Polymer Based Miniature Fabry-Perot Pressure Sensors with Temperature Compensation: Modeling, Fabrication, and Experimental studies
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Miniature Fabry-Perot (FP) pressure sensors have been of great interest because of their advantages of small sizes, high performance, and immunity to electromagnetic interference. Most of these sensors are built with silicon/silica materials that have good mechanical, chemical, and thermal stabilities. However, due to the large Young's modulus of silica/silicon, developing a high sensitivity miniature sensor becomes difficult. In addition, fabrication of these sensors often involves high temperature fusion bonding and harsh acid etching. On the other hand, a polymer material becomes an attractive choice for high sensitive and miniature pressure sensors due to its small Young's modulus relative to that of silicon/glass. Moreover, polymer processes can be performed under ambient pressure and temperature without hazardous chemicals. However, a polymer-based sensor suffers from high temperature sensitivity, which must be compensated to obtain accurate pressure measurements. In this dissertation, three types of polymer based FP miniature sensors for static or quasi-static pressure measurements are investigated through modeling, microfabrication, and experiments. First, co-axial and cross-axial FP sensors with a built-in fiber Bragg grating (FBG) for temperature measurement and compensation are studied. In both sensors, the FP cavity is precisely self-aligned with the optical axis by using the fiber as a natural mask, which eliminates the need for a photo mask and tedious optical alignments. Second, a FP sensor composed of a UV-molded optical cavity with a pre-written FBG is developed. For the first time, a UV molding process with an optical fiber based mold is developed for fabrication of miniature FP sensors. This process enables high accuracy optical alignment for UV molding. Taking advantage of the UV molding process, the third type of sensor features a hybrid dual FP cavity for simultaneous temperature and pressure measurements. A novel signal processing method is developed to retrieve the multiple cavity lengths with an improved speed, resolution, and noise resistance. Experimental studies show that these polymer based sensors have good pressure and temperature sensing performance as well as temperature compensation capabilities. In addition, blood pressure and intradiscal pressure measurements of a swine are performed, which demonstrates the feasibility of these sensors for biomedical applications.