Research On The Microwave Absorption Properties Of Dielectric And Magnetic Power And Its Composite With Paraffin

With the development of modern society, the electronmagnetic (EM) wave devices have been widely used. But the increasing usage of them have been drawn more attention on electromagnetic interference (EMI) and electromagnetic compatibility (EMC) problems as a special kind of environmental pollution. Therefore, it have caused people more and more concerns for the development of new microwave absorbing materials. New microwave absorbing materials are different from the old ones. They require the material to meet the requrements-thin, light weight, wide bandwidth and strong absorption properties, which means that the materials should be "thin, light, wide, strong absorption". At the same time, the materials also need to adapt to various environments and have the corrosion resistance, high temperature resistance, impact resistance, anti-nuclear radiation characteristics. The study of dielectric material becomes a research hotspot due to its low density and corrosion resistance.This dissertation mainly discussed the microwave absorption properties of conducting polymer-polyaniline (PANI), graphite and graphene/paraffine composites and polyaniline/magnetic powder/paraffine composites. The permittivity of the composites can be adjusted by changing the preparation method and the weight fraction of polyaniline, graphite and graphene. The study and results are as follows:(1) The polyaniline were synthesized by using aniline as the raw material, hydrochloric acid as dopant and ammonium persulfate as oxidant. And then, we studied the properties of the polyaniline under pH=1-4. As the results stated, the permittivity of composites can be increased with the increase of the content of polyaniline. For50wt.%PANI/paraffinee composite, the peak position, the intensity of the peak of the reflection loss and bandwidth were explained by using the interface reflection model or the quarter-wavelength (1/4) matching model. Determining the reflection loss peaks positions refers to the peak frequency of calculated reflection loss resulted from the test of permeability and permittivity falls on the the calculated results of peak position curves obtained from interface reflection model. The energy reflected from the interface and the energy of the eclectromagnetic loss at the peak frequency of reflection loss were calculated by the S parameters. And the change of intensity of reflection loss can be explained by the interface reflection model. Meanwhile, the bandwidth formula of reflection loss peak were obtained by using the interface reflection model, which explained the change of the bandwidth. The density of common metal magnetic materials are about8g/cmJ, and most of ferrite magnetic material are more than5g/cm3, while the density of polyaniline is about1.3g/cm3. Thus, as a kind of absorbing material, polyaniline would be lighter than the magnetic material when the thickness is the same.(2) When the polyaniline added to the CO2Z powder/paraffin composite and their content change from0wt.%to50wt.%, the samples would become thinner as the same frequency of absorption peak. And the35vol.%Co2Z/30wt.%PANI/paraffin composite has good results at2,5and7mm. It has two perfect match points and their bandwidth are up to5and11GHz when designated value is-6dB. Besides, the values of absorption peaks are less than-10dB at the range of6.0-1.5mm and2.5GHz-18GHz. When the polyaniline added to the carbonyl iron powder/paraffin composite, the frequency of absorption peaks moved significantly to the low-frequency direction at6mm under same paraffin-weight ratio. Their frequency of absorption peaks are in line with the quarter-wavelength (λ/4) matching model.(3) Different types of powder/paraffin composites also have perfect match points. For30wt.%graphite powder/paraffin composite, the values of absorption peaks are less than-10dB at the range of6.0-1.1mm and2.8GHz-18GHz. For50wt.%of graphene powder/paraffin composite, the values of absorption peaks are less than-10dB at the range of3.7-1.8mm and3.1GHz-7.3The absorption peaks at2GHz and10GHz are given, and it found that they have a certain peak intensity and bandwidth. Since the density of common metal magnetic materials are about8g/cm3, and most of the ferrite magnetic material are more than5g/cm3, while the density of graphite and graphene are less than3g/cm3, so as a kind of absorbing material, graphite and graphene would be lighter than the magnetic material when the thickness is the same.