SGER: Distributed Measurements of Temperature, Moisture and Strain for Civil Engineering Applications in Subsurgace Using a Fiber Optic Sensor

这个SGER项目是为了开发一种新的光纤传感器组件，用于在扩展的地下环境（如道路堤防、墙壁回填和垃圾填埋场）中连续监测温度、湿度和应变。目前，光纤传感器的成本对于大规模应用于此类土木工程设施来说是非常昂贵的。该传感器基于受激布里渊散射（SBS）现象实现空间分布测量。它只需要一根光纤就可以测量不同位置的选定参数，满足地下监测的必要要求，是一种成本相对较低的工具。本课题的目标是构建一个原型SBS传感器系统，并在实验室中对其功能进行评估。该系统将由传感元件和信号发生器/分析仪组成。信号发生器使用一个单一的激光源，通过电光调制器进行调制，产生泵浦光波和探测光波。传感元件将使用标准光纤开发。两根裸露的纤维将用于测量应变和温度，并根据其信号变化进行校准。对于水分传感，第三根纤维将沿其长度间歇性地涂上水凝胶材料。采用半刚性、可渗透的复合聚合物纤维编织护套包裹水凝胶包覆光纤。护套将为纤维提供保护，并为水凝胶提供限制空间。水凝胶在光纤周围的受限空间中膨胀，预计会对封装的光纤产生轴向应变。轴向应变的大小将取决于膨胀的程度，反过来又取决于周围可用水分的程度。将进行试验台规模的实验室测试，以测试和验证SBS传感器的空间分布传感能力。应变传感实验将使用简单的滑轮和重量组件进行。湿度和温度传感将使用装有加热元件、热电偶、加湿器和湿度传感器的测试室进行测试，以控制和测量温度和湿度。在所有的实验中，传感器信号的变化将映射到实际测量值的变化。当温度、湿度和应变三个参数可能同时引起信号变化时，将测试和评估原型传感器的耦合效应。最后一组测试将通过将原型传感器嵌入一个实验规模的测试箱中进行，该测试箱中装满了不同含水量的土壤层，代表接近真实的地下环境。所提出的传感器组件及其方法旨在以相对较低的成本在更大的区域和深度上具有高精度的测量能力，从而显著推进地下民用基础设施系统监测的最新技术。该项目将涉及来自两个机构的具有不同专业知识的调查人员的合作。研究生将接触多学科和研究经验。

This SGER project is for the development of a new fiber optic sensor assembly for continuous monitoring of temperature, moisture and strain over extended subsurface environments, such as road embankments, wall back-fills, and landfills. At present, the cost of fiber optic sensors is prohibitively expensive for large-scale applications in such Civil Engineering facilities. The proposed sensor is based on Stimulated Brillouin Scattering (SBS) phenomenon to achieve spatially distributed measurements. It meets the necessary requirements of subsurface monitoring by measuring selected parameters at different locations with only a single fiber, rendering it a relatively low cost tool. The objectives of this project are to construct a prototype SBS sensor system, and evaluate its functions in the laboratory. The system will consist of a sensing element and a signal generator/analyzer. The signal generator uses a single laser source that is modulated through an electro-optical modulator to generate both pump- and probe- lightwaves. The sensing element will be developed using standard optical fibers. Two bare fibers will be used to measure strain and temperature as calibrated to their signal variation. For moisture sensing, a third fiber will be coated intermittently with a hydrogel material along its length. A semi-rigid and permeable composite polymeric fiber braid jacket will be used to encase the hydrogel-coated optical fiber. The jacket will provide protection to the fiber as well as a constrained space for the hydrogel. The swelling of the hydrogel in a constrained space around the optical fiber is expected to induce axial strain on the encapsulated fiber. The magnitude of the axial strain will be dependent upon the degree of swelling and, in turn, to the degree of available moisture in the surrounding. Bench-scale laboratory tests will be conducted to test and verify the spatially distributed sensing capability of the SBS sensors. The strain sensing experiments will be conducted by using simple pulley and weight assemblies. The moisture and temperature sensing will be tested using test chambers instrumented with heating elements, thermocouples, humidifiers and humidity sensors to control and measure the temperature and humidity. In all the experiments, the variation of the sensor signals will be mapped to the variation of the actual measurements. The prototype sensors will be tested and evaluated for coupling effects of temperature, moisture and strain when all three parameters may induce signal variation at the same time. The final set of tests will be conducted by embedding the prototype sensors into a bench-scale test box filled with layers of soil at different moisture contents, representing near real subsurface environments. The proposed sensor assembly and its methodology is envisioned to significantly advance the state-of-art in monitoring of civil infrastructure systems in the subsurface with highly precise measurement capability over extended area and depth at a relatively low cost. This project will involve the collaboration of investigators with diverse expertise from two institutions. The graduate students will be exposed to multi-discipline subjects and research experience.