Study On A Measurement Method Of Liquid Permittivity Based On Rectangular Waveguide

The microwave-chemistry reactor is a core part of the microwave chemistry experiment system. Most of the liquid chemistry reaction could be put into a tube or a beaker inside the microwave chemistry experiment system. In a microwave chemistry experiment, to obtain the real-time complex permittivity is of great importance to understand the reaction process.There are several methods to achieve the complex permittivity of liquid in a rectangular waveguide such as the short-end waveguide method, the resonant cavity perturbation method, the waveguide perturbation method, and so on. Each method owns some advantages in measuring the complex permittivity, but it is not convenient to achieve the real-time complex permittivity of the liquid during chemistry reaction process. While using the waveguide perturbation method to achieve the real-time complex permittivity, we have to get the sample from the experiment system continually. Both the short-end waveguide method and the waveguide perturbation method are suitable for the measurement of the complex permittivity of solid. In this thesis, another method is used to reconstruct the complex permittivity of liquid in the waveguide from the measured S parameters.The electromagnetic field distribution of a waveguide with a liquid filled test tube (two dimensions) is discussed theoretically, and the S parameters are obtained. Then, the field distribution and the S parameters are simulated in three dimensions basing on the finite element method.A numerical simulation base on the finite element method is used to get the principle that S parameters varies with incident wave frequency, the permittivity of liquid, and the height of the liquid. The impact of the test tube on scattering...