Microwave Absorbing Mechanism Of Percolative BT-NZF Composite Powder

Microwave absorbing material is initially exploited as a purpose for detection avoidance such as camouflage in military. With the advent of information age, electromagnetic wave pollution poses a threat to human and our environment. Also, electromagnetic interference (EMI) problems cause severe interruption due to the growth in the electronic devices. To overcome electromagnetic wave pollution and EMI, microwave absorbing materials with the capability of absorbing unwanted electromagnetic signals are extensively demanding.The researchers all around world have focused on obtaining novel material with excellent microwave absorbing properties such as high absorption and broad bandwidth. Ferroelectirc/ferromagnetic composite material is a promising material due to both dielectric property and magnetic property.This dissertation reviewed the development and application of the microwave absorbing material, and introduced the goodness of composite absorbing material. Besides, the various methods of preparing composite material were summarized; the sol-gel technology route was introduced in details. In this paper, BaTi03-Ni_0.5Zn_0.5Fe₂O₄ percolative composite powder was prepared by sol-gel method in situ. The pure two-phase composite powde was got by changing the heat treatment temperature and the ratio of two means. XRD was adopted to study the structure and the phases of the composite powder. Transmission electron microscopy (TEM) was adopted to study the interface state of two-phase composite powder. The dielectric and magnetic properties and microwave absorbing properties were measured by vector network analyzer. The particle size of composite powder was tested by laser particle size analyzer. Specific research content and conclusions are listed as follows:In this paper, percolative BaTi03-Nio.5Zn_0.5Fe₂O₄ composite powder was prepared by the sol-gel in situ method with sintered at different temperatures, the results show that composite system gradually began to form by BT and NZF when the temperature rises to 950℃, and the two-phase composite powder ratio have a certain influence on the frequency range of microwave absorbing of composite powder. BT/NZF-2/8 has the best microwave absorbing properties,on the one hand, BT phase can partially compensate for the gap between dielectric and magnetic properties of NZF phase; on the other hand, according to the characteristics of percolation theory, the complex has obvious percolation system architecture, and the percolation threshold is 80%, and the real and imaginary parts of dielectric constant to obtain the maximum value at the percolation threshold of two-phase composite system, at which point the NZF content of system, with a larger permeability values of the real and imaginary parts. which makes permittivity and permeability achieve the best impedance matching degree.The absorbing peak of composite powder can access to-35dB and absorbing bandwidth can reach 7GHz as getting the best impedance matiching,which is 2 times higher than the mixied powder.We milled the percolative composite powder with perfect matching factors to increase the contact area between particles, and got the medium with stronger attenuation ability. Attenuation constant can reach 800GdB as the matching factors nearly 1 and the value of reflection loss also reach-50dB. This value enhanced 50% compared to un-milled composite powder and the absorbing band-with always was not reduced.In addition, the thickness of the composite powder was investigated with taking into account the application characteristics of absorbing materials. The results show that: Powder particle size increases with milling time, also there is a limit for particle size. The peak value of absorbing ability of composite powder particle size decreases with increasing particle size.However, the particle size has little effect on the bandwidth absorbing powder, which keeps 6-7GHz; The loss peak frequency moves gradually to low with the increased media thickness from 2mm to 3mm. This composite powder has best microwave absorbing ability when the thickness is 2mm.