<p>A fiber Bragg grating (FBG) pressure sensor using a composite structure comprising a square diaphragm, steel trusses, and vertical beams is proposed and studied. The deflection of the square diaphragm due to the applied pressure is transferred as an axial force on the FBG mounted at the end of the vertical beams. Measurement principle and stress analysis of the pressure sensor are introduced. The experimental results indicate that the pressure sensitivity of the sensor is 622.71 pm / MPa across the range of 0 to 2 MPa with a good linearity recorded at 99.996%, and the hysteresis and repeatability of the pressure sensor are calculated to be 0.6639% full-scale output (FSO) and 0.2773% FSO, respectively. In addition, the relative error of the sensor after temperature compensation was found to be 1.46%, which indicates an effective elimination of the effect of the temperature on pressure measurement.</p>
An ambient refractive index (RI) sensor based on a microfiber coil resonator (MCR) is proposed. Using the coupling wave theory, the resonant properties of the MCR are theoretically studied. And then, using the finite difference time-domain method, the sensing characteristic of the sensor is investigated and the dependence of sensing characteristic on the MCR parameters is examined as well. Results show that the sensor is extremely sensitive to the ambient RI variation. And, the microfiber diameter determines both the sensitivity and detection limit of the sensor. Further, the rod diameter determines the free spectral range of the MCR resonance spectrum and influences the detection range of the sensor. However, the sensor sensitivity is almost constant with the rod diameter change. So, for ensuring a good performance in actual experiment, the microfiber diameter should range from 400 nm to 1 μm, and the rod diameter should range from 20 μm to 2 mm. This work provides a guideline for future research on the RI sensor based on MCR.