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

目前，地下污染问题在世界范围内都是一个非常重要的课题。由于目前还没有一种完善的、适用的传感器，对污染的地下成分，如土壤、孔隙空气和孔隙水进行定性评价往往是这一课题的研究面临的困难。目前评价地下污染时，一般采用取样（钻孔）法取出未受干扰的样品，然后在现场提取污染。这种方法不利于获得准确的污染速率和污染浓度数据，而污染速率和污染浓度是模拟污染地下溶质浓度演变的重要输入数据。因此，由于本研究的目的是开发地下污染的测量系统，因此采用FDR-V系统（Frequency Domain Reflectometry with Vector network analyzer）来测量污染物的浓度。本研究中使用的FDR-V方法是同轴探头法（单端口反射法和S参数），可以测量1GHz到18GHz的复介电常数。为了测量污染物的浓度，FDR-V系统在频域上分离了由复介电常数实部和虚部组成的两个反射体。在这个实验中，油被用作污染物；然后分析了不同介电常数下油和水的光谱差异。因此，本实验表明，在饱和和不饱和条件下都可以测量污染物的浓度。

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.