Graphene diaphragm integrated FBG sensors for simultaneous measurement of water level and temperature

A graphene diaphragm integrated silica fiber Bragg grating (FBG) based sensor head was developed for simultaneous determination of water level and temperature. This new design used two FBG sensors with uniform grating made of SMF-28 fiber with 1550 nm of central wavelength, bandwidth of 0.5 nm, 4 mm length and 90% reflectivity. The response of the sensor to water level was monitored in terms of Bragg wavelength shift, which is proportional to the strain. Upon immersing inside the water column, the diaphragm gets deformed due to a strain originated from the water level imposed hydrostatic pressure. A linear response of the sensor head was achieved for water level in the range of 0-100 cm. The FBG based sensor head revealed high detection sensitivity ∼24.84 pm/cm. The temperature measurement sensitivity of the sensor was 13.31 pm/°C in the range of 27-77 °C. The water level detection sensitivity was found to reduce with increasing thickness of the graphene diaphragm.