Study on Measuring System of Subsurface Contamination using Frequency Domain Reflectometry with Vector Network Analyzer by using micro waves.

地下污染问题是当今世界各国研究的一个重要课题。由于目前还没有成熟的、适用的传感器，地下污染物的定性评价往往面临困难，目前地下污染物的评价方法主要是通过取样（钻孔）的方法获取原状土样，然后在场外进行污染物的提取。这种方法将不利于获得一个很好的可能性，以获得一个准确的数据，污染率和浓度，这是非常重要的输入数据，在污染的地下溶质浓度的演变建模。应用所谓的FDR-V系统（具有矢量网络分析仪的频域反射法）来测量污染物的浓度。FDR-V方法是同轴探针法（单端口反射法和S参数），可以测量1~18GHz的复介电常数。为了测量污染物的浓度，FDR-V系统分离两个反射，其由频域中的复介电常数的真实的部分和虚部分组成。实验中以油为污染物，分析了油和水的介电常数不同对光谱的影响。因此，本实验表明，在饱和和非饱和条件下测量污染物浓度是可能的。

Nowadays, the subsurface contaminant problem is a very important subject in all over the world. The study on this subject may often face with the difficulty in evaluating qualitatively the constituents of contaminated subsurface, like soil, pore air and pore water, because there is not yet a well-established and applicable sensor for such purpose.For evaluating subsurface contamination at present time, the undisturbed sample is commonly taken out by sampling (boring) method, and then the contamination is extracted offsite. This method will not favor a good possible to obtain an accurate data on the contamination rate and concentration, which are very important input data for modeling the evolution of solute concentration in the contaminated subsurface.Accordingly, as the purpose of this study is to develop the measuring system for subsurface contamination, what so-called FDR-V system (Frequency Domain Reflectometry with Vector network analyzer) was applied to measure the concentration of contaminant. The FDR-V method used in this study is the coaxial probe method (one port reflective method and S parameter) which allows the measurement of the complex dielectric constant from 1GHz to 18GHz. For the purpose of measuring the concentration of a contaminant, the FDR-V system separates two reflectives, which consist of a real part and an imaginary part of complex dielectric constant in the frequency domain. In this experiment, oil was used as a contaminant ; and then the spectrum difference were analyzed based on different dielectric constant of oil and water. Thus, this experiment indicates that it is possible to measure the concentration of contaminant both in saturated and unsaturated condition.