Filber Bragg Grating Salinity Sensor

Salinity is an important physics parameter of solution. Marine environment and climate change is closely related with salinity variations. Real-time measuring salinity is of great importance to farming the sea, environmental protection, marine resource development and modern military. Nowadays, methods such as conductivity sensor and microwaves applied to salinity measurement all have their own disadvantages, which become more and more difficult to meet the rapid development of society. Therefore, it is particularly important to work to develop some new types of salinity sensors with good performance. In this paper, a new type of FBG sensor based on polyimide-coated for salinity measurement is proposed and fabricated. The detailed structure of the thesis is outlined as follow:(1)Some classic definitions, technologies of the salinity measurement and applications of fiber sensors are introduced. The development and inscription methods of fiber Bragg grating are briefly referred. A Fiber Bragg grating is written using phase mask method, while a 193nm excimer laser is used as photowriting source in the thesis; and then the growth of fiber Bragg grating is studied.(2)Longitudinal strain sensor model of fiber Bragg grating is established, which helps analyze sensing mechanisms of polyimide-coated FBG salinity sensor. Then the features, development and-applications are outlined in this thesis.(3)The fiber Bragg grating salinity sensor based on polyimide-coated is proposed and fabricated experimentally. When the temperature in the lab is 18℃and the coating layer thickness on the sensor head is 64μm, the sensitivity is 17.5pm/(mol/L). The relationship between sensitivity, response time and coating thickness is studied and analyzed in this paper; the research reveals that the sensitivity is linear with coating layer thickness and the coefficient is+0.2pm/(mol/L)μm. And the response time grows over the increase of coating layer thickness. The experimental results demonstrate that a propriety selection of coating thickness is needed in order to achieve suitable sensitivity and response time in specific application.