1. Spinel type ferrite absorbing material
The development of spinel-type ferrite absorbents at home and abroad has a long history. NiZn ferrite was prepared. In the frequency band of 200MHz~1GHz, >10, p>30, c in 10~20, c" is very small, and the absorption rate R<-10dB when the coating thickness is 4mm, Cho et al. studied NiZnco spinel ferrite, found that with the increase of Cσ2- content, the resonance frequency moves to the high end. Domestic research on spinel ferrite also has finalized products, using citric acid and metal salts as raw materials to use organic The gel-thermal analysis method successfully prepared Mn.2Zno.8Fe2Ce2O4 (x=0~0.04) series ferrite fibers. Because the rare earth ion Ce3+ has a large ion radius, when Ce3+ enters the MnZn ferrite spinel lattice Later, the lattice constant and lattice size increased slightly with the increase of the doping amount, but the fiber structure did not change significantly. In addition, Ce3+ doping has an effect on the AO-B super exchange effect and anion distribution in MnZn ferrite. And the coupling between the electron spins has also produced a certain degree of influence, which causes the saturation magnetization of MnZn ferrite to increase, the coercive force decreases, and the soft magnetic performance is improved. Because of the spinel ferrite magnet The crystal anisotropy field (HA) is very small, which limits its application frequency. Its magnetic permeability and absorption characteristics in the microwave frequency range (greater than 108 Hz) are generally inferior to hexagonal ferrite, which significantly improves the spinel ferrite The microwave permeability of the body is limited both in theory and in practice.
2. Nano-ferrite absorbing materials
Compared with conventional materials, the proportion of interface components of nanomaterials is large, the proportion of atoms on the surface of nanoparticles is high, and there are many unsaturated bonds and dangling bonds. The existence of a large number of dangling bonds polarizes the interface and broadens the absorption band; nanomaterials quantum size effect The electron energy level is split, and the split energy level spacing is in the microwave energy range of 10-2eV), creating a new absorption channel for nanomaterials; the movement of atoms and electrons in nanomaterials intensified under the irradiation of the microwave field, Increase the efficiency of converting electromagnetic energy into thermal energy, thereby improving the absorption performance of electromagnetic waves. Therefore, nanomaterials have excellent absorbing properties.
The wave absorption effect of nano barium ferrite is better than that of conventional size materials. The maximum reflection attenuation of the material with a particle size of 76m can reach 28dB, and the absorption bandwidth greater than 10dB can reach 6GHz, which is in the entire frequency range of 6.8~18GHz. , The absorption is greater than 5dB. The chemical co-precipitation method and the mechanical ball milling method are combined to prepare a nano W-type barium ferrite with a composition of Ba(Zna5Co3)2Fe16O2. The sample powder with a mass fraction of 75% and epoxy resin are mixed and pressed into an outer diameter of 7mm. , Rings with an inner diameter of 3mm and a thickness of 3~4mm are tested for the absorption performance. The research results show that the absorption peak of the sample has a tendency to move to high frequency as the thickness decreases, so that you can change the coating thickness by changing the thickness of the coating. Thereby changing the frequency of application of the absorbent. A nano W-type barium ferrite sample with a composition of Ba(Zn0.7Coo.3)2Fe16O2 was synthesized by the sol-gel method. XRD test showed that the average particle size of the sample is about 65mm, which is 5μm compared to the average particle size prepared by the conventional method. For the micron-level samples, its absorbing ability is significantly higher than the latter, and the loss is greater than 10dB with a frequency bandwidth of 5GHz, while the latter is only 3.5GHz; the peak loss value reaches 28.5dB.
The nano-Ni0.5Zno.sCe Fe2-xO4 (x=0,0.005,0.01,0.015) ferrite absorbing material was prepared by chemical co-precipitation method, and the sample was tested in the 8.212.5GHz range with the AV3618 microwave vector network analyzer The experimental results show that the content of rare earth elements affects the absorbing performance of the material. When x=0.01, the absorbing performance of nano-Nio.sZno.s Cer Fe2-xO4 ferrite is the best. For Ni.sZno.sCe.oFe1.99O4 ferrite absorbing material, when the coating thickness is 1mm, there are three absorption peaks in the test frequency band, the first absorption peak is at 8.8GHz, and its absorption peak is 15.4dB. The second absorption peak is located at 9.5GHz, its absorption peak is 14.8dB, and the third absorption peak is located at 1.6GH, its absorption peak is 13dB, and the bandwidth above 10dB reaches 3.8GHz.