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Microwave Absorbing Mechanism of Percolative BT-NZF Composite Powder

Author: ZhangXuHui
Tutor: DuZuoYi
School: Zhejiang University
Course: Materials Science
Keywords: Sol-gel In situ Ferroelectric - ferromagnetic composite powders Absorbing properties Percolative Particle size Thickness
CLC: TB383.3
Type: Master's thesis
Year: 2011
Downloads: 25
Quote: 0
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Abstract


Absorbing materials was first used in the military field. After entering the information age, the electromagnetic pollution became a huge threat to human, which prompted absorbing materials to occupy an important position in the electronic devices and other civilian areas. Explore the high absorption rate, broad absorption band excellent overall performance absorbing material has become the main goal of the researchers. Ferroelectric ferromagnetic composites along with the magnetic properties of the dielectric properties of ferroelectric phase and ferromagnetic phase, expected to take advantage of the high absorption rate of its preparation, the frequency bandwidth of high-performance absorbers. Comprehensive overview of the research and development status of the absorbing material, and the advantages of the composite absorber. In addition, the paper also summarizes the preparation of the composite absorber, which focuses on the characteristics of the preparation of the sol-gel method. This article using the sol-gel Situ composite prepared the percolative of BaTiO 3 -Ni 0.5 Zn 0.5 Fe 2 O 4 Composite Powder by changing the firing temperature and the proportion of two-phase means a pure two-phase composite powders were prepared, and its structure and crystalline phases formed by XRD studies, scanning electron microscopy observed complex phase morphology of the powder, the interface state transmission electron microscope observation of complex two-phase phase powder using a vector network analyzer on the dielectric properties of the composite materials, magnetic properties, absorbing performance measurement, and also the use of laser the particle size of the composite powder was tested by the particle size analyzer. The specific content and conclusions are as follows fired at different temperatures using the sol-gel in situ composite preparation method percolative of BaTiO 3 -Ni 0.5 Zn 0.5 < / sub> Fe 2 O 4 Composite Powder, results show that the system, when the temperature is raised to 950 ℃, gradually began to take shape by the BT NZF the complex phase of the two-phase system, and the proportion of two-phase composite powder Composite Powder absorbing range to some extent. BT/NZF-2/8, best microwave absorbing properties of the composite powder, on the one hand, BT phase can partially compensate for NZF relative dielectric and magnetic properties, differences, so that the composite powder impedance matching than other proportion Composite Powder closer to 1; to seepage architecture based on the characteristics of the percolation theory, the complex phase system, and the percolation threshold NZF composite powder in a ratio of 80%, near the percolation threshold, the complex phase system in the two-phase interface contact area, so to obtain the maximum value of the real and imaginary parts of the dielectric constant of the complex phase system, the system ferromagnetic phase NZF content, permeability real part and the value of the imaginary part, so that the dielectric constant and the magnetic permeability of the medium to achieve optimum impedance matching. Optimum impedance matching composite powder can obtain better microwave absorbing properties, absorbing peak value of-35dB absorbing bandwidth to reach 7GHz. The RL value than the two-phase simple mixed absorbing materials increased by 40%, the Radar Absorbing bandwidth increased to 2 times. This article makes further increases the contact area between the particles by the seepage type complex with the best impedance matching phase powder milling longer time to achieve a substantial increase in seepage type Composite Powder defects successfully obtained a higher referral electric loss and magnetic loss and stronger attenuation of electromagnetic capability percolative composite powder. Get impedance matching is close to 1, the decay constant can be achieved 800GdB, the RL value is the maximum capacity of close to-50dB, the percolative composite powder without milling compared to about 50%, while the microwave absorbing bandwidth does not reduce. Taking into account the characteristics of the application of the absorbing material, of Composite Powder thickness of the absorbing properties were also studied. The results show that: with the media thickness increased from 2mm to 3mm, Composite Powder absorbing losses corresponding to the peak frequency gradually phase low-frequency mobile. The composite powder thickness 2mm, absorbing performance.

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