Correlation Of Structure And Dielectric Properties Of Composite Material

The electromagnetic radiations are becoming more and more seriously with the increasing number of electronic devices in our daily life. Now there is a widespread concern on the countermeasures and defense of electromagnetic pollution, in which the electromagnetic wave absorbing materials appealed lots of interests. Further more, dielectric absorbing materials is a kind of key fields of these, and the accurate methods for measuring and controlling of the complex dielectric constant of the materials which are playing the crucial roles in preparing and producing process. What’s more, those methods are also the key factors for the whole designing and research in electromagnetic functional materials especially, in multiphase composite materials.Recently, the measurements for dielectric constant mainly include network parameter analytics, waveguide method and resonance method. Each of them contains several sub methods and possesses various advantages and features which demand strict shapes or sizes. Because of the structures of the materials, these requirements are difficult to be met, in other words, the samples can not be processed to highly precious small shapes. Although there is free-space method for measuring complex permittivity, the intrinsic problems such as multiple-value and phase-shift ambiguity limit this method. To the best knowledge, there is not a perfect method for testing big size, porous materials, or liquid materials yet; all the researches are still in the exploration stage.In this thesis, the relationship with dielectric constant and basic equality in static electric field was discussed in theoretically. Reflection of plan wave was the main research method, and transmission line theory formula was derived from essential electromagnetic wave equation. After that, expanded calculation was performed to gain absorption contours and conditional selected curves, and the conditions which were homologous with non-reflective curves were used to select the curves. Then these curves were took advantage to explore a new way to invert the equivalent complex dielectric constant.There were lots of experiments were finished to prove the above-mentioned theories. The curves of complex dielectric constants of various coaxial tube samples were tested and the same to the absorption curves of big size samples. The values and positions of peaks in absorption curves were used to draw absorption contours which can be compared with conditional selected curves to gain the complex dielectric constants of samples. After that, theoretical designing sufficient were preformed to the experiments.Theoretic simulation of several spots selected from the non-reflective curves was researched. Meanwhile, absorption curves of different samples with various thicknesses were inverted and simulated to compare the experimental result, which showed perfect match. In this research, we offered a new effective way for testing complex dielectric constant of big size, porous materials, and liquid materials from the view of macroscopic. This method avoids disadvantages of small samples which just present parts of the whole features and makes it truthful in daily services. Besides, our research provides a theory to design new electromagnetic wave absorbing materials and there is significance for designing or research in large structural electromagnetic functional materials.