absorbing material is a functional composite material that mainly absorbs electromagnetic waves. It eliminates the back and forth reflection of electromagnetic waves in the shielding cavity, reduces the interference of clutter to its own equipment, and also effectively prevents electromagnetic radiation from harassing and harming surrounding equipment and personnel. An advanced means of eliminating electromagnetic wave pollution. Common thicknesses include: 0.08mm 0.1mm 0.2mm 0.3mm In handheld devices such as NFC payment mobile phones, electronic tags should be integrated or attached to electronic devices to function as a part of the device, often due to limited space, it is inevitable to Attach RFID tags (usually passive) to the surface of conductive objects such as metal or to places where there are metal devices in the vicinity. In this way, the alternating electromagnetic field excited and induced by the tag under the action of the signal from the card reader is easily attenuated by the eddy current of the metal, which greatly weakens the signal strength, resulting in the failure of the reading process. Therefore, in order for the product to be able to better read the card, it is necessary to add absorbing materials to the product.
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