Development and Application of Disposable Birefringence Material in Fluidic Liquid Concentration Sensor

• Main Authors: Li, Kai-Hsuan, 李凱軒
• Other Authors: Twu, Ruey-Ching
• Format: Others
• Language: zh-TW
• Published: 2018
• Online Access: http://ndltd.ncl.edu.tw/handle/p6679b

碩士 === 南臺科技大學 === 光電工程系 === 106 === This dissertation focuses on the application and development of optical birefringent plates in angle, micro-displacement, and liquid refractive index sensors. The impacts of the birefringent materials in harsh environments (temperature changes, corrosive liquids) are studied. Finally, non-contact, disposable birefringent sensors were successfully applied in the fluid monitoring systems. On the measurement system, a commercial electro-optic modulator was used for phase modulation in a common-path heterodyne interferometer. The phase information is measured by a lock-in amplifier, and the physical quantity under test is obtained through the measured phase changes. When an orthogonally polarized light enters the birefringent plates obliquely, an optical path difference between two orthogonal polarizations occurs due to the difference in refractive index of the material. At the same time, a phase delay is generated in the two orthogonal polarizations. According to the related formulas and mathematical simulations, three different birefringent materials such as KTP, BBO, and PET were explored systematically to evaluate the dependence of the phase change and sensitivity on both the incident angle and the refractive index of environmental medium. Based on these characteristics, the design and fabrication of the compact displacement sensor (CDS) is achievable. When the fluid passes through a transparent container, the displacement of the probe beam is dependent on the refractive index change of liquids due to the change of the injected fluid concentrations. The CDS can be used to detect the displacement caused by the change of fluid concentrations. The measured phase can be used to decide the fluid concentrations by the relations between the displacement and liquid concentration in the CDS. Moreover, the use of inexpensive PET attached on the triangular container has been validated preliminary as a disposable sensing unit. In addition to comparing the effects of different thicknesses of PET, the measurement stability was also studied for different attached methods. In order to increase the sensitivity of measurement, it is also proposed to adopt a prism coupling to overcome the limitation of the incident angle due to the total reflection effect. Therefore, the sensitivity and resolution of the refractive index measurement are also greatly improved under the increase of the incident angle. We have successfully developed a disposable fluid sensor. As a word, we also discuss the applications of various structures under different concentration resolutions.