Simultaneous measurement of temperature and pressure sensor for oceanography using Bragg gratings

Abstract

Pressure and temperature are fundamental properties of the oceanic water. They have varying effects on the processes that take place in oceans be they biological, physical or chemical while pressure always increases with respect to surface when you go down, temperature has a more complex variation with respect to the depth. Various tools and techniques are available to measure these properties. A combination sensor with high accuracy and response time would enable better measurements of these two parameters. This paper presents a novel structure based on simultaneous measurement of temperature and pressure sensing using Fiber Bragg grating (FBG) sensors. For this, proposed sensor heads for both temperature and pressure. Temperature measurement, two different types of sensor heads has been designed for this implementation. The first sensor head consists of a FBG which is fixed between ceramic block on one side and a bimetallic strip made up of aluminum and copper on the other. The second sensor head consists of the FBG which is fixed between two bimetallic strips. For pressure, in first type the FBG is fixed between silicon rubber foil and sensor head wall. In second method the FBG is fixed between two silicone rubber foils. The pressure on walls of silicon rubber foils elongates FBG, which results in shift of wavelength. Theoretical studies carried out on these proposed sensor heads resulted in an increase in temperature sensitivity of about six times greater than that of bare FBG sensor and pressure sensitivity of about eight times greater than that of bare FBG. Further, the proposed sensors have shown good linearity and stability.