Researching for electromagnetic wave-absorbing characteristics

• Main Authors: Jun Wan, 萬軍
• Other Authors: C. C. HWANG
• Format: Others
• Language: zh-TW
• Published: 2004
• Online Access: http://ndltd.ncl.edu.tw/handle/80360107021875523936

碩士 === 國防大學中正理工學院 === 應用化學研究所 === 92 === ABSTRACT NiZn ferrite with the chemical formula (Ni0.5-xZn0.5-xM2xFe2O4, M=Co, Cu, or Mg, and x=0 or 0.05) were synthesized by a combustion synthesis method by using metallic nitrates and urea ((NH2)2CO) as reactants. The nanocrystallite of these materials were mixed with a thermal-plastic polyurethane (TPU) elastomer to be a microwave-absorbing composite. The complex relative permittivity and permeability of the absorber were measured in the frequency range of 2-12 GHz. The eflection loss (R.L.), matching frequency (fm) and matching thickness(dm) were calculated using the theory of the absorbing wall. Effects of both the particle size of ferrite and the dopant presented in the ferrite on the electromagnetic properties and microwave-absorbing characteristics were investigated. It was found that nanoparticles around 40 nm exhibit higher reflection loss than those of micro-sized powders and than those with size less than 25 nm. Also, it was shown that the Co-, Cu- and Cu-doped NiZn ferrite-TPU composites could be designed to be more negative than -20 dB in the frequency range of 2-12 GHz to become promising materials for microwave absorbing application. These doped ferrite-containing composites have more effective microwave-absorbing characteristics than undoped one.